Energy Efficiency Waits For No Man!

Expecting the unexpected

2010-10-15T14:19:00.000-07:00

Well, faithful readers, there is no easy way to put this, so here it is: the time has come for Energy Efficiency Man to depart from Efficiency Manor, his home for the last 14 years. In life one must always expect the unexpected, and in this case, the unexpected has arrived in the form of major life changes.

I will do my best to perform the final yearly analysis on the house, given that the major cooling season is now over, and the remaining few months' electric usage can be estimated pretty well from the previous year.

My overall experience with the house that awakened my interest in Energy Efficiency (lo these 5 years ago) was a positive one. From the start, the house was surprisingly well air-sealed (too well, perhaps, for maximum air quality without a fresh-air ventilation system), but left a lot of low hanging fruit in terms of attic improvements (attic venting, radiant barrier, and insulation). I also learned the pros and cons of the various lighting options (LED, CFL) and paid for some fine improvements in the duct sealing as well. The upshot of all those improvements was a far more comfortable house that saved a lot of money (over 50%) each month.

One regret is that the south-facing section of roof, which due to lack of shading would work quite well for solar panels, is left unadorned with my departure. It is possible that I had completed enough efficiency work for the installation of either a solar water heater or a solar PV system to make sense as the next step in the low-hanging fruit gathering. Longtime readers will already know that a kilowatt-hour saved is the same as a kilowatt-hour generated; they are two sides of the same coin. The least expensive way forward for me was to stop wasting so much energy, but once that was done, solar energy could have made sense. Perhaps the next owners will see it that way.

Another regret is that the windows, while double-paned, are nowhere near as good as modern high-end windows, but replacing double-paned windows is rarely worth it moneywise, as research seemed to consistently suggest.

One thing that I do NOT regret, but will also NOT miss, is the large number of hours spent in the attic, measuring and stapling radiant barrier, digging through insulation trying to remove soffit-blocking batts, or just looking around, planning and scheming. This type of work, while not exactly fun, was incredibly rewarding once the results of the efforts were clear.

This will not be the end of the blog; EEMan has to live somewhere, and that somewhere will use energy, and likely could use his attention. More on that in future posts.

Fun with the Passivhaus

2010-09-16T20:54:00.000-07:00

If you haven't already looked, I recommend you go take a gander at the summary of the Passivhaus performance specifications. It is worth noting that the summary is just that; the Passivhaus approach is far more nuanced and detailed, and seems to be an integrated, carefully balanced energy-flow approach to design. Nonetheless, it does contain some performance requirements, and it might be fun to compare my slightly-improved-from-awful house with a state-of-the-art set of requirements.

For the fun of it, let's compare my energy usage for heating and cooling to the Passivhaus standards. To meet Passivhaus:

Heating must be less than 15 kWh/square meter per year. Mine is roughly 52.
Cooling must be less than 15 kWh/square meter per year. Mine is roughly 24.
Overall energy must be less than 120 kWh/square meter per year. Mine is about 86 (this includes all energy, not just heating and cooling).

So interestingly, for overall use, my house seems to meet the Passivhaus standard. This seems like an amazing result, since real Passivhaus houses have:

16-inch thick insulated walls
incredibly airtight building envelopes
multipane low-e gas-filled windows
specially designed air exchange systems
carefully planned and balanced heat flows

...none of which I have. But if one looks at the results more closely, one can see that, not shockingly, I won't make Passivhaus certification anytime soon. I'm over budget on the heating use by nearly a factor of 4, and I'm over budget on the cooling by a factor of 1.5 or so. The heating result is particularly poor by comparison since the Central Texas climate is a _whole_ lot warmer than that climate in northern Europe, where the standards were developed. So if my house is spending 4 times more energy per unit of area than a passivhaus, and doing so in a far milder winter, one need not be very impressed with my home's wintertime performance. In fact, if you compare in a way that cancels out the difference in climate by measuring kWh per Heating Degree Day, my house turns out to be more than 6 times worse than the passivhaus per unit of heating per unit of area. That, by the way, is _after_ my attic improvements which increased my wintertime efficiency by 30%. Ouch.

In fact, it seems pretty likely that the overall mildness of the climate here is the main reason that my house falls below the 120 kWh/square meter per year overall energy limit. If there's not all that much heating to be done, and not all that much cooling to be done, it's pretty easy to not spend that much energy even if your house is not all that efficient. That being said, I'm still happy to be under that number (unless my math is wrong... I can post the spreadsheet by popular request).

Another (truly fascinating!) result that I discovered doing this analysis is that I expend far more energy heating during the 3-4 months of relatively mild wintertime than I spend cooling in the 4-5 months of hot, sunny summertime. In fact, despite our long and brutal summers, I spend more than twice as much energy heating the house with the natural gas forced-air heater than I do cooling the house with the air conditioner.

I speculate that this additional expenditure of energy may be due to two factors:

A large portion of summertime heat gain is through solar radiation hitting the roof, and the radiant barrier now rejects nearly all of that heat, greatly reducing my cooling load. By contrast, winter heat loss is more evenly spread through windows, walls, and ceiling. In my case, I have not improved either the walls or windows, so their relative inefficiency is costing me more in the wintertime.
In the wintertime, my heater has to more than fully replace the heat that has left the house. Every 1 kWh of heat energy that leaves the house has to be replaced by slightly more than 1 kWh of energy of burned natural gas (due to imperfect efficiency in the burner system). However, in the summertime, I only have to move heat out of the house, which is far more efficient; my 14 SEER air conditioner can move (ideally) 3.7 kWh of heat out of the house by "burning" only 1 kWh of electricity. (See description of COP and SEER here to understand why).

Indeed, the careful reader may observe that if reason #2 is entirely accurate, then I should be expending almost 4 times as much energy in the winter as the summer... and yet, I am only expending just over twice as much. I think that the difference is due to the fact that the internal home heat load (my body heat, the heat generated by lights, televisions, stoves, refrigerators, blogging computers, etc.) works against me in the summer, but works for me in the winter.

In fact, this brings us back to the coolest (warmest?) feature of the Passivhaus: the internal heat load IS their central heat. These houses are so efficient that, even in frosty places like northern Europe, the internal heat of the occupants and their activities is generally enough to keep the house warm. So in effect, the elimination of central heat (and all the ductwork, grilles, filters, etc. associated therewith) helps to pay for all that added insulation and those nice windows, not to mention the fresh air heat exchanger. Brilliant! The houses still tend to cost more (I've seen numbers from 10% more than "standard" construction, down to as little as 3% more as practices and equipment are standardized). However, such price differences can get paid for pretty quickly, particularly in extreme climates.

Given the particulars of Central Texas, I doubt we will be without air conditioning in our houses anytime soon, especially since even if _all_ external heat were rejected, we'd have to deal with moving internal heat load outside. However, it's within the realm of possibility that central air conditioning might become less common; I have seen new small efficient houses with no central A/C and no ductwork. These are operated with a single wall unit A/C at a roughly central location, typically near the kitchen, and simple air holes placed over interior doors to allow airflow throughout the home. Combined with a high-efficiency heat-exhausting fan at a convenient point in the ceiling (such as a bathroom where you want moisture reduction anyway), these systems apparently work quite well. A small step towards a Passivhaus-type concept, but one in the right direction, and a very affordable one as well.

Moderate efficiency, radical conservation!

2010-09-15T20:44:00.000-07:00

As I wait for the end of September, what I think of as the official end of the air conditioning season here in Texas (although there is little doubt the A/C will run a bit in October as well), I have musings about the way of thinking about energy efficiency.
First, to me, the definition of "efficiency" is the accomplishing of a given task fully and completely but with less use of energy than the way the task was accomplished previously. For example, if the task is to move 2 people from point A to point B, using a smaller vehicle than before to carry said people will typically result in the task being performed more efficiently, in that the task is completely performed, but less fuel was burned to accomplish it.
There is a similar concept called "conservation", which does not stipulate necessarily that the exact same task be performed, but simply that energy not be used unnecessarily. For example, to look at our example from a conservation mindset, one might ask some questions before one decides how to move the people from point A to point B:

How far is it from point A to point B, and what mode of transport is appropriate for this distance?
What is the goal of moving 2 people from A to B? Is there another way to accomplish this goal that does not involve moving people at all?

Depending on the answers to these questions, the conservation mindset might produce solutions to the problem ranging from "send them via bicycles" to "let them make a phone call from point A, and stay there". In effect, the conservation mindset allows one to question the very reason energy is being used in the first place, and to think differently about how certain needs are met.

In this blog, I have focused much more on the "efficiency" mindset, in that it is the least amount of change from the way things are done today. There should be no great mental hurdle for people to understand that doing the same thing in almost the same way, but using less energy while doing it, is a great thing. Thus, living in a house with air conditioning and heating is not questioned, but the amount of energy those systems use and how they use it is questioned, analyzed, and improved.

However, the conservation mindset allows the possibility of even greater improvements. For example, consider air conditioning from the conservation point of view. This point of view asks the question: "What is the point of conditioning the roughly 20,000 cubic feet of air in my house, day in and day out, for about 5 months every year? What am I trying to accomplish? Is there a less energy-intensive way to accomplish this goal?"
As it turns out, the main point of conditioning 20,000 cubic feet of air every day is to make my roughly 2.5 cubic feet of body more comfortable. Is it possible that there is a way to make that body more comfortable without using all that energy? Certainly, in the winter when the picture is reversed, and I want to warm that 2.5 cubic feet of body, I can put warm clothes over the 2.5 cubic feet part of the problem, and save a lot of energy! As an aside, that works well in the winter, because of course, our bodies are quite active producers of heat, so slowing the flow of that heat from the body produces excellent results.
Writing the above, I am reminded of the fine progress the German people have made on energy efficient houses in the cold. In fact, it looks like we are beginning to adopt some of those strategies here. I particularly enjoy the fact that these houses are so efficient as to recognize that you can even capture the heat from the air that naturally escapes the house by planning to have it escape through a heat exchanger, so that the heat is transferred from the outgoing stale air to the incoming fresh air, saving energy even as the house is ventilated with what would have been cold outside air. That strikes me as the product of a conservation mindset, although a lot of the rest of the Passivhaus construction (super thick insulation, multipane windows, etc.) probably falls more under the rubric of extreme energy efficiency, a sort of "if R-20 insulation is good, R-60 insulation is better" approach.

At any rate, it seems to this humble blogger that the combination of the tame but disciplined approach of energy efficiency, along with the potentially more radical questioning approach of conservation yields the most powerful punch against our nefarious enemy, out-of-control energy use. Food for thought along those lines: if I have tripled the cooling efficiency of my house (and I have) using only "mild" efficiency techniques, what could be accomplished with a full conservation mindset? Out-of-the-box suggestions and discussions welcome!

Looking forward to end-of-summer numbers soon, and perhaps analysis updates to follow. Until then, be efficient and conservation minded!

What is that radiant barrier thing?

2010-08-30T22:11:00.000-07:00

The radiant barrier seems to be hardest attic improvement for the inexperienced efficiency seeker to understand. Most of us have an intuitive grasp of the other major improvements: additional insulation should work, if we have no other understanding of the physics, just on the basic principle that "if some is good, more is better." Additional ventilation should work just because we understand that breeze cools our bodies, and therefore it can cool our houses. Never mind that the principle is different; our houses don't sweat and use evaporation to cool (OK, some with swamp coolers do), but instead use ventilation to replace super-hot air with just hot air to reduce the temperature difference between the attic space and the conditioned space.

But with the radiant barrier, very few of us understand how something reflective could possibly work from inside the attic. Sure, we understand that if we put silvery reflective stuff on the roof or at the very least painted the roof white we would reflect a good bit of the sun's energy back out into space, and these things are quite true. But, as it turns out, installing reflective barrier properly inside the attic itself works and works dramatically well, as my own experience demonstrated. It turns out that the effect of covering the inside of a non-shaded attic with radiant barrier foil is about the same as covering the entire thing with shade from a shade tree. In effect, the sunlight's energy gets reflected back out. While this is different from tree leaves in that the tree absorbs the energy to make chemicals it needs, rather than reflecting the energy back, the upshot is the same: the energy does not get into your attic. It also turns out that this is only the case if the foil barrier is installed with an air gap of at least an inch (or so) facing a reflective side of the barrier, and whether that reflective side faces up or down is irrelevant. The barrier is ineffective if it is positioned between two other surfaces with no gaps. Hard to grasp intuitively? Yes. But impossible to deny in experiment after experiment.

Because of lack of intuitive understanding, a lot of folks lean towards additional insulation as the first improvement to make. But in hot climates such as ours in central Texas, the radiant barrier can be a good bit more effective, depending on the initial state of the house.

I have said it before, but it bears repeating: there are 3 physical ways that heat enters your home in the summer: radiation, convection, and conduction, and there is a solution for each of them. The absolute best way to keep that heat out of your house is probably to spend a little time and money on each of the 3 ways, rather than going all-in on a single solution. Thus, a radiant barrier to handle the radiation of heat, ventilation to utilize convection in your favor, and a little additional insulation to fight conduction might well do wonders for you. This approach actually tripled the efficiency of my own house; of course, your mileage may vary. Your house may be a lot less of a solar oven than mine was at the beginning.

So don't be afraid of that barrier, folks! It is affordable, it has no moving parts to break down, and it works!

The Key Principle of Energy Efficiency

2010-08-18T15:24:00.000-07:00

I have talked to many people about energy efficiency. Almost invariably the discussion turns towards residential solar panels and high performance windows. Now, while these things are important, solar panels are _not_ an efficiency measure but instead an electrical generation system. High performance windows, while they are an efficiency measure, are probably the least cost-effective efficiency measure that one can undertake according to the vast majority of research I've read along with my own personal experience.
To folks at this level of knowledge, I would point out one major tenet of energy efficiency as I see it:

For a grid-connected house, saving energy is the same thing as generating it.

From the point of view of the electrical grid, a house that uses 1 kWh less per day looks exactly the same as a house with a solar panel system that generated 1 kWh that day. Both houses take 1 kWh less from the grid than their unimproved counterparts on any given day, and therefore both houses are reducing their energy bill by the same cost per day, and reducing the environmental impact of generating their required energy by the same amount.
In short, and it is worth repeating, those solar panels or wind turbines on the house are performing the exact same function as any energy efficiency improvements. Because of that fact, if you want to determine whether to improve efficiency or add generation to your home, it is logical to compare:

The up-front cost and effective interest rate of the improvement
The environmental impact of the improvement
The impact on the home's value of the improvement

These should be the major factors to consider when deciding whether to go with a generation option (typically solar these days) or efficiency. Bottom line: don't just assume you have to go with electrical generation to reduce your home's ecological footprint. The same amount of money will likely offset more energy usage if spent on efficiency than if spent on generation, depending on the starting efficiency of your home. If your house is anything like mine was when I started this whole adventure, you have a lot of low-hanging fruit to gather, for surprisingly little money and high rate of return, before it makes sense to consider generation.
That being said, the prices of solar panels have been dramatically reduced and ongoing efforts are being made to reduce installation costs. With appropriate subsidies a solar generation system may make good sense, at least for the homeowner. Whether it is worthwhile in the larger community, when considering the other things that the subsidy money might have been spent on in our current era of budget shortfalls, is perhaps a tougher question to answer.

So is Energy Efficiency Man bashing solar panels? Not in the least. The more the better, particularly in the Texas summer. Here in Austin, we had an all-time record electrical usage number a couple days ago. Solar panels will and do undoubtedly help reduce our peak summertime loads. However, EEMan would like to see every one of those solar panel-covered houses looked at for low-hanging efficiency fruit, so that we can get the maximum reduction in load on the grid. A net-zero (or energy positive) house is a great thing to aim for.

Until next time, be safe and be cool!

Reflections midway through the summer

2010-08-09T19:28:00.000-07:00

We are now a good half of the way through the summer of 2010. Here in Central Texas, we've had a relatively cool June and July, with some clouds and even some rain, but August is already looking pretty rough. Our traditional summer high-pressure system has finally blanketed the state, capping any storms before they can form, and keeping high temperatures around 100 F.
It is too soon for another analysis of summertime energy performance (although my July usage was pretty darned good), but I am looking forward to the end of September when I'll have another good round of data in place for comparison. Since I haven't made any efficiency changes to the house since last summer, it might be nice to see if the "effectiveness" numbers that I've used to measure how well the house performs independently of the weather match up from last year to this year. If there's not a lot of change from the 2009 to the 2010 number, we can probably assume that "cooling effectiveness" is indeed a useful measure.
In the meantime, I am trying to think what I might do with this blog. My intention in starting it was to share some of my experiences so that other house-dwellers might learn how to, and perhaps be inspired to improve their own homes. Also, I wanted to get across a few major themes, including:

Very low materials-cost improvements can provide significant savings
Attacking heat on multiple fronts yields major synergy
Return On Investment for efficiency can be better than most traditional investments

I think that I have done that, and hopefully amused and entertained a few people along the way.
But this begs the question: what now? I think I've grabbed the lowest-hanging efficiency fruit already. Although more can always be done, I find it unlikely that I'll improve the house further in the near term, due to the larger cost increments that will now be involved. So what will I write about?
I suppose I'll have to start writing about whatever ends up on my mind. There is much going on in the larger world of energy efficiency, energy future, grid planning, and all manner of related topics outside the microcosm of my now less-energy-inefficient house. I may need to add my voice to the many already talking about these larger topics. If nothing else, I now know from personal experience that there is much that can easily be done in this area.
In the meantime, if you, the intrepid reader, want to examine the journey that got me to this point, I encourage you to start from the beginning (which includes an Executive Summary with links to the various posts) and learn what you can about the lore of improving that enemy of efficiency, the single-family dwelling. Until then, adieu!

A Long Awaited Analysis

2010-03-15T19:56:00.000-07:00

I hope that everyone out there is enjoying the beginnings of spring. Along with the ice thawing, the snow melting (yes, even central Texas had snow this year), and the birds singing, it is time now to turn to that even more important harbinger of spring: the February natural gas bill.
Like the swallows returning to San Juan Capistrano, the arrival of this document signals the "beginning of the end" of the heating season, if not the absolute last heating day of the year, and it hopefully foretells a spring that might last several weeks before the air conditioner must reluctantly be fired up. Its arrival also signals the renewal of that great art form both revered and reviled by nearly all sentient beings, data analysis.
It is with these words that we first take a quick look at the seasonal variability of the last 4 winters so that we can get a feel for the raw and weather-adjusted numbers. For our purposes I am defining a winter as the 4 months of November, December, January, and February, since these are the months that, in my area, cause me to have my highest natural gas usage. For reference, my home is heated by burning natural gas and blowing the heated air throughout the living area via the ductwork in the ceiling.
We will measure the seasonal variability of winter in a complementary way with the method we used for summer: instead of "cooling degree days" (CDDs) we will use "heating degree days" (HDDs). The weather data I am using is in HDD's base 65 Fahrenheit, which means that a day with an average temperature of 64 degrees Fahrenheit would add 1 HDD to the total HDDs for the month; 5 days of 62 degrees would add (5*(65-62)) = 15 HDDs to the total for the month, etc.
So, by this measure, more HDDs would mean a cooler day, week, month, or season, depending on what timeframe we are looking at. First, let's look at the data for the winter season for each of the last 4 years:

I have put the most recent winter on the left on the graph with years getting older as you look right. As you can see, this winter was roughly 30% colder than last, and probably at least 20% worse than the average in terms of Heating Degree Days. Although I don't have data on this, it certainly seemed like there were more cloudy and/or rainy days this winter than usual as well. Anecdotally as well, but perhaps worth mentioning is the fact that one neighbor has complained of heating bills roughly 30% higher this year than they are used to.
So how did my attic improvements do? Mindful readers will recall that I made improvements to address all three forms of heat flow into my attic:

I used increased convection to let hot air remove itself from the attic, drawing in cooler air behind it. While greatly helpful in summer, this certainly seems like it might hurt my wintertime energy situation by making the attic cooler.
I used a radiant barrier to reflect radiation of the sun's rays back out through the roof, before it could heat up my insulation and eventually my living space. Unfortunately, the heat of the sun's radiation is awfully nice to allow in during the winter. Fortunately, there is a potential upside to the barrier in winter: heat radiated from the top of my insulation in the attic will reflect off the barrier back down into another part of the insulation, warming it.
I addressed conduction from the living space to the attic by at least doubling, and in places tripling the amount of insulation present, bringing my house up to current building codes at least in the area of insulation. This improvement should have helped in the winter as much as in the summer, if not more.

So how did the attic perform? The simplest measure would be just to compare my yearly energy use (regardless of weather changes) for the last 4 years, so that is what we'll do first. I prefer to compare actual volume of gas burned rather than the energy cost in dollars because the price of natural gas is notoriously volatile, making meaningful comparison over time difficult; plus, of course, Energy Efficiency Man cares most about saving energy! So without further ado, here is the wintertime natural gas energy usage graph:

The natural gas usage is measured in "ccf" where 1 ccf = 100 cubic feet of gas.
As you can see, at first it appears that some combination of cooler weather and/or attic improvements have increased my natural gas usage slightly for this winter. But by how much? From our previous weather graph, we know that this winter was about 30% colder than last winter... but my gas usage is only up a few percent (from the numbers, about 2.5%) from the previous year. In fact, although this was by far the coldest winter of the last 4 years, the natural gas usage is below the average usage of the last 4 years by about 7%. This bodes well, and perhaps calls for another graph!
The best thing to look at is probably the heating effectiveness: that is, how much cold a given unit of natural gas can offset; or more precisely, a graph of coldness per unit energy expended. This would simply be a graph of the ratio of HDDs (coldness) to natural gas usage, with a bar on the graph for each winter season. The higher the bar on the graph, the more HDDs a given unit of natural gas was able to handle, and thus, the better heating effectiveness of the house at that particular year. Here we have it:

From the graph, it would appear that we can draw a number of interesting conclusions about the performance of the house in wintertime.

The attic improvements between the winter ending on 2007 and the one ending in 2008 (the rightmost two bars on the graph) caused a slight decrease in the heating effectiveness of the house. In fact, spring of 2007 is when I greatly improved attic ventilation, but didn't do anything else. That must have resulted in the roughly 3% drop in heating effectiveness by letting more cold air into the attic. That is a price, albeit a small one to pay for the roughly 15% drop in the electric usage experienced that year.
The attic improvements between the next two winters, ending 2008 and 2009, improved the heating effectiveness of the house by about 9%. That was when I installed the first half or so of the radiant barrier, as well as replaced the broken air conditioner (which also could have effected the heating system). This is the only chance we have with my house to compare winter performance without a barrier and with one; unfortunately, it's only about half of the barrier that was installed. I for one am pleasantly surprised to find out that the barrier seems to have actually helped in the wintertime, in addition to helping greatly in the summer. I say "seems to have helped" because the change to the air conditioner/blower unit could also have affected the efficiency of the heating system.
The final comparison, between the winter ending in 2009 and the one just about ending now in 2010, shows the true power of attacking all forms of heat transfer at once. Finally in 2010 we've got the full radiant barrier installed, we have good ventilation, and we have lots of new insulation. The result: a dramatic improvement in heating effectiveness. The house now heats itself roughly 30% more effectively than it did last winter, and 38% more effectively than it did before all the improvements began. It would appear that the mysterious winter coziness that I wrote about this winter was indeed something very, very real.

The verdict is in: the summertime-focused improvements, which we feared might have negative consequences in the winter season, have actually yielded wintertime savings as well... significant ones. Coming soon: a revisit to my investment percentages / payoff time calculations in light of the long-awaited wintertime analysis.

But until then, adventurers in Energy Efficiency, stay warm and stay efficient!

Mysterious Winter Coziness

2010-02-23T20:50:00.000-08:00

Careful readers may recall my concerns that my radiant barrier is going to cost me some much wanted solar heating during the winter. While this is undoubtedly true during the seemingly rare sunny days this season, as this winter progresses I get the feeling that the effect may be pretty well balanced out by other effects of the improvements during the cold nights. While not easily definable, the house does seem to have more "coziness" than in previous years, especially given the long runs of cold temperatures we've had this year.

Given that my thermostat is set at the same temperatures that it was before I finished my attic improvements, how is it possible that the house would feel different now? Isn't 68 degrees 68 degrees? Well, yes and no. Your skin senses more than just the air temperature, although that is a major factor. What your skin really senses is energy: specifically, the amount of energy being absorbed by the skin or leaving the skin. The balance of that energy is what matters.

If you have read this blog for any length of time, you know that there are three modes of heat transfer: convection, conduction, and radiation. Convection matters only for your breathing, which unless you're in a sauna or Texas in the summer, acts to cool the body as the exhaled air carries heat from your lungs out into the environment. One might argue that this is really conduction, in that the heat conducted out of your lungs into the air, but we will not delve further into metaphysical hairsplitting than that. Suffice it to say that the rate heat flow from breathing is proportional to the difference between the temperature of your lungs (your body temperature) and the air temperature. Since my thermostat setting hasn't changed from pre-improvement house until now, convection cannot account for the difference that I feel in the warmth of the house.

That leaves two modes of heat transfer in and/or out of the body to discuss. First, the one everyone knows about is conduction. Your skin's contact with the air, or any other surface, that is cooler than your skin temperature causes heat to conduct out of the skin and into the air. The heat flow from conduction will be a rate affected only by the amount of clothing around the skin (which acts just like insulation and slows the heat flow) and the temperature difference between the body and the air. Since I still tend to wear sweatshirts around the house, and my air temperature (a.k.a. thermostat setting) hasn't changed, conduction can't be the difference in coziness that I'm feeling.

The final mode of heat transfer is one near and dear to my heart: radiation. The fact is that your skin absorbs radiated energy very well and warms nicely because of it. Why do you stand in the sun on a cold winter day? "Well, the air is warmer in the sun", you might reply. Is it indeed? What if the wind is blowing? Suppose that air that surrounds you in the sun just blew in from under the trees, where it's shady. In fact, the air in the sun tends to be the same temperature as the air in the shade (at least as a first approximation; over time, if the air isn't moving, it will warm, of course). Instead, _you_ are warmer in the sun, but the air is not. You are warmer because your body is a solid object, which makes a nice "brick wall" for all those energy-carrying photons from the sun to run into. Your body, in fact, will absorb a lot more of the sun's energy than the air around you, because that air is mostly empty space and most of the photons "miss" the air molecules as they pass through.

What does all this have to do with my house feeling cozier? Well, you've probably figured out that it has to do with radiant energy, since we've eliminated the other two forms of heat transfer. This is indeed the case. But what mysterious object inside my house is radiating that energy, and why has it changed from previous winters to this one?

Before I answer that, we all need to remember that every object that contains heat radiates that heat in the form of energetic photons. Some objects are better at it than others, depending on their surface characteristics and their temperature, but stated scientifically, any object with a temperature greater than 0 degrees Kelvin ("absolute zero" or -273C) will lose energy or "cool itself" by radiation of energetic photons, typically in all directions. The wavelength ("color" if it falls in the visible spectrum) of those photons depends on how much energy they contain: the longer the wavelength, the less energy. Most objects around us every day radiate heat in the infrared spectrum; that is, at an energy level below what the naked eye can detect. However, given some nifty infrared "night vision"-type goggles, one could easily see everyday objects obeying the laws of physics, dumping out energy from themselves in the form of photons. Some particularly hot objects like a hot coil on an electric stove might get energetic enough to put out photons that cross from the infrared (Latin for "below the red") up into the visible red spectrum, which, of course, is why that hot coil would glow red to the naked eye.

Once again, let us return to the house being cozier this winter. Some fraction of the energy balance entering and leaving my body in a given instant must be from these infrared photons slamming into my skin, warming it up ever so slightly. (Or, perhaps more precisely, hitting my clothes and warming them slightly, causing less of a temperature difference between my clothes and skin, thereby reducing the heat conduction). Those photons must be coming from all the objects around me inside the house, even as I sit here typing this. But what photon-radiating objects would be radiating MORE photons this year than they were last year, making me feel cozier?

Well, since we're tracking down a change in behavior, let's see what circumstances changed that might cause it. The improvements I made to the house were all in the attic. And the surface of the room I'm in that is connected to the attic is... the ceiling! Is it possible that the ceiling is radiating more photons down into the room than it did last year, warming me and making me feel cozy? If so, what would make it do that?

Indeed, the energy imparted by energy radiated from an object like my ceiling is greatly affected by its temperature. In fact, the exponent in the relationship is 4, meaning that a doubling of the absolute temperature gives you 16 times as much radiated energy (2 to the 4th power). Now, is it possible that my ceiling is staying warmer than it was last year?

It is certainly possible and indeed likely. However, I did not have the foresight to measure the temperature along the ceiling before I made the improvements, so even if I devised a way now, I wouldn't have two numbers to compare.

But research, logic, and the above reasoning do tell me that the increased coziness has to come from there. The fact that I added significant insulation above the ceiling in question, doubling it at least, should tend to keep it warmer in the same way adding a blanket on top of your body on a cold night keeps it warmer. Add to that the fact that the top of the insulation, facing up into the attic airspace, will now radiate its own energy directly upwards into a newly completed reflective radiant barrier, which will direct about 97% of those photons back down into the insulation, keeping the insulation warmer and thereby reducing conduction from the ceiling into the insulation above it. In other words, that ceiling really should be warmer.

So, although the jury is still out for another month or so as to whether the dramatic savings I've seen in summertime will appear in winter, or whether my hot-season-targeted changes will hurt my wintertime bills, I can say that the experience of the first cold season under the new attic has led me to notice a definite improvement in comfort.

While we wait for the end of winter and my post-winter efficiency analysis, please enjoy this picture of me in attic regalia assisting a friend in some radiant barrier installation. 'Tis the season for attic work, after all, and as I am sure we never tire of hearing, Energy Efficiency waits for no man!

The delicate balance of airflow

2010-01-28T19:08:00.000-08:00

I've been thinking a lot about attic airflow lately. In the warm, humid climate that I live in, having appropriate airflow through the attic is important in at least two ways. First, it is important because it allows cooler outside air to automatically replace the hot air in the attic. Secondly, it is important because it reduces the chance of condensation, the enemy of all homeowners. How does it do this? By allowing the air to find its way out of the attic as it cools. This particular point may we worth delving into in detail, because many a roll of insulation and many a roof has been lost to the perils of unexpected condensation.

Critical Features of Condensation

Two main principles drive condensation. The first is hopefully known to everyone who attended elementary school: hot air rises. Or more accurately, air that is warmer than the surrounding air is also less dense than the surrounding air, so it is buoyed upwards. This principle explains why we don't hold our hands over candles, why all the nice hot air in your house rests against the ceiling, and why hot air balloons work.
The second is known to anyone who has taken a passing interest in meteorology: warm air can hold more moisture in it than cold air. This little phenomenon explains why cold fronts are often led by a line of rainstorms, how fog forms, and why clouds tend to dump all their moisture when they reach the front of a mountain range. This last one is quite fascinating to me: the surface winds sweep up the mountainside, bringing warm lowland air higher and higher. As the air gets higher (via orographic lifting) it naturally loses pressure and therefore temperature (due to a process known as adiabatic cooling). Once the air gets high enough that it can no longer hold the moisture that it carried before with no problem when it was warmer, the moisture condenses out of the air and falls to the ground as rain.

Now, given these two main principles, we can apply them to attics and see why they can create moisture problems. One side of effect of human activities such as breathing, cooking, cleaning, showering, and so on carried on inside a house is the creation of warm moist air. Thanks to the principle of warm air rising, the warm air we create in our houses moves upwards. Since things like cracks, gaps, and seams exist in most houses, the warm moist air finds its way into the attic.
Once the air is there, if there is not sufficient ventilation to move it out and replace it with new outside air, the moist humid air will stay in the attic, encouraging bad things like mold growth. Furthermore, if the attic cools down quickly like it would on a nice clear fall or winter night, that trapped warm moist air would become trapped cool moist air. If the air cools enough, thanks to our second principle above, it will no longer be able to hold the moisture that it held when it was warm and the water will come out of the air and "rain" (condense) in the attic. Two factors determine the severity of this "indoor rain event". The first is the amount of moisture that was put into the air to begin with, and this can be reduced by good habits like running the vent fan when showering. The second is how far the air cools: the cooler it gets, the more water will be squeezed out of the air. The way to ameliorate this is to have enough ventilation so that as much of the air as possible can escape before it cools down enough to drop its moisture.
If these "indoor rain events" occur often enough in the attic, you will begin to see water damage to your house.

Seasonal Balance

So if condensation is bad and ventilation can defeat it, why don't we just get as much ventilation in place as possible? Why don't we just cut vents in all 4 attic walls, stick screens over them, and be done with it! The mindful reader will recall that the title of this post implies that there is a balance to be achieved here. That balance, like most balances one can achieve, depends on one's place in life. Or more correctly, the place that one lives.
If you live in an area that is almost never cooler than you want the interior of your house, putting in as much attic ventilation as humanly possible is probably the way to go.
If you live in an area like I do, where most of the year is spent with the outside world a lot hotter than I want my house to be, but a good 3 months is also spent with the outside world a lot colder than I want my house to be, I want enough ventilation that I get some good cooling in the summer and good protection from condensation year-round, but I don't want so much ventilation that my attic loses all it's heat-trapping potential for the winter. This is particularly important in my house because a lot of water pipes run through my attic, and an attic that freezes solid in my few freezing winter nights would freeze and burst water pipes over my living space.
I would guess that if you live somewhere that's cooler outside most of the year than you want your house, and rarely much hotter than you want your house, you would want just enough ventilation to avoid condensation problems, but not more than that.

Flow Balance

So have just discussed one axis of balance for our ventilation. There is another axis as well: the amount of space dedicated to air leaving your attic (net free area outflow) should be balanced as closely as possible by the amount of space dedicated to air entering your attic (net free area inflow). Why does this matter? In fact, why do you need any intake at all? Isn't the point just to get that hot air out?
If you've ever tried to pour milk out of a gallon jug, you might have noticed that it doesn't work well if you just tip the jug over so far that the milk just slops out of the jug in series of bursts, interrupted by gasps when you can hear the air rushing back into the jug, almost as if it were taking a breath before dispensing another sloppy burst of milk. Why is it so difficult for the milk to get out? What's slowing it down?
The answer, of course, is lack of replacement air. When a certain volume of milk leaves the jug, it leaves a vaccuum, or more accurately, the air inside the jug is left at lower pressure than the air outside. This causes the air outside to force its way in, interrupting the smooth flow of milk out of the jug, and reducing the speed at which the jug can be emptied. In fact, the best way to really move that milk out of the jug is to punch a hole in the bottom just before we turn it over, to allow the air to come in from the top as the milk empties out the bottom.
Now: if we turn the whole thing upside down, replace the jug with our attic, the milk with hot air, and the opening in the jug with attic roof vents, the analogy makes perfect sense. Bear with me as I explain.
If you just had roof vents in your attic, and did not have any soffit vents, gable vents, or other air intakes, your attic would be just like that milk jug turned upside down before we punched a hole in the bottom. The air would slosh out of those vents as it heated up and tried to leave, but that would create a lower air pressure region inside the attic. This would tend to pull air back in the vents (the only openings), dramatically slowing the airflow out of the attic, just as the inrushing air slowed the milk from leaving the jug.
The solution, of course, is to punch a hole in the bottom of the attic just as we punched a hole in the bottom of the milk jug. That is what soffit vents and other air intakes are: a way to get air to "backfill" for the hot air that leaves through the vents in the top of your attic. The fact that the backfilling air can come in through a different path than the air leaving means that you can get a nice, uninterrupted flow of ventilation through your attic. Plus, well designed intakes will pull replacement air from cool, shady spaces like the underside of the eaves.
Now you might begin to get a feel why the outflow area should equal the intake area. If the intake vents can't supply enough air, the air to make up the difference will try to come through the outflow vents, and the more it does that, the more you mess up your nice smooth outflow, and the less the attic air will be able to escape.
Indeed, attic airflow is a delicate balance.

Payoffs by category

2010-01-14T19:45:00.000-08:00

After talking to some other energy efficiency enthusiasts, I have learned that there seems to be a lot of interest in the financial rate of return for the different Energy Efficiency improvements that I've made. Although I've discussed these things before, it behooves me to say again that my methods are not as rigorous as a true scientific experiment; rather, they are the methods of someone who wanted to improve his Energy Efficiency and has taken some basic notice of the costs and cost savings.

I will include numbers for transportation energy use (which I don't typically discuss here), because transportation by car is a giant user of energy; likely at least roughly equivalent in scale to the energy use of my house. This is why there is much discussion of plug-in hybrid cars being used to feed energy to (and take energy from) houses in the future; they might well carry enough battery storage to be significant in the home environment.

You should be able to click to enlarge the table.

From that table, it looks like the attic efficiency work is paying off rather well at 28%, and probably would be paying off spectacularly well had I not muddied the waters by paying for a bunch of roof decking plywood to be replaced in 2009 so that I could get radiant barrier into some areas inaccessible to me from the attic. The cost of that plywood per square foot was roughly 10 times the cost per square foot of the radiant barrier that I ended up putting on it, which is why that rate of return drops so dramatically :( But I was getting the roof replaced at the time; my next shot at getting the sun blocked from that accursed vaulted ceiling would likely have been 15 years later, so I bit the bullet and replaced that plywood with radiant-barrier (and baffle-)covered plywood, improving radiant barrier and ventilation in one fell swoop.
Some might also judge, from that table, that the radiant barrier (completed in 2009) might not pay off as well as the attic ventilation (completed in 2007, which returns a whopping 51% and has already paid for itself). But you might be wrong in that analysis partially because of the plywood cost that's thrown in to the mix. My gut feel is that the payoff of ventilation (plus duct sealing) vs. radiant barrier tilts slightly in the direction of ventilation, but they're both incredibly efficient uses of your money to save energy. And the comfort improvement with radiant barrier is outstanding.
In fact, with rates of returns this high, you literally should be taking a loan at any interest rate less than 20% and applying it to any of these techniques and making money by doing so. But I will not belabor that point; this is a blog about Energy Efficiency, not Making Money... although since these numbers show we can clearly do both at the same time, why aren't we?

Chronically underestimating efficiency?

2010-01-03T13:47:00.000-08:00

Listen, dear readers, to something that is confusing to Energy Efficiency Man. I often read about energy efficiency measures in the press. Most of the articles written by reporters and policymakers talk about incentives or various combinations of steps homeowners can take, and if they mention numbers at all, they mention numbers like "9% energy reduction" or "20% savings". In fact, I can't recall a single press or government-authored article that I've read recently that mentions a number more than 30%. This New York Times article discussing recently released White House paper on "Cash for caulkers" goes so far as to estimate 28%. Now, as nice as 28% is as a savings, it simply doesn't grab the attention or change the terms of the energy discussion like a number greater than 50%.
However, as readers of my blog over the past few months have learned, I've personally experienced electric energy usage reduction of nearly 60% (in the literally hottest summer ever in Central Texas, mind you), and I've read articles by people who have actually done these things themselves, and the energy savings they typically mention are 50-75%.
My question: why are the people actually saving energy in the real world saving 50-75%, but the folks putting out most of the articles only think you can get 20%? To me, a 50% energy reduction is a game changer. With reductions like that, the current debate in my municipality about what to do with our stake in a local coal plant (which provides only 30% of our energy) becomes entirely moot. What to do about the coal plant? Shut it down - we wouldn't need it, and we don't want the 70% of our emissions that it produces. We could shut it down and still have an additional 50%-30%=20% spare capacity for population growth. (By the way, that is NOT one of the options under consideration by our city council - instead, we will likely spend tens of millions of dollars investing in making the coal plant "cleaner").
Are 50% savings like that too radical to make the press? If all energy users (homeowners, businesses, and governments) could achieve the savings the real-world Energy Efficiency enthusiasts have, we wouldn't need to build another coal plant, ever. We could achieve these energy savings, as I have in the very real world, by investing money borrowed at a typical rate of 5-10% for a rate of return between 20% and 40% according to my own experience. In effect, we could make money by saving energy. And of course, our rate of financial return would go up as the price of energy goes up.
Some of you may be familiar with Factor Four by Ernst Ulrich Weizsäcker, Amory B. Lovins, and L. Hunter Lovins. Energy efficiency enthusiasts will recognize Amory B. Lovins of the Rocky Mountain Institute, a policy think tank on energy issues. The book has been around for over a decade, and in it, the authors argue that based on real-world experience with industry and manufacturers, we are using energy at about 1/4th the efficiency that we could be. In effect, we could be doing 4x as much work as we are now with the same energy, or twice as much work using half the energy we use now, or the same amount of work using 25% of the energy that we use now, based on making improvements that pay for themselves in a manner timely enough to pay off the loan to make them. I would have to say that my own experience makes me think he is likely correct. There are still a few things that I'd like to do to my house that might get me to that magic 75% reduction, and although I've probably gathered most of the low-hanging fruit, there is more fruit to be gathered (probably mostly in replacing windows that are currently inexplicably surrounded by one of the most heat-conductive materials available, a fact which I still plan to discuss in a future post).
So why are we reading about all this work we have to do to save 20% at best, but folks actually doing it are saving 50%-75%? Comments welcome!

Radiant Barriers, simple explanation

2009-12-21T19:26:00.000-08:00

When I talk to a lot of folks about radiant barriers, I get the sense that their level of understanding is about where mine was five years ago. They sort of get it, but they sort of don't. Energy Efficiency Man knows that blocking this particular form of heat transfer (radiant energy) is incredibly important in hot climates, and is highly underutilized out there in the USA, costing us lots of unnecessary energy use and reducing our summertime comfort.

So what is a radiant barrier? Put in the simplest terms, it's 100% shade for your house. That radiant barrier is keeping sunlight from heating up your house the same way a huge oak tree that shades the entire roof would. In fact, it's probably doing a better job; depending on the angles involved, that pesky sun is probably sneaking around at least part of that theoretical tree and heating your house at some point during the day. The "shade" from the radiant barrier, the area under it hidden from the sun, moves less during the day since it's right down at the level of your attic, rather than a certain number of feet higher up where a shade tree canopy would be. If you picture the sun moving across the sky and an two objects casting shadows, one tall and one short, you will realize that the higher up (or taller) an object is, the further its shadow is going to move along the ground as the sun crosses the sky. So if you want the shadow to cover your living space for more of the day (and you do!), you want the shading object as low over the living space as possible.
To put it in slightly more detailed and accurate terms, a radiant barrier is like 97% shade (the rating for a good foil barrier), except that unlike the shade tree which absorbs the energy of the light to produce nutrients for the tree, the barrier reflects the energy back the way it came.
Another typical question: "OK, I understand the shade thing, but the radiant barrier is inside your attic. It's already in the shade. Plus, I've read that it can be facing down, and still work. I can see how it would work if it were like a mirror facing up, but if you install it on the underside of the rafters, it's facing the wrong way. How can that even be possible?" My answer? You've got me. I just know it does work, really, REALLY well, and I've got the numbers to prove it! If I were to guess, the simplification most of us make to think of photons as particles that bounce off of the barrier and get reflected probably just isn't accurate enough. Light is also like a wave; perhaps we're talking about a dramatic change in the index of refraction of the medium which is transmitting the photons causing the energy to be reflected (even though the reflective side is facing the wrong way). Comments from folks with real physics knowledge are welcome. One clue as to the physics might be that the radiant barrier needs to have an air gap next to it to operate; in effect, the reflective side must be facing an empty air space of at least an inch, or the barrier won't work.
For me, it's good enough to stick with the shade analogy. Who wouldn't want to put their house in 97% shade, without having to wait 20 years for a good shade tree to grow, to say nothing of trimming the limbs, raking leaves, and worrying about things falling on your house?
If you've read this far, you don't have a radiant barrier, you have less than 97% natural shade on your house, and you live in a hot climate, this post is for you. You know what to do.

Heat Transfer, revisited

2009-12-10T09:08:00.000-08:00

I have thought a lot about how I have managed to reduce my electricity usage by over 50%, with a good bit of that reduction occurring before I added any additional insulation, the one thing people usually think of when talking about home energy efficiency. I think I can boil it down to three major factors, followed by some explanations:

My attic lies between my entire living space and the sun
My attic used to work against me, trapping the sun's energy
My attic now works for me to reject the sun's energy

Let's examine my attic space's performance with regard to the 3 mechanisms of heat transfer (explanation here) before any improvements were made:

Conduction: I had roughly R-20 insulation in the attic, enough to slow conduction somewhat, though far below code. This was probably my "least bad" heat transfer problem.
Radiation: I had a composite shingle roof which gathered the radiant energy of sunlight all day, heating up and then radiating its own energy down into the attic all day and all night, where it heated up the air and the insulation. The energy that hit the insulation turned into heat in the insulation that eventually conducted into the living space, costing me energy to remove via air conditioning. This was probably tied with #3 as my worst heat transfer problem.
Convection: I had very little air intake into the attic since my soffit vents were mostly blocked, and too few outflow vents on the roof, and those that I had were badly placed (not at the peak). Thus, all the air heated up by the radiant energy in #2 tended to stay in the attic for very long periods of time. In short, my attic was working as a rather effective solar oven to heat up a bunch of air, then hold it right next to my living space for a very long time. Again, this was probably tied with #2 as my worst heat transfer problem.

As you can see, in my first 9 years or so in this house, from 1996-2005, I was expending way more energy than I should have needed to, because my attic was working against me in every mode of heat transfer.

Contrast that to now, when through some rather simple improvements, I've seen the following:

Conduction: In this most recent year, I've improved my insulation to about an R-49 level, current to today's building codes, from an R-20 level. This should be helping me reduce conduction gains in the summer (and losses in the winter) by some 50%. Again, my feel is that this is the least significant improvement for summertime (winter is another matter), which is one reason I did it last, but it should be helpful. Another reason to do this one last is that all the insulation gets in your way when you're trying to work in the attic!
Radiation: In the last two years, I completed installing the radiant barrier. Instead of acting to gather the sun's heat and put it into my attic air and insulation, my attic now acts to reject over 90% of the sun's heat right back out through the roof, before it can warm anything other than the shingles.
Convection: By opening more soffit vent intakes and installing a continuous vent along the ridgeline of the roof, I'm allowing convection to work for me to actively cool the attic by replacing air that heats up and rises through the ridge vent with cooler air that is at the outside air temperature. Since my attic routinely got over 150 degrees, and even on hot days, the outside air is around 100 degrees at the hottest, this has been a huge help.

As you can see, rather than having 2 of the 3 heat transfer mechanisms actively working against me (radiation and convection), I have largely stopped radiation, and convection is now working for me rather than against me. These two things alone dropped my yearly electric usage by 50%. The attic insulation that I've added to address conduction should help as well by reducing the magnitude of the conduction heat gain.

All this talk of heat and 100 degree days seems odd right now in December. The temperature outside is in the 40's, and I do wonder what effect the improvements will have on my house's wintertime performance. Too much attic ventilation, after all, will keep that attic colder and will increase my conductive heat flow from the living space to the attic. The radiant barrier, while reflecting any radiated heat from the top of the insulation back down, is also rejecting the sun's rays that would be nice to have during this cold time of year. Both of these factors should be mitigated by the additional insulation I've added. After all, these improvements are a balancing act, hopefully well-tuned to the requirements of my local climate. Rest assured, efficiency enthusiasts, that this too will be analyzed in a few months as data comes in!

Usage Comparison: 2005 - 2009

2009-12-09T21:53:00.000-08:00

Well, the data is all but in for 2009. Although I don't have my electricity usage for December measured (or even completed yet), I can estimate it pretty well because it is consistent from year to year, plus the value is so low since there is no cooling demand that I can be off by a large percentage and it won't particularly change my results. So I'll go with 11 months of real data and 1 month (December) copied from the 2008 data. Here are my results (drum roll please):

As you can see, the usage for 2009 is well below the 2008 usage, even though 2009 was the hottest year here in central Texas, EVER. The improvements that helped lower the usage this year included completing the radiant barrier (which was only about 40% done in 2008) and installing enough attic insulation to bring the R-value up close to the current code of R-49. In all previous years, the insulation was an estimated R-20.
The numbers:
2005 usage = 13866 kWh
2009 usage = 5731 kWh
Reduction for all improvements (read the Executive Summary to see them all): 58%

For just the 2008-2009 comparison:
2008 usage = 6982 kWh
2009 usage = 5731 kWn
Reduction for 2009 improvements (completed barrier, added insulation): 18%

One thing a lot of people focus on when you talk about home energy efficiency is insulation, but as you can see above, from 2005-2008 I reduced my electricity usage by half without adding an ounce of insulation. There is far more to reducing heat flow than adding insulation. Remember, there are 3 ways that heat flows into (or out of!) your house: convection, conduction, and radiation. Traditional insulation addresses conduction quite well, and possibly convection, but it fails miserably at reducing radiative heat gain. Of course, to handle radiation, you need a radiant barrier. More on all of this shortly; I think that a basic understanding of heat flow is critical to the efficiency enthusiast.

Holidays and SIPs

2009-12-09T08:15:00.000-08:00

Apologies to my "multitudinous" followers about the lack of posts lately. The busy holiday season is upon us, along with end-of-the-year business tasks, and time for posting has been reduced. For those who are interested, I'd recommend the following to fill your web-browsing needs:

Diverging a bit from my usual focus on retrofits, I read about a simple construction idea gaining more popularity: using the same materials we already build with, but rearranging them a bit, can produce incredible energy savings. Building with Structural Insulated Panels (SIPs) can reduce energy use of a home by 75%. The trick: instead of a wall studs every 2' connecting inner and outer walls with insulation laid between them, SIPs use a sandwich of foam insulation between "slices" of wood, with the wood facing the inside and outside areas. Building the walls this way, while using roughly the same materials, reduces the number of "thermal bridges" (the wall studs) that provide heat a shortcut around the insulation. Although nominally the same R-value as an insulated traditional wall of the same thickness, there are fewer areas that are far below the rated R-value, yielding a true overall resistance to heat flow that can be 4 times better than the traditional construction. Think of it as averaging fewer zeroes for missed assignments (i.e. the wall studs) into your otherwise good Grade Point Average (the R-value of the insulation), and you can see why it works well. About the only downside seems to be that you _really_ need to keep moisture out, or it ruins the foam/wood bond. Experienced construction people should know how to do this.

Winter: downside of a radiant barrier?

2009-11-29T08:34:00.000-08:00

One thought that has been on my mind lately, with our cold weather fast approaching, is whether the radiant barrier will make it harder to heat my house throughout the winter. One nice thing about living in central Texas has been that, even on the coldest winter days, the sun has enough power to warm the house pretty significantly by afternoon if the day is sunny.
But the radiant barrier rather effectively rejects that radiant energy. This, of course, is a bad thing during the winter, but a really great thing during the summer. The balancing factor during the winter is the fact that a lot of heat that would typically radiate out of the warm attic during the night will be reflected by the barrier back down into the house, keeping the house from cooling as quickly during the night as it otherwise would.
So some questions arise:

Does the radiant barrier help me or hurt me overall during the winter months?
If it hurts me, does it cost me more energy during the winter months than it saves me during the summer months?
How can I find out the answers to questions 1 and 2?

As it turns out, my home is heated by natural gas, and the company was willing to provide my natural gas usage since 2005. So I will be able to perform some analysis.
Just as there is Cooling Degree Day data out there on the web, there is Heating Degree Day data as well.
When this winter is over, I plan to perform a natural gas usage vs. Heating Degree Day analysis, similar to the kWh usage vs. Cooling Degree Day analysis I performed for the cooling system of the house. The graphs generated from that data should help answer questions 1 and 2.
As usual, there will be complicating factors. First, when I finally completed the radiant barrier this spring, I blew in a bunch of extra insulation. That will certainly affect my results, but I don't have a very good way to account for it. Second, there are really only about 3 months of significant natural gas usage in the house: December, January, and February. That is not very many monthly data points when compared to the 5-6 months of significant cooling usage in the summer, meaning that it may be harder to identify trends. Finally, my cooling energy is measured in kWh, but my heating energy (burning natural gas) is measured in "ccf" which is 100 cubic feet, a volume of natural gas (presumably at atmospheric pressure), so we'll need a conversion factor between the two which may carry its own complications.
Despite these difficulties, we should be able to determine in general whether my cooling-focused improvements have helped or hurt my house's heating-related performance.
Stay tuned until after the gas meter is read in February to find out!

Trees and Geezers

2009-11-17T18:29:00.000-08:00

Let's take a quick moment here to point out a basic point about this blog so far. Despite technical discussions about heat transfer and complicated graphs with curves and lines on them, the actual things we're doing to the house are pretty simple. Other than replacing the broken air conditioner, every significant improvement I've made to the house is "geezer tech": something that your grandfather could well have done 50 years ago. This includes things like sealing up ducts, considering attic airflow for cooling, and for the imaginative granddads, perhaps even putting up reflective material to bounce the sun's heat back out. (My own father actually did this many years ago with part of his house, using kitchen aluminum foil ... it must run in the family).

The other thing to point out is that there are other ways of achieving energy savings than actually doing something to your house. One significant factor which I haven't really captured is the effect of the slowly growing shade trees around my house. We started in this house with tiny oaks on the west side of the house, but they had no effect until about 5 years in, when they had grown enough to provide shade over the west-facing kitchen windows in the hot afternoons. The kitchen cooled dramatically that year (this was before 2005, when I started taking data; I shudder to think what _those_ graphs would have looked like). There must have indeed been some good energy savings; shade trees are Nature's radiant barrier.

Another way to save energy, if you're designing or planning your own house, is to use passive solar design, something that was done rather poorly with the layout of my house. Since the sun travels further north (in this hemisphere anyway) in the summer, and further south in the winter, you can put your maximum window area facing south, where the incoming solar energy helps you the most in winter, and hurts you the least in summer. Of course, in my "energy efficient" home, the north-facing wall has 5 times the window area of the south-facing wall, meaning that I've got the exact opposite of what I should for this area. In addition, as it turns out, the positioning of my eastern neighbor's trees gives me great shade in the winter, when I don't want it, and only partial shade in the summer, when I could really use it.
I am still considering planting another tree that would give my east-facing back porch some nice shade in the summer, but who's shadow would miss the house in the winter; a sort of passive solar tree design. Unfortunately, that same tree will likely shade some of my northern neighbor's south-facing windows during the winter, so I need to be careful with the placement.

Anyway, the point of this little post is to remind folks that this isn't rocket science, it's really not all that technical in terms of the actions we're taking, and it's really not all that difficult. A 50% reduction in energy usage doing things that your grandfather probably knew how to do really seems like, well, a no-brainer. Energy efficiency waits for no man! What are you waiting for?

The mysterious number 2.6

2009-11-09T15:52:00.000-08:00

When performing the accumulated Cooling Degree Days analysis, which the mindful reader will recall incorporated the memory (a.k.a. hysteresis) of the system to try to get a better handle on the effectiveness of the improvements, we ran across an interesting, nay fascinating result.
It turned out that a pretty good linear model for the response of energy usage to varying cooling degree days (CDD's) took into account the temperature of the previous month as well as the temperature of the current month. The fascinating part of this was that, when determining how much energy my house was going to use, the temperature of the previous month mattered 2.6 times more than the current outside temperature.
This flies in the face of everything that I had learned about homes and insulation theory, at least before I started down the path of Energy Efficiency enlightenment. How is that? Well, like many of you out there, I had learned that the way to keep your buildings cool was to keep that hot air out, and keep a good thermal wall between the cool inside air and the hot outside air, in the form of things like double-pane windows, thick walls, and thick insulation. This would slow the flow of heat from the hot outside air into the interior airspace. And to be sure, my house is now well sealed and has decent windows. However, if that were the 100% correct approach, then why does my real world data show that some factor other than the current outside air temperature matters more? In other words, if the problem is really hot outside air, why doesn't the current outside air temperature dominate the model? If the traditional insulation theory is valid in my case, why does the temperature of air from last month that's not even around any more account for some 72% of the correlation, while the supposed main problem, hot air currently surrounding the house, accounts for only 28%?

Something is definitely amiss with our theory.

Ruminating on this problem leads us to an inescapable conclusion: in my area, during my cooling season, the main heat transfer mechanism into my house must not be direct convection from hot outside air. The traditional "double-pane window, lots of insulation" approach which attacks the convection problem is quite literally missing 72% of the target.
So how is most of the heat entering my house? Well, we have exactly one clue to help us find the culprit. Since we've seen that greatest determinant of the energy usage in June, for example, is the temperature in May, it must have to do with the heat being stored over time in someplace other than the outside air. Possible culprits:

Heat stored in the ground -- During the course of the typical dry summer here in central Texas, the ground becomes parched and unable to cool itself through the mechanism of evaporation, since there is no water to evaporate. Much of the vegetation also goes dormant to survive, not performing its usual transpiration which might also effect some cooling. The ground is in thermal contact with my house's foundation, and heat could certainly conduct into the concrete foundation, and once there, into the interior airspace via conduction or radiation.
Heat stored in all the thermal masses around my house -- Neighboring houses (all of which have nice heat-storing brick sides), sidewalks, and streets all store heat during the day, and radiate so much of it that it is noticeable even to the casual observer walking by after sunset. That radiated energy will be coming into my house from low angles and thus will unfortunately avoid my under-the-rafters radiant barrier.
Heat stored in the thermal mass of my own house -- The bricks on the outside walls certainly store a lot of heat, and that heat can conduct or radiate into the interior of the house. The attic itself consists of a lot of wood and some metal as well as insulation, all of which can and do heat up and store that heat over time, again conducting or radiating to become a problem.

As far as which of these is the most significant, it is difficult to say. I have not seen any indication from other web sources that heat conduction from the ground into the slab is a big problem; it may well be that down at the bottom of my slab, several feet underground, the ground is not particularly hot. (Some data on soil temperature variation with depth in my area would be nice, if anyone can point me to it). However, all that concrete would certainly store a LOT of heat. Unfortunately, now that the house is built, I don't have any good way to insulate between the foundation and the ground, or between the foundation and the interior space. I have heard of foundation insulation during construction, but all the examples I have seen so far are in much colder climates, attempting to reduce heat flow out of the house rather than into it. Furthermore, I have no low-energy means to cool the foundation itself.
To address #2 and #3, having a radiant barrier in all the walls and windows would go a long ways towards reducing the heat gain there. Even my own bricks could be separated via a radiant barrier from the interior space, keeping their significant heat gain from being a problem on the inside of the house. I would be interested to learn how much heat gain is radiating in through my windows, and how much through the walls. There are "low-e" (emissivity) coatings that can be added to existing windows, and I suspect those could be a significant help to me.
Unfortunately for #3 (the heat stored in the thermal mass of my own house) since my house is already built, it would be prohibitively difficult and expensive to rip open the walls and install foil barrier there.
So with this analysis we have identified 3 possible culprits for the main predictor of the heat load coming into the house, and only one of them can be partially addressed as a retrofit project: the radiation of heat in through my windows from nearby sources. The others needed to be addressed in construction, and it is now too late for that.
Well, now that the attic is pretty well taken care of, our analysis of that mysterious 2.6 factor seems to be pointing us in the direction of windows. And so let us begin to follow this new trail; let us examine and look into the efficiency of windows, and how to improve it, soon...

Summer 2009: Vaulted Ceilings Saga continues

2009-11-08T15:24:00.000-08:00

So the weekend before the roofing crew was to show up, I needed to create roughly 16 pieces of 4'x8' decking, covered with radiant barrier foil and properly spaces baffles, to be ready for the job the following week.
As luck would have it, illness struck that weekend, but even in those early days, I knew that Energy Efficiency would wait for no man(!), and I toughed out the job of moving those rather awkward pieces of decking around and working on them. The job was made easier by the fact that the radiant barrier was already 4' wide, making it a matter of a single measure and cut operation to get the barrier on each piece. To cover 8' of length with baffles required 4 baffles per decking piece, but again, that was fairly simple and required mostly eyeballing with a little measuring.
Finally, it was the next week, and the crew arrived. I couldn't sit inside and just hope that the new decking was installed properly; I had to go out and see it. Although they wouldn't let me up on the roof, I was able to assist with a few things like cutting decking for odd-shaped areas near the corners of the roof, and creating 2 or 3 more pieces of radiant barrier decking since the original estimate had been a little low.

Preparing to staple baffles to a new piece of decking

The roofing crew was quite competent, and despite the July heat they completed the job in a single day. My hat is off to them for their professionalism in dealing with a job that had a few more components to it than usual. Here is a shot of one of the last pieces going on to the back roof. The baffles and radiant barrier are facing down, of course, but they are there. You might be able to tell that we had to go two 4' widths in from the outside wall to make certain we had enough length to cover the vaulted ceiling portions, as well as to get above the level of insulation in the attic so that the open end of the baffles inside the attic would be clear.

Later that night, it was clear that the new barrier had helped, although the change was not as dramatic as adding the initial barrier; after all, we were adding roughly 600 square feet to an already existing 1500 or so square feet. Significant, but not as much as going from 0 to 1500 square feet the first time.
This improvement yielded us the following benefits:

600 square feet of radiant barrier
Far better barrier coverage over the master bedroom (from 70% to 100%)
Significant improvements to the intake ventilation
600 square feet of new decking to replace worn (admittedly still functional) decking

The overall cost was around $700, $540 for the plywood decking and around $150 in materials (baffles and foil barrier) making the roughly $1.20/square foot cost of this improvement the most expensive per-square-foot change that I'd made. Again, I balked at doing it initially due to the cost, but I thought that I would regret it over the next 15? years until we got our next new roof if I didn't do it. The improved airflow and ventilation coverage seemed worth it.
The benefits from this job are already pretty well accounted for in the analysis of the 2009 energy data here since this change occurred in July of 2009. I am considering trying to examine 2009 May and June, before the change, with July-September, after the change, but that might not prove very conclusive given the short timescales.

In the meantime, the number 2.6 has been on my mind, and its significance might require some more discussion. Until next time!

Summer 2009: Finally addressing vaulted ceilings!

2009-11-08T14:20:00.000-08:00

After a few posts on analysis, we are returning to the narrative of what changes I made to my inefficient house to achieve dramatic savings and comfort.
After the early spring completion of the radiant barrier and the subsequent installation of a good chunk of blow-in insulation, my attic efforts were largely complete. The only remaining concern nagging at me was the fact that around the border of roughly half of the house, I had vaulted ceilings that were inaccessible from the attic as well as from the outside. There was no way, short of removing roof shingles and decking and attacking from the top, to install radiant barrier in these areas.
This was somewhat unfortunate, because this was a good 4 feet of ceiling along the outside wall that I could not cover, extending around half the house. Furthermore, two runs of vaulted ceiling intersected over the master bedroom, making that room at best 70% coverable with radiant barrier, unless one were to do something dramatic like replace the roof.
Well! As it happened, a (rather convenient) massive, record-breaking hailstorm occurred in March. The damage from that particular storm damaged roofs in my area severely enough that crews are _still_ in our neighborhood replacing roofs, lo these 7 months later. In fact, they are all over this part of town. (And, in a development near and dear to all of our Energy Efficient hearts, a lot of the new roofs I see are getting ridge vents installed. I do not know if they have investigated clearing their soffit vents or not: perhaps some of them will read this blog and know what to do.)
So, although the insurance deductible payment was not trivial, this turned out to be the year to get a new roof. And of course, since this roof replacement event happens less than once a decade, I wanted to take the opportunity to try to make my changes to the decking over the vaulted ceiling areas.
From the beginning I learned that this was unlikely to be as cost-effective as the other improvements that I had made, mainly because I would be forced to replace existing material in the house rather than simply add to it as I had until this point. The material I had to replace was roof decking; there was no practical way to bring up the old decking without tearing it up. In effect, the extra cost I was paying was because I was giving up decking that probably had another 10 or 15 years of life on it.
The deal I reached with the roofer, who was quite helpful, was this: The new decking was going to cost me roughly $1/square foot. Since he couldn't find radiant barrier decking in the exact thickness to match my existing decking, he was going to supply me with the new decking the weekend before the job. Since I still had plenty of radiant barrier left over, I would construct homemade radiant barrier decking by stapling sheets of radiant barrier along one side of the 4' x 8' pieces of decking. Then the crew would remove the existing non-radiant-barrier decking from the parts of the house that I showed them, and replace it with the new homemade radiant barrier decking. The only cost to me would be the cost of the new decking, which I felt was more than fair.
Another helpful thing about replacing the roof decking is that it would help me resolve another problem that had dogged my attic from the beginning: lack of intake ventilation. As you may recall, I had unclogged all the soffit vents that I could reach from the attic. However, there were many places, all of them over vaulted ceiling, where the vents were still blocked due to the impossibility of getting my body in front of the area to work. Replacing the old decking gave me access from outside, allowing a chance to install baffles on the bottom of the new decking to create airflow where there had been none before.

4'x8' decking with baffles and foil barrier

You can see from the picture above that the combination of radiant barrier and baffles works quite well! I had first stapled radiant barrier to each piece of decking (except the last couple of inches on either end, which were going to be nailed to rafters anyway), then stapled baffles over the top of these, spacing the baffles to where the parts flush to the decking would coincide with the rafters.
To review our radiant barrier theory, the radiant barrier needs an airspace adjoining it to work; having it touch insulation or anything else destroys its reflective properties (recommended is at least a 3/4" space; these baffles gave about 1"). The baffle serves to create that needed airspace. In addition, the airspace is creating a channel to allow outside airflow into the attic from the soffit vents, cooling the attic during the evening hours when the barrier isn't helping. Thus, these cheap Styrofoam baffles perform double duty, allowing the barrier to reflect heat out before it causes trouble, and cooling the heat that does get through by enhancing attic airflow. They are truly an excellent value to the discriminating Efficiency Enthusiast!
The only downside is apparent from the photo: each baffle has a couple of inches running down the edge and through the middle that touch the barrier. These are necessary to give you a place to staple the baffle as well as to provide structural support, but along these runs, the radiant barrier will not work due to lack of adjoining airspace. So for each of these pieces of decking with barrier and baffles, I am probably getting only about 80% of the reflective power of the barrier. Still quite worth doing. I even considered trying to install small strips of radiant barrier along the top of the problematic portions of the baffle, but that would have been a good bit of work for very little square footage of reflection, plus, depending on how much the insulation bent under the pressure of the baffle, these sections might have contacted insulation anyway after installation, making them nonreflective. So I left the decking as you see it in the photos.

Take 2: Characterizing Hysteresis

2009-11-05T12:41:00.000-08:00

In my last post, one of the caveats about my results in determining cooling effectiveness was that the real-world data shows hysteresis, or memory, which makes determining the effectiveness of cooling difficult if it the calculation is based only on the temperature outside.
I have attempted to take into account some of this memory by replotting the energy use (kWh) vs. Cooling Degree Days (CDD) data, but with the following change: the CDD numbers on the X axis are the sum of the current CDD value added to a factor times the previous month's CDD value. For for a given month on this plot,

Accumulated CDD = (Factor * previous CDD) + CDD for this month

I utilized the Standard Error function in Excel, STEYX(), to assist me in determining the value of "Factor" by trial and error. I chose a value for "Factor" that minimzed the total standard error of the function; i.e. the sum of the errors of Y as they can be predicted by X. In another intriguiging twist, this yielded a value of greater than 1; in fact, a value around 2.6 actually worked best.
What does this mean? This means that last month's weather matters a lot more (2.6 times more) than this month's weather in determining how much heat is going to entering my home. Another fascinating result, suggesting that once again, simple air convection or conduction (represented by this month's CDD) through the exterior of the house has a lot less to do with cooling load than radiation of the hot environment around me (represented by last month's CDD). Another argument for full-house radiant barriers, if anyone is listening! In fact, the low-emissivity ("low-e") coating on modern windows helps perform exactly that radiant barrier function, but on the sides of the house, somewhere that my attic-based radiant barrier doesn't cover, and something I hope to learn more about in the future. So far, replacing windows has been off of my list due to cost constraints (my entire radiant barrier cost a lot less than 1 window), but there are efficiencies to be gained there as well. But I digress...
I actually also tried this model with a second factor multiplied by the CDD from 2 months ago, but trial and error yielded almost no impact: the factor was less than 0.1. This indicates that the main factors are (in order of importance) last month's temperature, then this month's temperature.

You'll notice a few things right off the bat:

The "best fit" lines look a little high. The reason: I made them fit starting at 500 accumulated CDD; I considered everything to the left of that as noise. So the slopes should match the hottest (right hand) part of the curve well, even if their level looks high. The slope is what I'm after; we're going to ignore the intercept (height) of the lines.
If you compare to the previous 2005 graph, you'll see that the effect of using accumulated CDDs has been to turn the large loop of 2005 data into a double loop, with a crossing in the middle. Intuitively that makes sense: that minimizes the error between a line drawn through the middle of the loop and the loop itself. The standard error for the raw 2005 CDD data was 564; the standard error for accumulated CDD data is 473, a significant improvement, meaning that a line fits this data better (although clearly still not great!)
If you compare to the previous 2009 graph, you'll see that the effect of using accumulated CDDs has been to turn the small loop of 2009 data into almost an exact line. The fact that it's a nice fit for the line means that the house's response to temperature has become much more linear; the "loopy" nonlinear part only appears far to the right in the hottest areas. The standard error for the raw CDD data for 2009 was 141; for the accumulated data, it drops to 95. Looking at the graph, you can see that the best-fit line matches quite well.

So now that we've got a better model, particularly for the 2009 data, how do the slopes compare? We've got a slope of:
2005: 0.99 kWh / accumulated CDD
2009: 0.27 kWh / accumulated CDD

Taking reciprocals to convert to effectiveness:
2005: 1.01 accumulated CDD cooled per kWh spent
2009: 3.73 accumulated CDD cooled per kWh spent
Effectiveness ratio: 3.7 to 1
Conclusion: when taking the hysteresis of the system into account, our home improvements look even better. Rather than a 70% improvement in effectiveness based on the immediate CDD method, I may well be looking at a 73% improvement based on a more accurate model.
While not a massive change, this analysis makes me feel a bit better in that I've now accounted for the rather obvious hysteresis in the data, and come out with pretty similar numbers.
There remains the lingering question of the nonlinearity all through the 2005 data and at the very far right of the 2009 data. It would appear that when things get hotter than the house can handle (which seems to happen immediately in 2005, but not until about x=2000 accumulated CDDs in 2009), energy use gets bumped up nonlinearly. There are probably good physics reasons for this nonlinearity, but I will leave it to my readers to write in a let me know what they might be and how I might model them - or even better, prevent them!
In the meantime, this diversion into analysis was fun, but we still have a little bit more story to tell about the home energy efficiency projects completed in 2009. Stay tuned!

Cooling effectiveness: check!

2009-11-04T14:32:00.000-08:00

I will repeat from my last post:

The energy cost of cooling my home 1 degree has dropped 70% due to my efforts.

Energy efficiency enthusiasts, be enthusiastic! This is an incredible number. Every kWh of energy I run through the air conditioner cools me 3.4 times more effectively than it did in 2005 when I embarked on this journey. And, in a big Energy Efficiency Man plus, almost none of the improvements that brought me these savings will break, wear out, or require maintenance. Ridge vent? No moving parts. Baffles and soffit ventilation improvements? No moving parts. Additional insulation? Will last the lifetime of the building barring roof leaks. Radiant barrier? It's foil hanging from the rafters, folks. The business end is the reflective side facing down, and it won't even get dusty after decades up there.
Yes, the more efficient A/C unit will wear out, but I have little choice but to have an A/C unit of some type here. It is definitely the weak link, and will undoubtedly give me trouble, but it's awfully nice to have when it's 100 degrees in September.

Caveats:

This estimate is based on a linear analysis with a simple "slope-intercept" fit. A better analysis would take the hysteresis of the system into account.
Your mileage may vary: these improvements work quite well in my 5-month cooling season-dominated climate. Effectiveness of all improvements depend on your climate and house situation.

The above notwithstanding, the data (and energy bills!) clearly show much less dependence of the house on the outside temperature as was true only 4 years ago. Truly, the house is cooler to live in as well as easier to cool through most of the year.

Analysis: Effectiveness of Ventilation + Barrier

2009-11-04T13:57:00.000-08:00

I will continue the analysis of the cooling effectiveness of my home, skipping forward to 2009. The improvements in 2007 (related to ventilation) have been enhanced by the addition of a foil radiant barrier and a 14 SEER air conditioner (to replace the failed 11 SEER unit).
Here is a graph of energy usage vs. Cooling Degree Days (CDD's, see previous posts for explanation) for 2005 and 2009. Since 2009 isn't over yet, I have substituted 2008 data for both November and December, but neither of those months is real significant for cooling costs.

Again, as in the previous post, the hysteresis of the system is quite apparent.
As expected from personal experience, the 2009 loop extends almost 100 CDDs further to the right than the 2005 loop, indicating the record breaking HOT summer here.
The curve for 2009, while showing some positive slope, looks almost unfazed by the increasing heat.

So at a glance, it appears that adding the radiant barrier and more efficient air conditioner to the already improved 2007 system has helped. But how much? Let's perform our linear best fit again and look at the results:

Including the numbers from our last post covering 2007, here are the final results of this analysis method:
2005 Slope: 2.8 kWh/CDD
2007 Slope: 1.1 kWh/CDD
2009 Slope: 0.84 kWh / CDD
So, by 2009, the effectiveness of my cooling system has increased again. Stated as "kWh of energy to cool 1 CDD", the effectiveness has gone up from:
(1/2.8)= 0.35 CDD per kWh expended to
(1/0.84)=1.19 CDD per kWh expended.
Finally: something meaningful to compare. Stated as simply as I can, based on linear best-fit analysis to remove weather dependencies:

The energy cost of cooling my home 1 degree has dropped 70% due to my efforts.

The Analysis Continues: Effectiveness of Ventilation

2009-11-04T13:04:00.000-08:00

So given that I have energy usage data, and "cooling degree day" (CDD) data for the summers since 2005, I should be able to determine a correlation between the two, and figure out how much my improvements have helped me while eliminating the variations in the weather. I want to know: how much of my energy savings in 2007 was due to the cooler weather, and how much was due to fixing the ductwork and improving the ventilation?
To answer that question, let's take a look at a graph that plots what I'm interested in (energy usage), vs. the thing that I thing most influences it (CDD's) for both my starting year 2005, and the year we're analyzing, 2007. The graph below has been smoothed by Excel to make the curves easier to follow.

What a fascinating result! The larger, blue "loop" is the 2005 data, and the smaller "green" loop below it is the 2007 data. A few things jump out immediately:

The relationship between kWh and CDDs is not as simple as might be hoped
As expected, the green loop does not extend as far to the right, since a cooler summer caused there to be fewer CDDs in 2007
As expected, the green loop does not extend as high as the blue loop, since we know we used less energy in 2007
The graph indicates a hysteresis, or memory, is at work in our system. We know this because for any given X value, there tends to be more than 1 Y value, and you would need to know more about the system to determine which Y value to use.

In fact, intrepid readers, we have already learned something about my house as a physical system: it has a large amount of memory/hysteresis with regards to outside temperature and energy use. The reason for this seems pretty simple: the house itself, along with everything around it, has heated up more at the end of the year than at the beginning. Thus, even for the same number the CDDs, I must expend more energy to remove all the heat from the house at the end of the summer than at the beginning. Restated, it costs me a lot more to cool the house on a 100 degree day in August than it does on that same 100 degree day in May.
We learned all that from simply looking at the graph! Truly, a picture is worth at least 1000 words.
To verify that the hysteresis is caused by what I think it is, I should be able to look at the raw data and determine that for each year, the lower half of the curve occurs in January-June, and the upper half in July-December. Wondrous to see, I have looked, and it does indeed. If you follow the data points making up each year, you start at the left in January, move across the bottom of the loop going rightward until about the peak is reached in July or August, then move back across the top of the loop during the last few months of the year.
One thing that this complex graph tells me is that it won't be fully accurate to just estimate a slope for each of those loops and compare those slopes to determine the effectiveness of my home improvements to 2007. Nevertheless, I can do it, so I will. Again using simple features in Excel, I come up with the following "best fit" lines for each loop.

Looking at the slope of each of these "best fit" lines will give me a rough idea how well my improvements in 2007 had improved my situation regardless of the weather changes. The numbers?
2005 Slope: 2.8 kWh/CDD
2007 Slope: 1.1 kWh/CDD

This is yet another fascinating result! To the extent that it is accurate, I had already increased the energy-effectiveness of the cooling of my house by some 60% in 2007, yet my energy usage had dropped only some 43% over the same time. Perhaps that makes some sense: I had only improved the cooling-related energy use, and not any other aspect of energy use. Since the cooling-related energy use was reduced due to the cloudy summer in 2007, and that's the only part that I optimized, perhaps the overall savings should be less than 60%.

However, this analysis remains unsatisfying. Looking at the 2nd graph above, the linear fit is just a really poor estimate of the actual function we're graphing. Clearly, the memory at play in the system is significant, and perhaps I can find a way to account for it.

In the meantime, I need to finish the analysis to account for the radiant barrier added later in 2007 and 2008. Read on to fulfill your curiosity!

Analyzing Usage and Weather

2009-11-02T13:06:00.000-08:00

I located some logged online Cooling Degree Day data nicely packaged by these folks.
To review, one Cooling Degree Day (CDD) recorded at a base of 65 degrees, for example, is a day where the temperature averaged over a day was 66 degrees. If the temperature for that day averaged 85 degrees, the CDD would be 20 for that day. Negative CDDs are ignored - actually, they would be counted as Heating Degree Days, which I am currently not using in my analysis (I may at some point in the future when I look at my natural gas usage, which heats my house).
The first question was which weather station to use; there are many in my area, and their numbers are all different. Not _too_ different, but somewhat. I decided to use the airport data since that data has the fewest gaps, even though the airport is a good half-hour drive away, and is well outside the urban heat island that I live on. One of the issues in dealing with long term archived data is dealing with the gaps. In my case, only a few months were missing, and I filled those in with data from another source.
I have the vague idea that my energy usage is mostly driven by air conditioner usage, supported by the fact well known to many Texans that the electric bills are largest in July and August, and are still not fun in June and September. Of course, I'm also using energy for other things such as lighting, computers, televisions, refrigerator, etc. but those loads should not vary as much seasonally, although, in yet another complication, lighting usage varies seasonally as the days get shorter.
So we have some known issues with our analysis, which we can hope will not matter too much:

Location difference between airport (out of town) and house (in town, downwind from downtown in the "heat island")
Small gap in the CDD data filled by data from a different source
Many things sum to make energy usage; air conditioning is only one, albeit a big one
CDD's measurements themselves can be taken different ways. Measuring the temperature every hour, and summing those results over a day, yields a different number than just looking at the (highest - lowest)/2 value that some data providers might use.
CDD's at base 65 might not be the wrong "baseline" for my house. Perhaps my air conditioner does not kick on until the daily average is over 70, for example.
CDD's do not consider sunlight, which delivers far more heat than convected air, particularly on cooler days. It would not surprise me to see some air conditioners running on a day with 0 CDD's but is sunny, and not run on a day with a few CDD's but is cloudy. However, installing a radiant barrier should have reduced this problem for me; I have far less sunny heat gain than before.
CDD's do not consider the non-air environment, except as it affects air temperature. What do I mean by this? Well, a lot of us who live here have seen 100 degree days in May. Although unwelcome, those days never seem so bad as 100 degree days in August. Why? For one thing, there is still moisture in the soil in May. Grass is green and growing, plants are moist and lush, and the ground hasn't been baked for months on end to a nice shade of brown. All of these things will reduce the heat radiating around the area and hitting me and my house, even in high air temperature. In August, on the other hand, the grass is dormant and not evaporating water, cooling the ground. The streets, sidewalks, and bricks in the houses are storing a lot of heat built up over the summer that they didn't have in May. All of that heat is radiated and hits me and my house in August, causing more cooling load, even though very little of it affects the air temperature (particularly the air temperature at the airport, which is out of town).

One way that I hope to discover whether some of these factors matter, and perhaps how much they matter, is to simply graphically look at the data. Do the data make sense? If I graph my monthly consumption in kWh vs. the CDD's for that month, a relationship should emerge if there is one. In a nice, pretty world, it would be a linear relationship, with a slope showing how much energy I need to expend to handle one CDD, but we'll see if that is the case.

Here is a look at the Cooling Degree Days at the airport since 2005. You can clearly see the seasonality reflected, and the amazingly cool summer of 2007 right in the middle of the graph. You can also see how our January's have been getting warmer every year fairly consistently, even while the summers fluctuate, and you can see that the summer of 2009 was all-record-breaking in terms of heat. The graph has been 5-point smoothed (each point has been averaged with the 2 before it and the 2 after it) to make it look nicer.

Attic Efficiency: Check!

2009-10-24T11:22:00.000-07:00

It was February 2009, and I had just finished the satisfying job of adding insulation.
After a quick look around the attic, I finally felt a sense of completion. I had finally covered the 3 major areas that my internet-based education had told me were the major causes of inefficient attics: lack of ventilation, lack of a barrier to radiated heat, and insufficient traditional insulation. It took several seasons of projects, a little bit of money, and the help of some neighbors, but I had finally managed to get my attic into some semblance of energy efficiency.
I am now tempted to attempt to perform a better analysis of how well this has worked for me. Since the only numbers I have used so far have been my electricity usage, I have been unable to account for some known large differences in the weather over the course of my improvements. Without this accounting, the numbers look quite good, as you can see from my previous posts on the subject.
But I have been doing some research into how one accounts for the known temperature differences from one year to the next in ascertaining the performance of one's home. For example, was my energy usage drop from 2006 to 2007 entirely because of the well-known fact that in my area, 2007 was a cloudy and cool summer? Is the fact that my 2008 usage is less than my 2007 usage even more impressive since 2008 was so much hotter?
It turns out that there are some ways to account for this. The concept of "degree-days" is used in conjunction with either heating or cooling. The base for "degree days" seems to be 65 degrees Fahrenheit. The concept is deceptively simple: for cooling, you look at how much hotter the daytime average was than the base of 65 degrees, and you add that number to your total. You continue adding (T - 65) for each of the days you are interested in, until you get a total the represents how much hotter it was outside than inside over the span of time you're studying.
There are complexities about how to best measure the degrees on a given day (the average is not all that accurate; you'd ideally want a measurement every hour or more), and inaccuracies in that heat flow is not always linear (i.e. a 20 degree difference from outside to inside might well be expected to use more than 2x the energy of a 10 degree difference) and there is a baseload entirely unrelated to heating or cooling. Nevertheless, using this method should be an improvement over using no method at all.
As it turns out, there are sources of data out there for Heating Degree Days and Cooling Degree Days for a lot of places out there. There can be holes in the data, which require filling from other sources that may not agree exactly, etc. In addition, there are many schools of thought on how best to utilize the data. When looking at energy usage, one it looking at a sum of many variables, so when looking at energy usage vs. Cooling Degree Days, one will still have other factors unrelated to cooling influence the outcome.
Nonetheless, performing some of this analysis might be instructive. Gird up your brains, faithful readers, for the upcoming analysis is not for the faint of math.

Insulation School

2009-10-24T10:52:00.000-07:00

As luck would have it, the day in late February 2009 that I chose to blow in the additional fiberglass insulation turned out to be the hottest day in months. It was 82 degrees and sunny, yielding an attic that, while cooler than it would have been with no radiant barrier, was definite cause for sweating.
Using the insulation blower was fairly simple, but certainly required two people for any reasonable amount of insulation. My volunteer neighbor stayed on the ground in the garage, wearing an insulation mask and feeding bags of compressed insulation into the blower. The blower, which had a set of rotating paddles inside it, tore up the compressed insulation into small enough bits that they would be blown out through the long hose. I stood in the attic with the other end of the hose, blowing a fine snow of expanded fiberglass insulation a good 15 or 20 feet out in front of me.
We quickly learned a few things:

It takes a _long_ time to feed in a bag of insulation and get it fully blown out into the attic. We had 12 bags, and it took us roughly 8 hours to get the job done. There was some break time to cool down, clear out the machine, etc. but the job was very slow. Perhaps some machines are faster, but ours was pretty slow.
You want to plan your route as if you were a painter; that is, work from the farthest edges back towards your attic entrance, so you aren't "painted into a corner". This helps keep the hose out of the way as well as keeps you from having to traverse over, and compress (which reduces the R-value) the newly blown insulation.
You might also want to plan the various positions in the attic where you are going to stand. As you might expect, the insulation shoots out in a nice arc through the air slowing as it gets further away, with the insulation landing in a nice linear pile under the arc, with most of it landing on the half further away from you. Therefore, you want to fill places that are _not_ right next to you, but are further away. If you point the hose at the floor less than about 10 feet away, you'll just be blowing insulation out of the way with the force of the air, reducing the insulation coverage instead of adding to it. Instead, you want to shoot the air _over_ the area you want to fill, and let the insulation drift down into the area. If you don't understand this, don't worry - you'll learn it pretty quickly as you work.
Since communication is nearly impossible between the hose operator and the machine operator due to distance and machine noise, you'll want to coordinate so that you know when to move to your different blowing positions to get an even distribution. I would ask my neighbor to cut off the machine after 2 more bags, for example, so I would know that I had blown enough insulation in that particular area.
Operating the hose is actually peaceful, almost trance-inducing work. There is a certain beauty (at least to those schooled in the ways of Energy Efficiency) to watching the myriad fiberglass snowflakes dancing down, slowly gathering into giant drifts of heat-flow reducing goodness.

After one afternoon and a brief morning of work, we were done. Another hour or so to clean up all the insulation detritus that drifter around in the garage, and the rental machine was returned. Project complete in less than 1 day!

Completion of the barrier(!) and adventures in insulation

2009-10-22T17:14:00.000-07:00

So as we come to this point in the winter of 2008-2009, I have realized that my attic has a newly found problem.
Problem: Insufficient depth of insulation for current building codes
Solution: Simply add insulation!

At first, I began by buying a couple of rolls of fiberglass insulation. However, after the very time-consuming process of removing the blown-in insulation from an area, measuring the space, cutting the insulation roll, placing the cut piece, then covering that with the old blown-in insulation, I realized I might not complete both the insulation job and the radiant barrier job during the nice, attic-work-friendly cold weather. The installation of the insulation, if you will, was taking too long.

New Problem: Installation of insulation pieces taking too long
New Solution: Rent an insulation blower and blow in more insulation. However, due to the sheer volume of insulation that I planned to add, this needed to wait until I was pretty well done with everything else in the attic.

I completed the installation of the barrier at long last in January 2009. There was much rejoicing in Energy Efficiency Land after that relatively inexpensive but long-lasting project. The total cost of the amount of barrier foil that I ended up using was under $200.00, but the amount of labor was a goodly number of (uncounted) hours over the course of a couple of winters.
After rewarding myself with a few weeks of break from breathing the attic air, in late February I decided to go ahead and try to blow in the new insulation.
The process seemed simple enough:

Estimate the total volume of insulation I would need. I could do this by multiplying the attic floor area by the depth of insulation that I wanted to add. This would only be an estimate, but blowing in insulation is far from an exact science. The bags of insulation at the store should tell me their total volume.
Rent a blower at the hardware store where I would buy the insulation
Arrange the borrowing of a neighbor's pickup truck to carry the blower and the insulation
Arrange the time of another helpful neighbor to feed the insulation into the blower in the garage, while I waved the hose around the attic to distribute it appropriately.

But how well would this go? How long would it take? What new things would I learn?
As usual, read on to find out!

The important Science of Insulation

2009-10-21T21:19:00.000-07:00

As most readers of this blog probably already know, traditional insulation is only a part of reducing heat flow into and out of a house's living area, and should be looked in concert with other means of blocking heat flow such as radiant barriers, and cooling mechanisms like attic ventilation.
Nevertheless, insulation is an important warrior in the heat flow reduction battle whose role should not be taken lightly. In fact, good insulation greatly reduces heat flow from the mechanisms of both conduction and convection, and perhaps even a small extent by radiation as well.
The heat flow reduction properties of insulation are quantified by its "R-value", with higher R-values being more able to reduce heat flow. There's a good layman's description (with full equations and a nifty table of materials) here on wikipedia.
The recommended total R-value for my home's attic when it was built in 1996 was R-30. In terms of my fiberglass blown-in insulation which has an R-value of about 2.5 per inch of thickness, that would mean I should have had 30 / 2.5 = 12 inches of insulation. That actually would have covered up most of the wooden joists on the floor of the attic, but in fact, it did not. The depth of insulation varied, of course, but my best guess as to the average depth was about 9 inches, yielding an actual R-value of 9 x 2.5 = R-22.
So not only was my insulation insufficient for the building codes in 1996, it was now 2009, and we as a society have realized (to some small extent) that we're underinsulating our buildings. The new code seems to be R-49 for my area, which would equate to 49 / 2.5 = about 20 inches of insulation.
So I needed at least 20 inches of insulation, but I had less than half that. What would I do about this discrepancy? And would it keep me from finishing my radiant barrier for yet another summer?
Next: Find out!

Winter of '08- '09: Mission creep part 2

2009-10-21T21:05:00.000-07:00

After experiencing the dramatic cooling capability of even a partial radiant barrier installation, I raised the priority of finishing the barrier over the coming winter. As the weather started to cool, and the fierce Texas sun began to travel south for the winter, leading the Canadian geese and Mexican free-tail bats to warmer climes, I began to spend longer sessions in the attic in an attempt to finish the work.
As I continued to work in the attic installing radiant barrier, one thing that I noticed was that looking around the attic, I could see a lot of wood sticking up out of the insulation, wood that made up the joists for the ceilings below me. This can be a bad sign; typically, as I understand it, one should have enough insulation depth that the wood is pretty well entirely covered. This reduces heat flow from the attic air into the wood, which is important because the wood is in very direct thermal contact with your ceiling. Plus, unless your ceilings joists are _really_ thick, the fact that the wood is showing through means that your insulation is not really very thick.
Now, perhaps some of you are thinking, "what does this have to do with installing radiant barrier?" And you would be right to ask that question. In fact, I had distracted myself once again from the primary mission through another bout of mission creep, this time, to improve the insulation while I was in each particular area of the attic.
Next: read on, to determine what this little diversion into the fascinating science of insulation has to teach us, and learn what efficiencies are in store!

Energy saved by 40% of a Barrier?

2009-10-20T23:18:00.000-07:00

Before we look at the numbers, I should note that it may not be entirely useful to look at the 2008 energy use vs. the 2007 energy use as a measure of radiant barrier effectiveness, simply because I had only installed the barrier over (a bit less than) half the house's total area.
It may well be that installing 40% of a radiant barrier (which is my best guess for the percentage I had put in) does not give you 40% of the performance of a full radiant barrier. Why? Well, for one thing, the radiant barrier concept relies on rejecting heat before it enters the serious thermal mass of your insulation. Having a huge gap in the barrier allowed my insulation to heat up greatly during the day. Why would that be a problem? Because at night, when everything continues to radiate heat in all directions, a lot of the heat radiated by the insulation is going to bounce off the radiant barrier above it and back down into the insulation, rather than eventually working its way out of the house. Thus, a 40% radiant barrier coverage may not give you 40% of the full radiant barrier benefit.
But I have the numbers, so we might as well look at them.

Partial radiant barrier comparison:
-----------------------------------------------
Total electricity usage for 2007: 8056 kWh
Total electricity usage for 2008: 6982 kWh
Energy savings: about 13%

Unfortunately for our accuracy in using these numbers, this was not a controlled experiment, but instead was affected by at least a couple of major changes in 2008. First, the careful reader will recall that the summer of 2007 in my area was the coolest and cloudiest in quite some time, probably depressing the usage numbers for that year. 2008, on the other hand, had a much more "normal" summer with a lot of sunshine and many 100+ degree days.
Second, in late July my old relatively inefficient (11 SEER) air conditioner finally kicked the bucket. Fortunately, I replaced it with a more efficient 14 SEER unit. Unfortunately, the old unit died in a way that made it run more and more frequently over a period of days, working harder and burning more energy to cool less and less.

So considering the difference in weather, the electricity savings of my partial barrier probably saved a good bit more than 13%.
But, considering the fact that the air conditioner got upgraded about halfway through the summer, the electricity savings must be at least partly due to the more efficient air conditioner, reducing the apparent savings from the barrier. Mitigating the air conditioner factor somewhat was the fact that the slow failure of the old unit burned a lot more electricity over a period of days than would normally happen.
It is impossible me to say for certain which of these factors was larger. Suffice it to say that I was impressed enough with the barrier's performance to stiffen my own resolve to spend more "quality time" in the attic over the winter to complete the job.
I will include a look at my total electricity usage for 2005-2008, with 2008 on the left, in case you can't tell :)

2008: The summer of comparison

2009-10-17T11:51:00.001-07:00

Our narrative now winds into the summer of 2008. I had just completed radiant barrier coverage in the attic of a little less than half the house, including a solid section over the east-facing and mostly unshaded master bedroom suite, giving me a very good opportunity to determine whether this formerly hottest area of the house would make a noticeable difference as the fierce Texas summer came on. The other barrier-covered section was west-facing in the attic over the garage.
The first thing that I noticed, as the sun began to warm the house in the summer mornings, was that the air conditioner did not start as early in the morning. In fact, it hardly ran at all before 10 am. This unusual development seemed to indicate that the east-facing "artificial shade" of the radiant barrier was working.
Next, from about 10 am to about 3 pm, the house heated up rapidly. The air conditioner would start to run more and more frequently, as expected, as the barrier located at the eastern and western edges of the house, didn't do much good for blocking the almost directly overhead sun angles. In the late afternoon and early evening I could not tell much difference as the roof and attic were fully heated up, and the air condition ran a lot, although certainly not constantly. The west-facing section may not have helped me as noticeably, first because it was over the garage, and second because I do have partial shade already on the west side of the house.
But how was the feel of the master bedroom, which for more than a decade has been the room that we would avoid in the summer until the last possible moment, due to the heat buildup every single hot day?
The difference was nothing short of dramatic. The hottest area of the house immediately became the coolest area due to the radiant barrier. In fact, for the first few weeks, without ever planning it, we found ourselves retreating to the master bedroom after dinner to read or play on the computer because it was the most comfortable place to be.
Even more amazing was the fact that as the summer wore on and the days got even hotter, we had to RAISE the thermostat setting a degree because the master bedroom was getting too cold. Since the thermostat itself was in an un-barrier-covered part of the house, it was exposed to the full heat load and ran the A/C accordingly. However, the parts of the house not exposed to the full heat load due to the apparently incredible heat-rejection properties of the barrier still received their full measure of cold air from the A/C, dropping the temperature dramatically. I recall at least a 6 or 7 degree difference from the central (uncovered) area to the master bedroom.
These minor miracles were made even more miraculous by the fact that the master bedroom area has two of its four sides as vaulted ceilings, which were inaccessible for installation of the radiant barrier. In other words, this remarkable turnaround from hottest area to coldest area happened with only about 60% radiant barrier coverage of the room. (The only way to get radiant barrier over the sloped part of the vaulted ceilings would be to replace the roof decking with decking that has radiant barrier along the bottom of it, and the only time that it makes any sense at all to do that is when you're replacing a roof (which I in fact did in 2009: foreshadowing!))
In short, the half-done barrier worked incredibly well. The comfort level was immediately noticeable, and resulted in our actually setting the thermostat a degree warmer for that summer. The uneven heating of the house was quite noticeable and caused me a good degree of regret at my late start that winter, and renewed my resolve to complete the barrier over the entire house once the summer heat was gone and the attic was once again safe to work in.

Foil that heat gain!

2009-10-11T15:37:00.001-07:00

After doing my own research, the most effective products looked to me like the industrial-grade foil radiant barriers. The paints seemed a little dicey to me; there were a lot of questions about their effectiveness, and the very best I found looked like they blocked about 70% of radiant energy. In contrast, the foil products were rated well over 90%, with the one I chose at 97% reflectivity.
The questions: how much did I need, and how could I get it installed?
To examine the first question, I first had to answer the second one, because there are 2 accepted ways of installing the barrier.
Method 1: roll the aluminum foil out across the attic floor, on top of the existing insulation. In this case, I would need exactly the (estimated) square footage of the attic in foil.
Method 2: staple the aluminum foil to the underside of the rafters. In this case, I would need a bit of extra foil, to account for the slope of the roof and the inevitable sagging of the material between the rafters.

I estimated the area covered by my attic, including the garage, and multiplied by a factor slightly greater than 1 to account for the pitch of my roof. My roof is a 5/12 roof; that is; 5 inches of rise for every 12 inches of horizontal length. That, if my math was correct, required about 2200 square feet of barrier, assuming I could physically access everywhere I wanted to put it.

The radiant barrier itself, which I purchased from these good folks , came in 1000 square foot rolls, with each roll 4' x 250'. Some vendors also sell them in 2' wide rolls. At times I liked having the 4' width, but at other times, I had to cut the foil width-wise because I needed narrower sections.

Installing the barrier was a long-term process for me. Since I didn't make the decision to start until late February 2008, and we often start getting good sunshine and heat in March or April, I didn't have that many weekends to get it done. Plus, to be honest, some weeks I just couldn't handle the thought of going into the attic again, so I wasn't the most diligent.

Add to that the fact that there is a good bit of setup time for me; I don't enjoy breathing insulation fibers, or feeling them against my skin for that matter, every time I worked in the attic I put on a paper "bunny suit" (painters often use these; you can get them at Home Depot or other similar stores) as well as an insulation-grade mask. Note: in my experience regular masks, like you might use for lawn care or other basic dust applications are not good enough. Wearing a mask rated for insulation use made a noticeable difference in how much distress I felt in my nose and throat after a session in the attic.

Add to that the fact that, since I used the garage as a staging area for rolling out and cutting sheets of radiant barrier as I needed them, I swept the garage pretty much every time I started a session. Why? Because dust stuck to the radiant barrier reduces its reflectiveness.

With all that, you can see that it took a good while to get started each day. Plus, there is cleanup time to put away the roll, change out of the suit, and shower and rinse out your mouth and throat (if you know how to do neti, do so after leaving the attic for the day - it will help knock out a lot more of those unhealthy fibers.)

So, with the late start in the season, and the overhead of each session in the attic, I was able to complete about half of the attic in my first effort. The parts I chose to cover were over the very sunny east-facing side of the house, which included the master bedroom suite - long recognized as the hottest area of the house in the summer - and a portion of the westward-facing area over the kitchen and garage. The entire middle of the house was left uncovered for the oncoming summer.

However, this did give me the chance to experience a summer of comparison; I could compare the feel of the house "under the barrier" vs. the feel of the area without it. How did that go? Read on, and see!

A whole new but familiar concept

2009-10-11T15:05:00.001-07:00

For me, the discovery that radiant energy was a big part of the picture was something big and exciting, to say the least. I was starting to gain an intellectual understanding of something that my body had understood at a basic level for a very long time. I had, of course, felt radiated heat before, and have since learned to recognize it. All of us, from the simplest animals to human beings, know to stay out of the sun when it's hot. Why? Because we heat up in the sun. But few of us actually understand why that is. Why do we heat up in the sun? Because we are absorbing radiant energy. It is not because the air is any hotter in the sun; the air in the direct sunlight, and the air in the shade right next to it, are almost the exact same temperature. Instead of the air molecules bumping into us and heating us up (as most of us learn about in elementary science), a bombardment of photons, a.k.a. radiant energy from the sun, is impacting our bodies and causing them to heat up.
What this means for energy efficiency in the summertime in a sunny climate is this: if you're addressing only the hot outside air, which can affect your home only through the mechanisms of convection and conduction, you are acting like the lone cow out in the field standing in the sun on a 100 degree day, while the rest of the herd is standing in the shade: that is, you are ignoring the most important part of keeping cool.
So wouldn't it be great if there were a way to bounce that bombardment of photons right back into the sky where it came from? Wouldn't that significantly reduce the amount of energy being absorbed into a house, reducing the amount of electricity an air conditioner has to expend to remove that energy once it strikes something and becomes heat? Yes, and most definitively, yes! Enter the radiant barrier.
Officially, a radiant barrier is defined as any material that reflects 90% or more of the energy striking it, which implies that it absorbs less than 10%. There are different types of radiant barriers that you can place at various spots between yourself and the sun, including items as simple as lighter colored shingles, with the lighter color reflecting more of the sunlight than darker colors (although these don't tend to reach the 90% standard to be considered true radiant barriers) to silvered roof decking, to reflective paints, to large amounts of industrial-grade foil.

Onward, adventurers. Physics awaits!

2009-10-03T13:45:00.001-07:00

After that brief detour, where we reconfirmed that energy efficiency is still the way to go, at least until the payoffs for our projects get much lower, let us continue our quest for improvements in the home.
Late in 2007, in my travels on the Web researching energy efficiency opinions, I began to run across a lot of information about something called a "radiant barrier". This was something new to me: a type of insulation that wasn't traditional insulation, and said to stop heat flow in a somehow different, and possibly better way than traditional insulation.
To understand the radiant barriers, we need to upgrade our knowledge about how heat actually flows into a home in the summer, or out of a home in the winter. As I understand the mechanics of the situation (nice explanation here), there are 3 ways that heat flows from a hot area to a cooler area: conduction, convection, and radiation.
Conduction refers to heat flowing through a solid material (such as from the outside face of a brick wall to the inside face), and can be reduced by using materials such as fiberglass insulation that conduct heat poorly; that is, heat only moves slowly through them.
Convection refers to heat moving due to the material (a gas or liquid) flowing through space. This type of heat movement can be reduced by trapping the gas or liquid so that it can't move. In fact, part of how fiberglass insulation works is through trapping air in tiny pockets.
Bear with me, intrepid readers: here is the good part. Radiation refers to the transmission of energy through space by means of photons. Those photons, given off by all hot objects in all directions, travel through the air until they hit something solid, whereupon that solid object absorbs their energy and heats up. If you have ever stood in the sun on a clear day, you have felt the radiation of the sun. If you have ever sat outside at a restaurant with heat lamps, you have felt the radiation of the lamps. That radiation was absorbed into your skin, causing your skin to heat up pleasantly.
At this point, an aside may be in order. For the purposes of Energy Efficiency we are talking about infrared radiation, a certain range of wavelengths of radiation, which is a different range of wavelengths than ultraviolet radiation, the harmful-to-your-skin variety of radiation also put out by our sun.
The savvy reader will have already guessed that "radiant barrier" must refer somehow to the blocking of the radiation mechanism of heat transfer. The savvy reader would, in fact, be correct. A radiant barrier is simply a way of reflecting the energy being radiated by photons through the air, rather than absorbing it.
"But how important can that really be?", the questioning reader might ask. "How much energy entering a house in the summer, or leaving it in the winter, is in the form of photons radiating through space?"
The answer, according to the radiant barrier folks, is a lot. Their numbers: over 90% of the heat gain in the summer comes through as radiant heat. Over 50% of the heat loss in the winter goes out as radiant heat. In short, if you aren't doing something about the radiant heat, you are missing most of the ballgame.
Perhaps at this point, you the intelligent reader is asking, "but isn't my insulation already catching those photons? Don't they travel until they hit something solid, like my house, and then become heat inside a material subject to the rules of conduction?"

And again, you would be correct. In the summer, the radiated energy of the sun is striking the roof of your house. For most houses, only a small percentage is reflected; the rest of the energy is absorbed and becomes heat trapped in your roof (shingles, etc.) At that point, your roof is also emitting photons since it is hot, and about half of those travel down through your attic airspace and strike your insulation, imparting their energy to it, which means, heating it up. At that point, the insulation does its conductive-resistance magic to keep the heat flowing more slowly into your ceiling, but make no mistake: that heat is indeed flowing into your ceiling. From there, some of it is convecting into the inside air, and some of it is being radiated as photons which will strike you, heating you up, and strike objects in your home, heating them up.
In the winter, this picture is reversed. Warm objects in your house (yourself, your furniture, your floor, your walls) radiate photons in all directions, removing energy (heat) from yourself and your surroundings and taking that energy outward in all directions, including up. Some of the ones hitting the walls and ceiling will reflect back, reducing the heat loss everywhere except at the windows; by design, the photons mostly go right through glass. The photons that go up and are not reflected strike your ceiling, which they heat up, and the heat begins to flow via conduction through the ceiling, through the insulation, and into the cold attic where it will either be lost to convection with the cold attic air, or radiation up to the roof and through that, again via conduction, to the outside face of the roof, and from there, radiated out into space.
Think well on these scenarios, adventurers, and be rewarded with a whole new arena of possible energy savings...

How much energy is that, in solar terms?

2009-10-03T12:04:00.000-07:00

Having determined that I cannot afford to hire 20 or 30 people to spend most of their waking lives pedaling bikes to power my house (20 people for 12 hours at $8.00/hr = almost $2000 per day!!!) , I wondered if there might not be other, non-power-grid ways of getting my home powered. After all, Texas is blessed with pretty good sunshine; not as good as the desert Southwest of this country, but well above average. Perhaps I can power my home with solar panels, using some of that energy to my advantage, rather than just fighting it, to reduce its effect of heating my house up through the summer months.

I've got roughly 500 square feet of roof space that might be exposed to enough sunlight for panels to make sense. (This is my estimate; I'd have to get a real professional to look at it for a final number). According to a nice solar system calculator at findSolar, which takes into account the measured sunlight in my area, I might be able to just fit a system into my roof space.
So my electricity needs are solvable with solar, since I seem to have about the required roof space. (I realize that the sun doesn't shine at night; but my house is grid-tied, so I can pull from the grid at night or on cloudy days. I would effectively put energy back into the grid on sunny days where I didn't need all of it; the proposed system is sized to cover my needs as averaged throughout the year, so my net draw from the grid over a year would be 0.)

The solar calculator estimates that the system would cost me around $20,000 (including various rebates and credits). While that's a chunk of change, once I spend it, it covers my energy costs for quite some time. Compared to paying people $2000/day to pedal bikes, this justifies itself after just 10 days. And since panels last for decades (although some of the ancillary equipment won't), this is looking like not too bad a bargain.
So the solar option is clearly better than paying people to pedal. But a more subtle question then arises: is it better for me to spend money buying solar panels, or is it better for me to continue to reduce my energy usage with efficiency measures?
And so we start down the road that most people considering these sorts of things travel: how much do I spend up front vs. how much do I save over time? If I consider $20,000 an investment, what effective interest rate does it pay me? In fact, to know this, I need to know what is the future cost of the electricity it is offsetting, which is, of course, a guess. Like any investment, this "calculation" involves guesswork about the future of the investment, the future of the market, etc.
Looking at what I spent on electricity in 2007, roughly $700.00, the panels might take $20,000 / $700 = about 28 years to pay off in electricity savings, at current electricity prices. That's a return of roughly 3.5%, which is far lower than my efficiency investments have returned. That rate of return for solar will go up as electricity prices go up; however, so will the rate of return on my efficiency investments. So at this point, it's still looking to me like efficiency is the way to go, until I've gotten to the point that the estimated rate of return on those drops to below 5%, or until solar panels undergo another dramatic price drop.

How much energy is that, in human terms?

2009-10-03T11:46:00.000-07:00

As I have wandered through the Web in search of hard information about energy efficiency, I have come to learn a little bit about the scale of energy that is required to run houses as we have built them in my neighborhood. Perhaps some of you have wondered, as I have, if there are not better ways to provide that energy. Maybe I could take human-generated energy, from riding an exercise bike, and use that to power part of my home.
Powering my home for a day in 2007, after my initial set of improvements, required anywhere from 9 to 37 kilowatt hours (kWh) of electricity, with the average being about 22 kWh.

To put that in human terms, when I ride hard on an exercise bike at the gym, I can generate around 100 Watts (0.1 kW), perhaps double that in short bursts, according to the readout attached to the bike. So riding hard for 1 hour, using my body to generate power, would yield 1 hour X 0.1 kW = 0.1 kWh. In fact, if I pedaled all day without drinking, eating, or sleeping, and used that energy to power my home, I would generate 24 hours X 0.1 kW = 2.4 kWh, slightly more than 10% of my energy use on an average day.
To extrapolate further, to power my relatively modest needs, I would need 10 people riding generator bikes 24 hours a day, for every day of the year. Of course, no one could keep that up... to allow for breaks for eating, sleeping, and recovery, I'd probably need 20 or 30 people, pedaling as much as they could stand, every day.
In other words, my energy needs go _way_ beyond what I can provide with human power.

Soapbox, links and taking stock

2009-09-23T08:57:00.000-07:00

Anytime one puts significant time and effort into a project, the question arises: why am I really doing this? Are there not better ways to be spending my time?

There are a variety of reasons that one might have for deciding to work on home energy efficiency. I will detail some of them below, with some commentary of my own.
First and most important for me to this point in the narrative, is that I'm trained as an engineer, and good engineers cannot stand gross inefficiency in a system that they care to optimize. As I began looking into the apparently "standard" way things were done with my house, I quickly realized that efficiency was probably never a consideration; at least, not any more than the building codes required, which is apparently not much at all. This, plus my experiences in researching transportation efficiency (possibly a topic for another blog!) led me to understand the we have created a lot of the "built" world around us with little consideration of using energy efficiently. Another way of saying this is that we have embedded the assumption of incredibly cheap and plentiful energy into nearly everything we have built. To me, as this embedded assumption becomes less and less true, as it already has and as I predict it will over the next decades, more and more rapid disruptions will be forced upon us as our infrastructure becomes infeasible. I noticed a good bit of this during the oil price shocks of the last couple of years, and oil prices only affect the transportation part of the energy picture. I think it's self-evident that the hardships will be even more severe when the price of non-transportation energy, i.e. electricity, undergoes significant increase.
So how can we protect ourselves against the already noticeable increases in the cost and scarcity of energy? One way, friends, is energy efficiency in all things! There is a cost (monetary, environmental, and in land use) with any form of energy generation. It seems clear that the best thing we can do to help all of the above costs is to use the energy we generate as efficiently as possible, something we are patently not doing right now on a broad scale in this country.
The preceding paragraphs begin to touch on the second reason, a wide and oddly controversial topic called "environmentalism", which I won't explore in detail on this blog, in part because there are many great sources of information about it, including this blog that specifically touches on current environmental issues in America. While I like to think of myself as somewhat environmentally aware, my energy use alone probably disqualifies me from any great pretense of being "green". First and foremost, I live in a single-family home, the most energy inefficient way humans to protect themselves from the weather, and the creation of millions of which have forced the expansion of cities outwards far faster than if people lived more densely, causing billions more miles of vehicle trips every year. Second, I live in a city with poor mass transit options, death-defying bike lanes and/or lack thereof, so I drive a 2200 pound monster that spews CO2, NOx, and VOCs into the air anytime I have to get somewhere. Granted, I chose the cleanest, most efficient monster I could find, but that doesn't magically eliminate the fact that I'm burning the energy to take 2200 pounds for a ride every time I go somewhere; it just reduces its impact somewhat. Finally, at this point, my already energy-inefficient house (due to it having 4 walls and a roof leaking heat just to protect a very few occupants) is even more inefficient because it was built with minimal (if that) consideration for energy, and I'm not done retrofitting it yet :)
But fear not, adventurous reader. After a brief diversion into other energy-related matters, more improvements are afoot.

Worth it...financially?

2009-09-20T19:32:00.000-07:00

In my last post, I described some reasons why doing the work I'd done through 2007 was worth it. But I am aware that many readers want to know how different efficiency measures pay off from a purely financial point of view. This is certainly a reasonable question, although I would disagree that it is the only meaningful arena of consideration.
But to help answer the financial question, I will consider my first three improvements as a unit, since I performed them in a roughly overlapping span of time. Here are the numbers, as best my records have them:
Data:
Approximate capital cost of improvements: $1150.00
Approximate average reduction in monthly bills: $50.00

Calculations:
Payoff time: $1150 / ($50/month) = 23 months = about 2 years
Effective interest rate: (100% / 2) = about 50%

For comparison, the effective interest rate for a good bank account is maybe 6% these days. So, interested readers, peruse the following statement and marvel: my investment in energy efficiency is earning me over 8 times the effective rate of a savings or bank account.

One caveat in this is that I have discounted my own labor rate. For 2 of my 3 improvements, I paid for someone else's labor, so the calculation is correct. For the other improvement, I used my own (unpaid) labor to remove the old insulation blocking my soffits. This labor cost should ideally be included, which would reduce my effective interest rate. However, I did not track my hours of time on this. I would highly doubt that it would lower my interest rate to anywhere near the going bank rate.

One lesson from all this is that if you do these improvements yourself (i.e. you have more time than you do money to spend on energy efficiency), then you can reap incredible financial returns on your investment. In my case, over 50% of the money I spent was on paying for someone else's labor, not on materials. Had I done this work myself, spending more quality time in the attic, I would have more than doubled my effective interest rate, paying off the materials used (a ridge vent and baffles) in a single year.

One thing a lot of folks seem to assume is that after the payoff period (about 2 years for me), the improvements are "done" - that is, they are no longer making you money. This is the exact opposite of the truth. Every single month, from here until I sell my home, my investments in energy efficiency will keep my bank account $50.00 higher, which is the same as if I had a nice fat checking account sending me that amount in interest. In fact, these improvements give me the added benefit of "energy price insurance": should the cost of energy continue to rise, as it has in the recent past, the value of my investment goes up. My $50/month savings will be come $100/month savings if the cost of energy doubles.

So, according to my calculations, if you have any money to invest, investing it in your own energy efficiency makes a incredible amount of sense. "Should I put that $1000 in a savings account at 6% or into my attic at 50%?" For most of us, this question answers itself.

And not to put too fine a point on it, but I've still got another 2 years of improvements to tell you about. Be patient, energy efficiency enthusiasts, and read on!

Taking Stock: The Bottom Line

2009-09-07T13:43:00.000-07:00

It was now the spring of 2007. I had successfully navigated the early waters of what amounted to the early low-hanging fruit of energy efficiency in my house:

1) Ductwork leaking conditioned air into the attic
2) Soffit vents blocked for many years by insulation
3) Insufficient and badly placed attic vents

Our electric utility company keeps online records of customers' electric usage by month. Using their numbers, I have been able to quantify my electric usage changes. Note that this is not a perfect analysis; for example, it does not take into account the fact that one summer does not have the exact same weather as the next. A fair disclaimer: the summer of 2007 was a cooler and cloudier one than 2006, the last summer before I made the improvements. Actually, the improvements started in 2006, so I will compare to 2005 readings. Nevertheless, the only data I have to compare are the utility readings, so here are the numbers:
Electric usage in 2005: 14,000 kWH
Electric usage in 2007: 8,000 kWH

In other words, the improvements had yielded at most a 44% improvement in my yearlong energy use, as best I can measure. The number may be somewhat less due to the unusually "cool" summer of 2007.

In addition to improving my energy efficiency quantified above, these few improvements had the following benefits:
A) Healthier air in the house. The leaky ductwork not only allowed inside air into the attic. By connecting the two airspaces, it must also have allowed attic air into the house. Attic air is chock full of dust, fiberglass fibers, mold spores (largely present due to #2 above) - this is why we wear masks when we work up there. Sealing those ducts has made the residents of the house healthier.
B) An attic less conducive to mold growth. The moldiest areas of the attic that I found were at the back of the house, where the soffit vents had been blocked since the house's construction. Increased airflow will keep moisture from being trapped and condensing in the attic, which will greatly slow the growth of mold.
C) The garage is noticeably cooler when I leave in the morning, and return in the afternoon. This just makes it a less unpleasant place to be when I have to be in there.

So was it worth it? I would have to say that I would not be Energy Efficiency Man if I felt that it were not. Although I started these projects from a standpoint of energy efficiency, as I learned more about the other benefits of my efforts, I becamse excited about them as well. Is there anything wrong with wanting to breathe air that isn't shared with fiberglass insulation? Is there something wrong with wanting to not reside under the world's largest urban mold colony, or not wanting to break a sweat when walking 8 feet to your car in the garage? No, indeed, gentle reader, but for the present, we will return to Energy Efficiency. (We will explore financial worthwhility in the next post).

For as great as progress was in 2007, I had whet my teeth on the gristly but chewable edge of making a single family dwelling energy efficient, and still I hungered. I had stuck my toes into the cool waters of a new way of thinking, and in my Web travels seen the obscure edges of such exotic concepts as reflective radiant barriers and R-values of materials. I longed to experiment with these concepts, with their efficient and (near and dear to my heart) low maintenance possibilities.

So follow me, gentle Reader, as I proceed into the next level of Energy Efficiency, for we have yet a ways to travel, more to learn, and Energy Efficiency to gain.

But was it too much?

2009-09-07T13:19:00.000-07:00

In the last episode, we attacked the second part of our attic airflow problem by installing a ridge vent to let the hottest air out of the top of the attic. So now I had a fairly complete intake system of open soffit vents and extra grille vents, as well as a real outflow system. But, as the careful reader will recall, the "net free area", or airflow capability, of the intake and outflow systems should match as closely as possible.
The ridge vent manufacturer helpfully supplied the net free area per linear foot of vent, and given that I knew the length of my ridge, I could calculate my total outflow. In addition to the ridge vent, I retained the two original "turtle vents" (holes with an inverted pan over them to keep the rain off), since they still seemed to operate properly - which we checked with a simple piece of paper held below the vent on a hot day - the paper was sucked up against the turtle vent, showing that the airflow was still out. This mattered - if I had changed the dynamics of the attic too much, the turtle vents might have become intakes, bringing very hot air off the shingle surface into the attic: definitely an Energy Inefficient situation.
So, by adding up the ridge vent area and estimating the turtle vent area, I got a rough number of the net free area of my outflow system. The hope was that my inflow system would roughly match, or slightly exceed (according to some sources) that number.
I didn't have specifications for my soffit vents, but some back-of-the-envelope estimates multiplied by the measured length of the perimeter of my house yielded a good estimate. I added to that the net free area of the grille vents I had added. The result: I still was short of intakes, by a pretty good amount.
In the meantime, I had noticed another possible Efficiency Issue with the house: the garage in the summertime tended to get very hot during the day, and tended to hold that hot air, right against the house, for the entire night. In most people's books, holding a large reservoir of hot air against a surface who's other side is being cooled is a no-no for efficiency. In fact, this problem yielded another chance to kill two birds with one stone.
How to cool the garage and add more intake area to the attic at the same time? Well, as good luck would have it, my attic access hatch was located in the garage. This was cause for another Eureka moment: I could leave the attic access hatch slightly open, leave the garage door open slightly to allow air in (but not so open as to allow the neighbors curious cats in), and voila! The outside air would flow into the garage all night long, up the attic access, through the attic, and out through the ridge vent. Instant no-moving-parts, no-electricity-required cooling for the garage and supplying of air for the attic. As readers of this blog might well imagine, words alone cannot express the excitement I felt when I realized this commonsense answer to my dilemmas.

Problem: Inflow area into the attic insufficient to match ridge vent
Problem: Garage holds heat all summer long
Solution: Slightly open garage door, slightly open attic access in garage, instant cooling!
Lesson: I don't always have to buy or install something to solve an Energy Efficiency issue

Ridge Vent to the Rescue!

2009-09-07T12:45:00.000-07:00

Problem: Not enough outflow area for hot air to leave the attic
Problem: Existing outflow vents on the roof are not even near the peak

Searching the web for solutions to these problems yielded a growing consensus: the best way to ventilate a modern attic is a combination of soffit vents for air intake into the attic, which I had recently cleared, and something called a ridge vent for outflow of the hottest air from the attic. The ridge vent is nothing more than a couple of long but narrow slits cut through the roof beside the longest peak at the top of the roof. For my house, the longest peak doesn't run the full length of the house, but it does run about 2/3 of the length. The ridge vent also includes a covering made by a ridge vent supplier that gets installed over the top of the slits so that rain does not fall right into the attic. There is some art and value added by the different vendors in this component - different designs allow better or worse airflow, are better or worse with wind-driven rain, etc.
The thing that Energy Efficiency Man likes about ridge vents is that they are simple, have no moving parts to wear out, and will require very little maintenance. For some ridge vent systems, there is a filter over the slits that will require changing every few years, but that is about the extent of ongoing maintenance. Finally, in my particular case, the fact that this solution is placed at the peak of the roof means that it solves both of my problems in one fell swoop.
Before we proceed to my particular experience with ridge vents, I should note that there are some vocal detractors of the technology out there. I have seen claims (mostly from one person who sells a competing system) that ridge vents won't work well because the covering forces hot air to flow down momentarily, which it doesn't want to do, to work its way out of the attic. While this is true, I would challenge folks to design a roof vent that doesn't require something like this and still blocks rain from entering the attic. Most existing vents have this problem. Furthermore, and this is yet another area where aspiring Efficiency Men and Women out there should consider their own local weather patterns, my area has pretty consistent winds through the summer months, and in my case, those winds flow across the roof perpendicular to the wind. Due to the Bernoulli effect that we all know and love, that familiar physics principle that makes sailboats move and airplanes fly, the prevailing summer winds create a low pressure area on the downwind side of my ridge, and a higher pressure area on the upwind side, creating a "pump" that helps move the air out even faster than hot-air convection normally would. At least this is true in theory; I have no easy means to test it.
But back to my own experience. In short: I decided on the ridge vent, and I had the good fortune to find a workman who would buy and install a ridge vent for me for a very good price. In one afternoon he had cut the requisite long strips out of the roof, and unrolled and installed the ridge vent rain baffle/air filtration system over the long cuts.
However, one question remained foremost on my mind: would the new outflow area be enough to balance the intakes? The answer to that question will have to wait...

Solution: Ridge vent installed at the very top of the roof

Up, up, and away!

2009-08-27T20:47:00.000-07:00

Before I proceed to talk about air outflow, a small diversion into the theory of operation of a modern ventilated attic might be in order. Most of us are taught at a very early age that hot air rises. In fact, this basic principle is the foundation for the entire self-ventilating attic concept, an idea elegant in its simplicity yet apparently surprisingly hard to come by in the real world.
The idea is that the attic will naturally heat up during the day, from radiated heat from the sun hitting the roof as well as convected heat from the house below (cooking, lights, computers, hot showers, etc.) If this heat is given a vent to flow out of, and if there is a suitable vent for cooler air to flow in from, the basic principle of hot air rising will force the hot air out, and the cool air will be naturally drawn in by the reduced air pressure (the suction left behind, if you will). The elegance of this temperature-difference-driven cooling engine is exhibited by the fact that it has no moving parts to wear out and that it uses no electricity. In short, a properly ventilated attic puts the laws of physics to work for you!
So, back to my particular attic. Having satisfied the rule of thumb for the amount of air intake for my size attic, I needed to make sure that my air outflow was properly accounted for. As it turns out, the two small square vents that I had were a good bit short of the net free area that I needed. The net free area is a measure that can be found on all ventilation devices, and it is less than the actual measured area of the device since all of them have some sort of covering, grill, or mesh that impedes airflow. In addition, my vents were a good 30% below the ridgeline of the roof. In other words, the top 30% of my attic airspace would heat up all day, and never leave the house. This, once I thought about it, was intolerable. I was keeping the hottest portion of the air in, while venting the cooler portion out! I might as well have stood there all night, tearing up dollar bills, because that is effectively what my house was doing via my energy bills.
In short, dear readers, the situation with my attic outflow was intolerable. How could I best get more outflow area? How could I get it located higher up on the roof? I returned to my computer and began more web research...

Intake Inspiration

2009-08-03T20:15:00.000-07:00

Ah, many are the Americans who have pondered the means by which to allow more air into their attics. Energy efficiency has called, and we have proudly answered!
Despite my ongoing troubles opening enough channels for the soffit vents to flow through, I realized that the design of my house allowed me one more way to get air into the attic. My back porch is basically a cut-out corner of the rectangle of my foundation, if you will, but over the porch there is some roof (see photo above). The bottom of that roof was unventilated but that could be fixed... but did it connect to the attic airspace?
Imagine my triumph as I realized that it did when I spotted the top of my porch light from the recesses of the attic. Imagine, if you even can, my further triumph when I realized that this porch was right in the middle of the longest run of unventilated vaulted ceilings.
Although the area is mostly inaccessible from the attic, I was able to cut out holes for some grill vents from below with the help of a drill to get started, and a handy tool called a keyhole saw, borrowed from my helpful neighbor. Although I got a face full of insulation for my trouble (why they insulated over the porch I don't know), I was able to place two grill vents each of which carried more air than several baffles. In short, it was no less than a full-on ventilation coup.
Here is a picture of the grill vents from below.

Now, although my intake problem was not fully solved, it was as good as it was likely to get for a while. With that, I turned my attention to the complementary problem: outflow of hot air.

Moldy Mission Creep

2009-08-01T23:52:00.000-07:00

My goal: open up the blocked channels to allow airflow. The channels were each defined by two ends, one in the attic and one at the soffit vents leading outside, and 4 sides: the roof on top, the sheetrock of the ceiling on the bottom, and two wooden rafters. They were completely filled with insulation.
My plan: Clear the channel, slide in a baffle along the top, staple the baffle in place against the roof, then slide the insulation back in place. The difference: with the baffle in place pressing down on the insulation, the air could flow in through the soffit vents then pass above the insulation and into the attic.
Note: A baffle is an inexpensive piece of plastic or styrofoam that is shaped to create an airspace. Mine look something like 4 foot long rectangles with 2" edges sticking down along the sides, but open at the ends to allow the air to flow through.
Here's a cross-section looking down the long (open) axis of a baffle that I've added radiant barrier to (more on that project that later). It's about 4 ft x 2ft x 2 inches.

Of course, opening up the blocked channels leading from the attic down the slope to the soffit vents a good 8 feet away entailed removing the insulation. At this step, I noticed that a lot of the insulation that I was removing was infested with a good amount of dark colored junk, almost certainly mold. I live in a humid climate, and mold is certainly not unusual. However, recalling that discretion was sometimes the better part of valor, and I decided to replace the insulation with new stuff. Much of my reading on attics detailed how improper ventilation creates good conditions for mold growth.
I was now entering the phase that many of you engineers out there may recognize: mission creep (or for you software folks, feature creep). That is, the point at which you start to decide that some new activity that touches on your original activity really should get done.
In this case, the mission creep added new steps for each channel to be cleared. Each channel now required:

Surveying the channel to see if there was room for my body in front of it
Clearing space from the blow-in insulation for my movable flooring
Putting in movable flooring to work off of
Reaching far down the channel for the old insulation (with my handy-dandy broom handles to assist in compression and grabbing; otherwise the insulation would just tear and not move)
Removing (and plastic bagging for safety) the old insulation
Creating a double-length-baffle (the store baffles were too short; I had to staple two overlapping to get the length and strength required to put them down the channel).
Sliding and stapling the baffle in place against the underside of the roof.
Unrolling, measuring, and cutting new insulation
Stuffing the new insulation down the channel (involving the broom handles and creative vocabulary as the insulation snagged on roofing stapes, large splinters, and stray pieces of plywood lining the channel)
Removing the temporary flooring
Restoring the blow-in insulation underneath me as best I could

I performed this 11-step dance for a number of work sessions in the attic, often getting only a single channel done due to the difficulty of doing _anything_ useful in the tight space. After a time, I had completed about 8 channels. There was a nice reward on each channel, verifying for me that my plan was working even in the early spring weather: as I removed the old insulation on every single channel, I felt a tangible breeze of fresh outside air blowing into my face, feeling almost like it had been waiting patiently for years trying to get in and save me some energy. After sweating and maneuvering for many minutes, this small reward was a blessing.*
Now I had cleared all the channels that I could physically get to in the attic. It still wasn't enough, but it was a help.

* Again, Efficiency Man recommends that you hire a trained professional for extensive attic work, for reasons of comfort and safety. If you must do the work yourself, protect your lungs with a mask rated for insulation, and your skin with a good covering.

Next: A ray of intake inspiration

The Tip of the Intake Iceberg

2009-08-01T16:12:00.000-07:00

After a winter of reading and plotting, I decided it was likely that I indeed did not have enough ventilation in my attic. The various guidelines (such as this), most of which seem to be rules of thumb, seem to show that I'd need about 6-7 square feet of ventilation, evenly split between inflow to the attic and outflow from the attic for my 2000 square foot house. Some folks debating the topic state that I need double that, which is entirely possible particularly in my hot central Texas climate. What I had existing was approximately 1.5 square feet of ventilation in the roof, and that, not even close to the top where the hottest air would gather.
The villain begins to become unmasked.
My home was marketed to me as fairly energy-efficient, and I do believe that for mid-1990's standard, it was not designed too badly. In fact, the continuous soffit venting around the eaves was a good feature for capturing breeze into the attic from any direction. However, design is only part of the equation: installation is another thing entirely. Looking around in the attic, I noticed a new problem: nearly half of my soffit venting was blocked by improperly installed insulation. This, added to my decidedly under-vented roof, revealed more of my problems.
The reason for the blocked ventilation was soon revealed: roughly half the house has vaulted ceilings (also called cathedral ceilings). These are the areas where the ceiling, when viewed from inside the house, slopes downward to the walls, rather than being flat all the way across. When viewed from above in the attic, the slope starts at the attic floor and goes downwards towards the outside wall. The problem is that the roof is only about a foot above this slope, creating a foot-tall channel that can be easily blocked by insulation batts (the rectangular pre-cut pieces of insulation).
Problem: Seemingly insufficient soffit air intake to the attic
Cause: Nearly half the inflow (soffit) vents are blocked
Solution:
Air could not flow out the top of my attic if replacement air could not flow in from the bottom. So, in the first real preview of the Efficiency Man spirit, I decided to start crawling around in the attic and opening up blocked channels where I could.
Note: Doing this yourself is not for the faint of heart, short of breath, poor of balance, or lacking of insurance. Working in the awkward spaces, often without proper flooring, while wearing a hat, disposable paper suit, mask and gloves to protect from the insulation fibers, makes just moving around up there difficult. Add to this the poor lighting and the dust you inevitably stir up, and you quickly realize that working in attics is tough on your health, and, as a bonus, hazardous - there are nails poking out in many places, ducting to trip over, and wiring to avoid. Although you should practice the Efficiency Way whenever you can, know your limits and hire a professional for extensive attic work. I personally want to avoid the attic for a good while after this.

Water Heater Part 2: The mystery deepens

2009-08-01T10:09:00.000-07:00

The recalcitrant gas hot water heater in the attic still had more to teach me. It continued to periodically extinguish itself. As the summer of 2006 went on, I got tired of going up every few weeks to relight the pilot light. I called a plumber, who, streaming sweat from being in my sauna-like attic, complained that the attic was too "tight". Having recently learned insider terms like "tight", I knew what he meant. Was it possible that there was not enough airflow through my attic? Why should there be airflow through the attic at all? There were, in fact, two small attic "turtle vents" just above the hot water heater, although their placement on the roof roughly 30% below the peak seemed counterintuitive even to the not-yet-Efficiency-Man me of 2006. And finally, was it conceivable that lack of airflow was so bad that it was choking my pilot light due to lack of oxygen?
Intrigued, I began to Google and read up on what I found.
What I discovered, dear readers, has formed the main portion of my energy-inefficiency-fighting career to this point. The biggest opportunities for energy efficiency in your home, and for fighting the triple behemoths of Energy Inefficiency, Large Utility Bills, and Not So Comfortable Home, can be found right upstairs in the attic.*
Incident: Continually failing pilot light
Problem: Seemingly insufficient airflow
Solution: Stay tuned...

* This is true in my neck of the woods, central Texas. From what I have read, the attic is the main efficiency issue in many climates, but you should research your own area. Solutions that are appropriate for Efficiency Man may be less appropriate for readers in other areas.

The Beginning: A Lucky Break

2009-08-01T09:35:00.000-07:00

It all started back in late spring 2006, when I was in the attic, relighting our natural gas hot water heater for the third time that year. By lucky coincidence, the air conditioning blower unit came on right behind me as I sat in front of the water heater. I felt cool air blowing on the back of my neck, right there in the attic. Even as uneducated as I was at that time in the Ways of Efficiency, I knew that this implied a large waste of resources. Leakage in the air system meant that I was expending energy and money trying to cool the attic, which is connected to the outside world. You can't cool the outside world with an air conditioner no matter how much energy you burn. Note for civilians (non engineers): air conditioners do not cool overall, they simply expend energy to move heat from place to place, typically from inside a space to outside it.

Incident: Conditioned air leak detected in attic
Problem: Normal duct aging
Lesson: After 10 years or so, it is expected that air ducts will be leaky in any building, leaking up to 30% of their air conditioning energy in a futile effort to cool the outside world.
Solution: Do it yourself (Google "duct sealing diy" and do some reading) or pay someone to fix it. At the time I paid a local well-known plumbing contractor to perform a full house leakage test. The crew of two men spent an entire day sealing not only the attic ducts, but looking at every airspace penetration (doors, windows, plumbing that goes through the wall) and sealing it. At the end of the day they performed a fascinating test to prove the system was sufficiently airtight (or "tight" in their term): they covered every air register with plastic, and attempted to use a fan to suck air out of the system from the return air vent. The harder the fan worked, the more tight the system. The system was tight. They then sealed off the main house airspace from the duct work, and replaced my front door with a "blower door", which again had a large fan that attempted to blow air out of the (sealed) house. The harder that fan worked, the tighter the seal of the house. The house was tight; the air duct system was tight; the problem was solved.
Moral: Leaky ducts throw away energy and money. Energy efficiency waits for no man! You know what to do.

Introduction

2009-08-01T09:18:00.000-07:00

Welcome to my blog! I am EnergyEfficiencyMan. I became interested in energy efficiency about 5 years ago, probably for the dual reasons of an engineering background and years of utility-bill-laden home ownership. In addition, I read a lot, both on the web and in periodicals. Much of what I have seen and experienced firsthand has made me realize that our society, in particular modern American society, has the following characteristics:

We have built a world which requires large amounts of incredibly cheap energy to maintain
We waste between half and 3/4 of the energy we generate without putting it to good use

With these two reasons, an alter ego and a mission have been formed. Investigate on, intrepid readers, for enthralling information about a man, his slowly-improving-in-efficiency single family dwelling, and a quest that continues to this day!

Executive Summary

For those who don't want to traipse through my entire blog, I'll summarize some of my key findings here along with links to the more detailed entries.

In 2005 -2006 I got my ducts and house sealed for air leaks and improved my attic ventilation. Reduced energy usage by 40% from my 2005 value.
In 2007-2009 I installed radiant barrier over almost the entire attic. Energy usage was now reduced by about 60% of my 2005 value.
Along the way, I learned a lot about energy in human terms, attics, ridge vents, the three heat flow mechanisms, radiant barriers, and modeling to account for weather variations.