Friday, October 15, 2010

Expecting the unexpected

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.

Thursday, September 16, 2010

Fun with the Passivhaus

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:
  1. 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.
  2. 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.

Wednesday, September 15, 2010

Moderate efficiency, radical conservation!

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:
  1. How far is it from point A to point B, and what mode of transport is appropriate for this distance?
  2. 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!

Monday, August 30, 2010

What is that radiant barrier thing?

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!

Wednesday, August 18, 2010

The Key Principle of Energy Efficiency

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:
  1. The up-front cost and effective interest rate of the improvement
  2. The environmental impact of the improvement
  3. 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!

Monday, August 9, 2010

Reflections midway through the summer

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!

Monday, March 15, 2010

A Long Awaited Analysis

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:
  1. 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.
  2. 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.
  3. 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.
  1. 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.
  2. 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.
  3. 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!