Image Credit: Mark Teskey
More Musings of an Energy Nerd
Electric resistance heating systems have a bad reputation. While the required equipment is cheap (and sometimes cheap-looking), homes with electric heat are known for their high fuel bills.
Yet some residential designers are beginning to rethink the old prejudice against electric resistance heating systems. After all, if a house has a very tight, very well insulated envelope, the heating load can be quite low, and so can the utility bills — even when using an expensive fuel like electricity. Moreover, all-electric homes don’t need a chimney, avoid minimum utility charges for natural gas, and don’t have any worries about fuel storage, fuel fumes, or backdrafting. Electric resistance heaters have much fewer maintenance issues than appliances that burn gas or oil.
Finally, if the homeowners ever want to install solar panels on their roof, the electricity usage in an all-electric home can eventually be balanced by a photovoltaic array.
Integrated design works well
An excellent example of an energy-efficient all-electric house is one designed by Rachel Wagner (of Wagner Zaun Architecture) for Gail Olson and Erik Peterson in Esko, Minnesota. Gail Olson is the fourth generation of her family to live on the 65-acre farm where the new farmhouse was built. The home was completed in 2009.
Using an integrated design approach, Wagner pulled together a team that included the homeowners, builder Steve Johnson, and energy consultant Michael LeBeau (of Conservation Technologies). Wagner recalls, “I’m proud of how well the integrated design process went, from the site assessment, to interviewing the clients and understanding their needs, wants, and goals, to weaving it all together. It yielded a result that is pleasing and functional and really durable.”
The owners are delighted with their house. Olson said, “I feel incredibly lucky to have a designer and builder who work on low-energy houses…
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24 Comments
Super House!
The performance numbers for this house are fabulous, about .75 Btu's per sf per Hdd. The dark and cold months of December, January and February make up the majority of the heating usage in a superinsulated home in a cold climate. For comparison puposes, new MN code built homes average about 3.5 Btu/sf/hdd.
The solar contribution is larger than one might think for a superinsulated home. I found it to decrease my Btu/sf/hdd from around 1.35 for a house with little or no south facing glass to .9 for a house with good solar orientation. High solar gain glass probably would have improved the best house performance.
The electric heat portion of
The electric heat portion of the electric bill is indeed quite low, yet Wagner seems to express concern about use of electric heat being higher than anticipated. What the numbers don't show is what that part of the electric bill might have been without the woodstove. In a house like that, even a small woodstove will heat the house all by itself when in use (except for the basement).
Despite the owner saying: “My sense is that the air-source heat pumps aren’t efficient in our climate,” the COP of any air source heat pump always will be greater than 1. While the COP will fall off considerably as the outside temperature falls, the power use still will be leveraged substantially. It just seems to be a waste of power not to use it to drag some outside heat in with it.
I'm curious also about the apparent lack of an outside air kit (OAK) for the woodstove. True, a small woodstove draws perhaps just 40-50 cfm of air, that's still more than the natural leakage of a house that tight. While the draft through the chimney pipe will keep the stove drawing properly, the flow likely will put the HRV into imbalance to make up the difference, and that imbalance results in lower efficiency of the HRV.. I'd be interested in hearing why no OAK was used.
Calculating BTU/sqft/HDD
I ran some numbers for the house, to see perhaps how Doug ran his. For area I used 3150 (1950+1200) sqft. For heating degree days I used 9818 (http://www.clrsearch.com/Esko_Demographics/MN/Weather-Forecast-Temperature-Precipitation). For heat load, I used the table numbers (3777 kwh) plus the 1.5 cords of Aspen at 14.7 million BTU/cord 70% efficiency (http://www.hearth.com/econtent/index.php/articles/heating_value_wood). So my math goes:
(3777 * 3412 + 1.5 * 14.7E6 * 0.7)/(3150 * 9818) = 0.92 BTU/sqft/HDD, The woodstove is providing 54% of the total. Using the first year's electric heat use (3276 kwh), the total heat load comes to 0.86 BTU/sqft/HDD, with the woodstove providing 58% of the total (numbers assume same HDD and wood use).
Response to Dick Russell
Dick,
Thanks for doing the math -- very useful calculations.
Nice job, people.
‘Better building, less technology’ - now there's a concept. Can't believe how small and simple that boiler is.
Calculations
Dick,
You read the information better than I did, I used 1/2 cord per year instead of 1 1/2. Hdd for Duluth, MN is 9,742 but that is 1970 to 2000 average, probably 300 or so less these days. A more accurate calculation would take the actual hdd for the period monitored, I guessed 8,500 average for the 2 years. My recalculation puts this house around 1 Btu/sf'/hdd using 70% wood burning efficiency. Aspen is a poor firewood and unless it is properly seasoned the Btu per cord could be a fair bit less than 14.7 million.
hdd for Duluth
Acoording to the Weather Underground the hdd for Duluth, MN for the period 5-3-09 to 5-4-10 is 8,715 and for 5-4-10 to 5-3-11 is 9,381. Average for the 2 monitored years is 9,048 hdd, average energy used for heating is 27,467,418 using Dick's wood heat calcs. My third and final attempt, .9737 Btu/sf/hdd.
This is a very efficient house, the .40 ACH50 is impressive. Would like to know about the mechanical ventilation rate and the HRV efficiency for further analysis. We sometimes overventilate very airtight homes and heating the ventilation air becomes a major portion of the heating load. Knowing Rachel and Mike, they did not scrimp on ventilation and I am all for being safe.
Will the real HDD please stand up.
After posting, I googled for sources of HDD information. One site showed HDD for me (central NH) at over 14,000, high by a factor of almost 2! Even for Esko MN I saw a lot of variation. What's the "gold standard" for HDD data?
Cloquet vs Duluth hdd
If I put Esko, MN in the Weather Underground search, Cloquet comes up. Cloquet is probably closer to Esko and a more accurate hdd reference. For the period 5-3-09 to 5-4-10 the hdd is 9,215 and for 5-4-10 to 5-3-11 hdd is 9,435. This puts the Btu/sf/hdd for the house at .935
Duluth is right on Lake Superior, there is lake effect and also a bit of heat island in the city of Duluth I would think.
NH 14,000 hdd
Dick,
The 14,000 hdd in NH is Mount Washington, 6,288 ft, a very cold place. Superinsulation would be a good choice there.
Nice write up. Thanks to
Nice write up. Thanks to everyone involved for sharing some of the details and costs. Hadn't heard of Duxton windows. Also surprised how tight the house tested using poly as the air sealing layer.
Curious whether in theory an HRV (or a bypass in the system) could be rigged to provide additional combustion supply air while a wood stove is being fired.
And why such a big hot water tank? Future solar thermal planned or does it assist the electric boiler?
Response to J Chesnut
Jm,
Q. "Why such a big hot water tank? Future solar thermal planned or does it assist the electric boiler?"
A. No, it doesn't assist the electric boiler. Your first guess was correct.
Wood heat
As I look again at the specifications for this house I believe the wood heat contribution has been overestimated. I have experience monitoring similar homes in a like climate and I see so many thermal improvements on the Esko house to the double wall homes I built. The foundation is very well insulated, the windows are far superior, the ACH 50 is about 1/3 of my test readings. The HRV is likely far more efficient with much better control than was available in the 1980's. The design is very clean with a favorable surface to volume ratio.
It would be interesting to forgo the wood heat for a monthly electrical billing period to see the actual heating load. This is just a fine looking house and a great achievement for all involved. I applaud the owners for using the wood resource to lower fossil fuel usage.
On calculating percentages
Whenever someone calculates that (for example) "the wood stove is providing 54% of the space heat," one needs to ask the question: what else is under consideration?
Are you including internal loads? If so, what is the percentage contribution of internal loads?
Are you including solar gain through the windows? If so, what is the percentage contribution of the solar gain?
Base usage
The summer electrical usage provides the data for the non-heating portion of the electrical bill. From this summer monthly usage an internal gain of sorts could be estimated. Internal gains are not what they used to be with cfl's and higher efficiency appliances, unfortunately this is often offset with a house full of electrical gadgets.
The Esko house is efficient, not quite PH, but very close.
House contruction and elec. heat
I'm in the process of designing an addtion to my summer home, whiich will become a permanent residence in the future.
I am alined with the thoughts about const. with the above house, but have a few ides that are different.
1) I would use insulated panels on the outside rather then using double wall const.
2) In place of the electric system, electric radiant floor heating would be my choice.
3) To me, make-up outside air for thr stove would be mandatory.
4) PV panels will be incorporated on the gargae roof.
Comments?
Why cellulose?
After looking at the photos and reviewing the article it seems using a loose fill insulation proved a little tricky in some parts of the structure? What was the reasoning for going with a loose fill, like cellulose and not a polyurethane spray foam?
Response to Patrick
Patrick,
The list of reasons is long... But I'll start with cost, embodied energy, and environmental impact.
Deceptive Headline
Martin,
The headline and opening discussion suggests, shockingly, that you are about to build a case for electrical resistance heating as a primary source option. I read the article thinking you had completely lost your marbles this time and was even more shocked to find out that this was one of Rachel's homes. That was when I knew something was up.
There is no one in the green building movement in MN who advocates for, or would ever advocate for, the use of electric resistance heating as a solution UNLESS it was off the grid and using an alternative electricity generation method. The region's primary electricity generation comes from coal and the mercury contamination of lakes/streams/fish in MN is absurdly high. Folks are advised not to eat more than a couple lake caught fish a month because the levels are so high. (But that is an environmental issue and not something you are fond of discussing)
It looks to me like Wagner was advocating for her wood burning stove (which I find absurd for a different set of reasons) as the primary and her resistance boiler as a second. It would appear you also struggled with the burning of wood in a stove as an option here, but I see nothing in the design of the house, the architect's intent (misguided or otherwise), or the results that suggests for a one second that Electrical Resistance Heating is an option that should be considered.
In fact, Martin, it would appear that this home makes a case for propane.
Michael
Response to Michael Anschel
Michael,
In the article on this page, I think I accurately reported the decision process that led the homeowners and architect to choose electric resistance heat for this house. This case study reports on a project; it is not an advocacy piece.
Obviously, homeowners, builders, and architects make decisions like this all the time, and any reader is free to come to a different conclusion. I'm reporting on one story, and on the decision of one particular design team.
As I pointed out, one of the advantages of an all-electric house is the opportunity to balance the home's electrical use with a photovoltaic array. Many people all over the country are choosing to do this; as I reported in the article above, Gail Olson and Erik Peterson have not yet purchased a PV array, but they could.
Anyone who feels strongly that propane is a more appropriate fuel than electricity should call up their local propane dealer and ignore the example of the house described here.
Response to Dick Russell about OAK for wood stove
Dick, Better late than never, I hope. We struggled with the question of whether or not to install a dedicated combustion air route for the wood stove. In the end, the builder, performance consultant, and I all agreed that the home would have enough combustion air for the wood stove (and it does). I don't think it is possible to put the HRV/mechanical ventilation system "into imbalance" because it the system is, by definition, a balanced ventilation system. The amount of air supplied and the amount of air returned remained pretty much equal in this closed system. Now, because it is so tight, the house can go under negative pressure when the dryer or kitchen exhaust fan runs, since each of those appliances exhausts about 150 cfm. And this is where the woodstove can be problematic, since the stove and chimney might be the easiest route for make-up air to be claimed. And so this is why we suggest our homeowners to crack a window in a super-tight house with a wood stove and another exhaust-only appliance. But, as I understand it, the combustion air intake for the wood stove would not have solved the problem of the wood stove-make-up air conflict in a tight house. Hope this helps.
windows
After reading the blog about high-end windows being a waste of money, how do you think cheaper windows would affect the performance of this house, and how much $ would they save?
Response to Steve Hansen
Steve,
Good question. To find the answer, the designer needs to use energy modeling software to model the house two ways (with two types of windows under consideration).
Then it's up to the clients to decide what they want -- and whether the annual energy savings of X dollars justify the additional investment of Y dollars.
My own opinion: in a cold climate, triple glazing is a good investment for comfort reasons alone.
I think that the real debate concerns whether expensive Passivhaus-certified windows from Germany can be justified; such windows cost much more than the Duxton windows from Canada used on this house.
Any idea on a price range for materials to build a house similar to this one?
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