December 21st, 2010

Second Blower Door Test

This morning we had our second blower door test done… Its not normal to have to get a second test done, but our house doesn’t fit very neatly into the LEED so after being granted a series of appeals, we are getting new performance tests.

Size and Efficiency

Throughout this process, there are two scoring systems that have been used to rate the efficiency of our hosue, HERS (used by ecostar and LEED) and EPS (used by energy trust). We recently received a nice bit of incentive money from energy trust due to our EPS score (26), however our score with HERS shows us as a basically average house. The reason for this is the method of calculation, EPS is based off of direct usage, the 26 we scored is 26MBTU of total energy used throughout the course of a year… HERS, on the other hand, compares the energy usage of your house vs a reference house, and in that comparison is a size adjustment, effectively ranking your house on a square foot basis. Our house for instance is about 2/3 the size of their one bedroom reference home, so our usage is scaled up by 150% through the size adjustment. The problem stems from the fact that the largest energy users in our house are not scalable things like heat loss and lighting, but are appliances that every house will have one of such as a hot water heater, refrigerator, and oven. So in effect, our kitchen and bathroom (the majority of our energy use) are penalized by 50% due to our efforts to build in efficiencies by decreasing our size. So an appeal went out to the USGBC to allow us to include our unconditioned basement in our house size, they allowed it. The only requirement is that we redo the energy model including a whole house air change, thus the second visit for a blower door test. Fortunately the results are pretty good, now including the air volume of the basement our ACH50 is about 2.3, so we should do alright on the second run of the energy model.

The reason we are here to begin with is that we did not meet a couple of prerequisites. There are two paths through the LEED energy evaluation, an energy model, or an itemized path… We are disqualified from the itemized path because we have way over the maximum 18% window to floor area ratio, opting instead for the comfort and energy savings of ample natural light. This leaves us with the energy model, however due to the size of our house, we opted for cadet heaters rather than a mini-split heat pump system that would have been grossly over sized. This breaks another prerequisite, one that requires our heat system (if using electricity) be at least 250% efficient. We were able to successfully appeal this because due to the size of our house, a large heat pump would be inappropriate and inefficient.

New Plants

This last weekend we had a good score with plants for our yard. A friend of ours is getting some yard work done, and her landscape designer ended up with piles of plants that he was selling off for $0.50 a piece, so we stocked up on creeping thyme, and an assortment of natives like salal and sword ferns.

Our Siding

We have really been enjoying the color changes that our house is going through, when dry it is beginning to silver, but when wet turns a deep rich red. No idea how long this will last, but we continue to be thrilled with our siding.

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