One year results

Our final PHPP analysis from 11/22/2010 predicted (I think) that we/our almost passivhaus house would use (for one year) 1,741 * 27 * .293 (kBTU into KWh) = 13,773 KWh. But we used ~10,000 KWh. And this was with extra people for several months. And our solar panels made ~8400 KWh. So not net zero source energy but close (as I expected.) For the year 6/1/2010 thru 5/30/2011.

EDIT: Whoa, I was reading the PHPP excel file wrong. The right number to look at is the “Specific Primary Energy Demand” on the Verification sheet. Which for us was 39.1 kBTU/sqft in PHPP. So 1741 * 39.1 * .293 = 19,945 KWh. WHAT??!! This is twice as much as the 10,000 KWh we actually used. What is wrong with PHPP I can’t say. Anyway, interesting. The passivhaus “certificate” requires 38 kBTU and we used 10000 / 1741 / .293 = 19.6 kBTU/sqft so that’s roughly half the requirement. Huh.

EDIT2: hold on hold on. This is surely a site vs source (primary) eneregy issue. The 10,000 KWh is energy used at our home in electricity. So to make that electricity at the source/power plant it requires a much greater amount of fossil fuel (typically 3x, but perhaps averaged to less across all sources, if that is what is being used (and elec power plants do use a lot of fossil fuels and nukes in New England). So I will have to read about how PHPP does this, but that is surely why the PHPP estimate for “Specific Primary Energy Demand” is much higher. I suspect.

For the most part, extra people in the house doesn’t matter much. I think it’s only extra hot water use. Which is substantial enough. About $10/month (/$.15/Kwh * 12 ~= 804 KWh/year). We don’t use much hot water compared to most people I guess??? Oh, and maybe running the HRV on a slightly higher speed. Which during the winter would matter more.

I should add that, while I don’t have accurate numbers since our eMonitor was malfunctioning for 1/2 the year, my best guess is the following breakdown:

10,000 Kwh ~= $1,500 in electricity at 15 cents/KWh
of which…
$550 heat
$150 hot water
$800 everything else (lighting/appliances/cooking/well pump/filters/lawn mowing w/ electric mower)

If I am approximately right, then I think it’s probably fair to say that we used approximately 1/5th the amount of energy to heat our house compared to a typical new house of this size. $500 instead of $2500. Just a rough guesstimation.


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