BTW, as a followup to my last post. Our house misses the passivhaus PHPP standard for Specific Space Heat Demand.
= 4.75*1000*1741/(3412) = 2423 KWh used per year is what the PH Certificate requires as a max for “Specific Space Heat Demand” (for our 1741/sqft TFA)
Give that we *used* an estimated 2300 KWh (2338) for heating, and given we can estimate our (non hyperheat/h2i) heat pumps at 2.25 COP overall (as a 15% adjustment from the “North Carolina” temp zone rating–I think I looked up once for our unit’s seasonal HSPF… 15% adjustment: as they seem to do in Canada since the COP is temp dependent.)
That would be:
5260 KWh of actual heat *delivered* from the 2338 KWh our minisplits *used*.
So we are 1/2 or 1/3 as good as a passive house I guess. Probably 1/3 since it was a mild winter.
So you can see why people think passivhaus might be extreme. We are talking about $350 (our house) vs $120 (a similar-sized passivhaus) in heating given $0.15/KWh electricity. I still think it makes sense, especially since people are getting practiced at doing it panelized/modular. (See Green Mountain Habitat for Humanity in VT for example.)
- roughly 68F max in winter, roughly 78F max in summer
- I should do a per HDD calc
FUDGE FACTORS (+ or -) in my “1/2 or 1/3 as good as a Passivhaus” calc:
- Weather/climate in PHPP is a 30-year avg. This 2011/2012 winter was mild.
- COP of our heat pump is a guess (maybe I guessed way too low?)
- Previously mentioned guess for % (10%) of heat used for hot water heating
- Some inaccuracy of the emonitor device (vs direct submetering)
- Any errors made in the PHPP (our house used a number of non-certified products… windows, HRV so guesses had to be made)
- Related to above… our windows and HRV are also not as efficient as those typically used in a passivhaus.
That said, obviously there are some houses that don’t use Passivhaus” equipment — like this one — that do MUCH better than the PH standard. Occupant behavior matters a lot.