Daily Archives: May 8, 2012

Our house vs passivhaus / passive house

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.)

COMMENTS:
– 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.

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Filed under erik-green, passive house, zero energy home

2011/12: The year in heating

We have an emonitor gizmo that tracks our home energy use by circuit. One circuit is the air-source minisplit heat pump (the heat and cool in the house).

For the YEAR ending April 2012, the heatpump circuit shows:

3,009 KWh (total for year, heating and cooling and some hot water)
2,598 KWh (Oct-Apr — 7 mostly heating months)

Remember that we also heat our water with an air-to-water heat pump in the conditioned basement, so during the heating months, it is stealing heat from the house. So the 2598 includes some of that. Let’s pretend it is 10% of our total load (no idea) so that would be

2338 KWh (Oct-Apr — mostly heating months. HOME HEATING ONLY)

If we pretend the price we pay for electricity is $0.15/KWh (it’s more complicated than just a simple number like that with this and that charges) but close… then that is:

$350.70 (our estimated heating bill for winter 2011/2012)

Nice.

(Well, and actually… minus some significant fraction of that which is covered by our PVs (electric solar panels). We don’t have net metering, so our electric bill is rarely $0 even in the summer. I just don’t unclude the PVs cause I generally think of them as an offset. Not an important part of the house.)

SMALL IMPROVEMENTS “FOR SOMEDAY”:
– The silly 20KWh/month our minisplit uses whether it is on or not. Nothing to do about that at least in the winter. But I could flip the dip-switch for 5 months of the year.
– Someday I will add a submeter for the minisplits since the emonitor is probably 10% off in some direction. (I believe that’s the spec I’ve seen.)
– More PVs, perhaps this string with a central inverter and small battery for:     – night-time (since no net metering) and
    – power outages (we have a well so it would at LEAST be nice to have running water when the power goes out.)

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Filed under energy, energy-efficiency, erik-green, HVAC, passive house, superinsulation, zero energy home