[Greenbuilding] Aggressively Passive: Building Homes to thePassive House Standard

[Rob Dickinson]

Interesting post, John.

I'm afraid I need clarification on a few points.

If I understand correctly, in PH you can't increase the amount of total kWHs
available by adding a solar PV array beyond the energy allotment specified
by 120kWh/m2/yr.  To me, this makes some sense because it avoids the
examples of very inefficient houses compensating by installing enormous
solar PV arrays.

But if one had an all-electric house and the exact amount of electricity
allowed by the area formula (i.e. 120 kWh/m2/yr) were produced on-site using
PV, wouldn't that that be more of a 1:1 source energy/site energy, and allow
the full 120kWh/m2/yr?   That would seem sensible.  Or is PH not that
sensible?

Hopefully I have expressed my question clearly.  I look forward to a
response.

Rob


On Sun, Jan 9, 2011 at 5:44 PM, John Straube <jfstraube at gmail.com> wrote:

> No, Bob, PH is both smarter and dumber than that.
> The energy metric is based on source energy: that is energy that feeds an
> electric plant, or the gas used to transport and compress natural gas.
> So if you house was all electric, it would be limited to 42 kWh/m2/yr
> because the electricity grid in Germany requires 2.7 units of energy for
> every unit of electricity (this is 3.35 in the United States, but the PHIUS
> uses the ratio for the German power grid: no I am not making this up).
> This is what PH uses, as does the Department of Energy.
> The other thing is that your 1500 square foot house, would not be 139
> square meters, as you need to subtract walls and stairwells and a few other
> things. So your house would become 105 or 110 m2.  Yeah, I know, odd.
> Net effect is you would be allowed to use 4000-4500 kWh/yr if an
> all-electric house.  This  could be 2500 kWh/yr of electricity and 5000
> kWh/yr of natural gas energy (170 therms).  You can use passive solar and
> active heating or air/water, but not active generation of electricity.
> For a family of four, 2000 kWh of electricity and 170 therms of gas is no
> mean feat.
>
> The easy way to meet the 120 kWh/m2/yr source energy is to build a larger
> house.  If you house was say 4000 sq ft (about 3000 sq ft measured by PH)
> you could use 6000 kWh of electricity and 680 therm of gas, which is about
> half (50%) the energy the average current house uses in the US, and about
> 30% less than a new code built home of your size.
>
>
>
> On 2011-01-09, at 5:47 PM, Bob Waldrop wrote:
>
> > ----- Original Message ----- From: John Straube
> > >area based energy metric (120 kWh/m2/yr)
> >
> > This is the standard for the passive haus?  Hmmm, for a 1500 sq ft house
> (1500/10.76 = 139.4 sq meters, times 120 = 16,728 kwh/yr, we do better than
> that with our amateur redneck extreme green  house.
> >
> > Bob Waldrop, OKC
> >
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> Dr John Straube, P.Eng.
> Associate Professor
> University of Waterloo
> Dept of Civil Eng. & School of Architecture
> www.buildingscience.com
>
>
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