I am conflicted… basically we want to build the cheapest, lowest BTU house possible.
But we also want to make a little noise and share info about what we have done.
So on the one hand the passive house would be nice because you can get a stamp of approval and with that the potential for news articles, etc!
But the practical engineer in me wonders if the overkill of getting from superinsulation to passive house — by adding 4″ of exterior rigid insulation, more expensive Thermotech windows, $4000 more in modeling and extra-special blower-door testing — is the “right” way to do it. Maybe it is though. What would 4″ of rigid cost and Thermotech casements cost? How many BTUs of heat would it save per year?
If *I* were coming up with the passive house standard, it would have a cost-effectiveness standard in it.
I would be asking (and I’m just looking at my BTU heat-loss/usage excel spreadsheet here…) how does one decide how to spend money… it seems like it should be something like MOST BTUs-saved (at the source) PER $$. And over at least 30 years.
So in the running would be…
1. hot water
2. electricity–appliance usage/”household operations”
3. HVAC — heating/cooling/ventilation
4. car usage (prius, bike, work at home, etc)
…and non house/car…
5. food (vegetarian, etc)
6. not buying stuff
a. better envelope (insulation/sealing/windows) (for #3)
b. solar hot water (for #1, maybe #3)
c. solar heating (sometimes also combined with #b) (for #3)
d. solar PVs (which can be used toward #1, 2, 3 and 4) and also has the benefit of generating during peak usage hours, so should be encouraged)
e. changing behavior (cooler house, changing eating, driving, turning stuff off, etc) (#1, 2, 3, 4, 5, 6)
f. smaller house
“Passive house” is a solution putting all ones eggs into one basket (#a above) without considering when the “$/KWh” (saved over 30 years let’s say) are lower coming from one of these methods of dealing with 1-6. (Sorry, I switched units and inverted from high BTUs/$ to low $/KWh — but I think the latter is nice because we know what we pay for a KWh of electricity. In Massachusetts it’s like $0.20-$0.25 if one is doing GreenUp/GreenStart for renewable electricity from the electricity company)
So sorry, looking just at the problems 1-4 and solutions a-d (things we can build/buy):
- #a (well, and #c) are unique in that they are best done when the house is built.
- #a also probably have the best lifetime–infinite. Well, except windows which need replacing in 15/30(?) years
But there are obviously diminishing returns with #a, so when do you shift to b, c, or d? And which?
Basically I’m just imagining our house plans as currently designed, but analyzing it without solar PVs or hot water added yet (just #a). My estimate is that we maybe need (in KWh per year) — these are items 1 thru 4 from above again:
1. 3100 hot water (based on some ridiculous guess of our usage)
2. 4200 appliances/lights
3. 3300 heat
4. 9700 car–our 25mpg Saab station wagon commuting to Sudbury Valley School 180 days
So even if we get heat to approach 0, we still have some HUGE numbers elsewhere.
I think it’s possible to price out a thru d and make a reasonable estimate as to the savings involved. My guess as to the rankings would be, from most bang for the buck to least (and it really doesn’t have to be guesses, these are all things which could be calculated, I think)
1. our current “superinsulation” package (12″ walls, 18″ ceilings, Marc Rosenbaum tightness standard 0.05 CFM50/sqft shell, triple pane Paradigm windows, solar tempering — extra window sqft on the south)
2. air-source heat pumps (Fujitsu 9RLQ times 3 maybe)
3. solar hot water
4. Prius (maybe plug-in)
6. passive house level of insulation
And I haven’t really looked into the cost, but I suspect that an active solar air-heating solution with a low-mass sunspace and insulated solar heated water storage for cloudy days (ala Norman Saunders, Nick Pine, et al) might contend with #2 and 3 in total cost, and get closer to 0 BTUs/year used for heating and hot water (pre-PVs) — supposedly 97% “if cloudy days are like coin flips”.