ACH50 Metric for Measuring Energy Efficiency
I just read your article questioning the use of air changes per hour as the metric for measuring energy efficiency versus air leakage as a percentage of wall area. There were several remarks in the article that it wasn’t fair to smaller buildings.
Ill start by saying that it is the air volume in the building that has to be heated and when energy escapes from the building in the air volume, it has to be replaced.
the comments about fairness is about as relavant as saying it’s not fair that gravity makes things fall down, Sorry that’s just the way things are. As objects get bigger their ratio of surface area to volume decreases. A wooly mammoth has a lower energy requirement per pound then a mouse. It’s probably why the size of species increased during the ice ages. Is it really about fairness.?
On a related issue I did an analysis of cost per square foot of different building sizes to lockup stage. A 10×16 shed is about 3 times more expensive Per Square Foot then a 1000 square foot home. Bad news for the tiny house movement. The efficiency of size is a very relevant issue . It’s much harder to meet the passive house standard in a house under 1000 sq ft. But the house is smaller and therefore could use less energy than a larger one overall. Should we measure per living unit, ie person or dog. Perhaps by living weight of occupants?
I’m willing to stick to ACH for now.
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You've hit on a big criticism of both energy codes and certification schemes like LEED, in that they're process-oriented and not outcome-oriented. It's kind of crazy that the energy code allows you to have as many skylights as you want -- but they have to be low-U.
Joe Lstiburek likes to point out that under LEED, if you install an Energy Star dishwasher that uses four gallons of water per load instead of a regular one that uses six gallons per load you get one LEED point. But if you have a swimming pool that uses 10,000 gallons every time you fill it you don't lose any LEED points.