Plugging Air Leaks Would Save Billions
Researchers say that bringing U.S. homes to a uniform level of airtightness could save $33 billion in energy costs annually
Bringing all U.S. homes to airtightness levels spelled out in the 2012 International Energy Conservation Code would save as much as $33 billion in energy costs annually, according to new research at the Lawrence Berkeley National Laboratory.
Berkeley Lab scientist Jennifer Logue, lead author of the study, and her fellow researchers used "physics-based modeling" to calculate how much energy is wasted by air leaks, Berkeley Lab said in a news release. Researchers also wanted to identify a standard of airtightness that represented the best balance between costs and energy savings.
Researchers considered five levels of tightening:
- "Average" tightening, which researchers defined as meeting levels of both the Weatherization Assistance Program and other non-WAP energy retrofit programs for an overall reduction in leakage of between 20% and 30%.
- "Advanced" tightening, in which all houses would be as airtight as the top 10% of houses with similar characteristics.
- Airtightness as defined by the 2012 International Energy Conservation Code, which is no more than 5 air changes per hour at a pressure difference of 50 pascals (ach50) in climates zones 1 and 2 and no more than 3 ach50 in climate zones 3 through 8.
- Canada's R-2000 standard, which is 1.5 ach50.
- The PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. standard of 0.6 ach50.
IECC standard offers the best balance
The total amount of source energy used in American homes is 22 quads (22 quadrillion BTUs) per year, or 23% of total U.S. consumption, the report says. Source energy includes the energy consumed on site plus the raw energy required to produce and deliver it.
Tightening every one of the country's 113 million homes to be as airtight as the top 10% of similar homes (what researchers called "advanced tightening") would save 2.6 quads of energy per year, or roughly $22 billion, the report said.
Getting to the IECC standard would save 3.83 quads, or $33 billion, annually. And that level offered most of the benefit of the two tighter standards while being more realistic to achieve. "According to their analysis, raising the U.S. housing stock to the IECC standard would reduce airflow in homes by a median value of 50 percent," the Lab said.
"As we move forward and look to build better housing stock, we want to know what standards we should enforce," Logue was quoted as saying. "It looks like the IECC standard gets us the majority of the benefit of air sealing. More research is needed to determine the cost of implementing each of these standards in new homes to see which are cost-effective. As we get better at air sealing we can move towards tighter envelopes in buildings."
Ventilation carries low energy penalty
Berkeley Lab said the study took into account the amount of energy that would be required to increase ventilation to meet the ASHRAE 62.2 standard for healthy indoor air.
"We found that the energy burden would be pretty small, only about an additional 0.2 quads of source energy annually to get everyone to the level where they're getting enough whole-house ventilation," Logue said in the press release.
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