Maine Passive House: How Low Can He Go?
Chris Corson and EcoCor Builders wrapped up the company's first Passive House project in Knox, Maine, this month. "We're 100% complete," said Corson on January 21. "I just have to go out today and conduct the final multi-point blower door test, and have all the paperwork signed for the end of the job, so Daddy can get paid. They are moving in on Sunday."
As a satisfying last step, a two-man crew from Maine-based Revision Energy set seven 200-watt solar panels into brackets on the south side of the house (see image below). Located on the south wall, the panels will shade the lower tier of south-facing windows in summer, but will still get full sun themselves. And because they're mounted close to the ground instead of on the roof, the owners will be able to keep them clear of snow using a long-handled roof rake, Corson points out. Given the home's extremely low power needs, the panel array is enough to make the house net-zero on an annual basis, says Corson — although, as he notes, "It all hinges on occupant behavior. If they decide they want to leave the windows open all the time, all bets are off."
Squeezing the panels into the home's tight budget took a little creativity. The new homeowners, Matt and Heather Diko, paid for kitchen appliances out of pocket instead of out of their construction loan as planned, and they agreed to sign over their $2,000 Maine rebate for the panels to Corson so that he could pay for the panels up front. And Corson himself even took a $1,000 cut in the job's profit in order to be able to fit the solar array into the home's $210,000 price tag.
"It's worth it to me," says Corson, "in order to have a total showcase project. And the homeowners also agreed to let me data-log the home's performance over the next few years, which will give me information to make my next houses even better."
Corson's final blower door testing, with a new blower door, showed the house easily clearing the official Passive House standard (0.6 ACH-50). After sealing off the energy-recovery ventilator's exhaust and intake ducts and the heat-pump air handler, though, Corson was frustrated when the latest test did not reach the very low 0.37 ACH-50 he had scored on an earlier test using a different blower door. But as he turned his attention to sealing cracks in the blower door itself, and sealing the device to the house door opening, the numbers dropped down toward the earlier score.
The process revealed a unique problem with Passive House performance verification: the precision and reliability of typical diagnostic equipment lacks the sensitivity to measure performance at such an advanced level. Blower door equipment is commonly used in verifying Energy Star performance, for example — but Energy Star allows air leakage 10 or 20 times higher than Corson is trying to achieve. Corson stopped his blower door down to the smallest opening it allowed — in a conventional house, he said, "This is what you would do to blower-door test a bathroom." Even so, the biggest air-sealing issues the test revealed involved the blower door itself.
Setting up and measuring the home's final blower door tests with a brand new blower door. Turns out, the blower door itself needed sealing.
Corson says he's trying to beat the Passive House standard with room to spare. He's shooting for 0.3 ACH-50 instead 0.6 ACH-50. That way, he says, he'll have the confidence to play with different solutions in both the affordable market and the high-end market. (Already, EcoCor has two passive house projects lined up for 2012.) "This is a simple house," Corson says, "but I need to be sure that I can pass the standard even on houses with complex shapes, bump-outs, dormers, et cetera. And for affordable houses like this one, if I can make them even tighter than the standard, I can trade that off and reduce my insulation costs and still heat the building with a 1500-watt heat pump."
That goal, says Corson, is why he continues to strive for a more accurate and sensitive blower door technology. "Next time I'm going to use a small duct blaster fan instead of this big fan," he says. "And I'm going to seal it into a piece of plywood instead of using this porous canvas. I need the accurate numbers for myself, and I need them for other people also. I can't tell Katrin Klingenberg [the Passive House Institute U.S. director], ‘Yeah, I scored a 0.5 ACH-50, but I know it's really a 0.25.' I need to be able to document it."
