An air-to-air heat exchanger keeps indoor air fresh without wasting heat
Often, when people think of high performance homes, they assume this is a new and untested phenomenon. However, people have been living comfortably in high performance homes for decades now, and while there are many new technologies available on the market, a high performance home can feature time time-honored and proven systems that are both reliable and cost effective. We recently spent time with Bill and Bonnie Dripps of State College, PA, whose high performance home has kept them warm and comfortable since 1983.
How does it work?
The three key features of a high efficiency home, according to Bill, are insulation, sealing, and air exchange.
In their home, they used double walls - two insulated wood stud walls separated by a 3.5 inch insulated gap. "Most people think it's a crazy amount of insulation" says Dripps, but "All I can say is it works". Windows were specially chosen for their high thermal resistance, and have built in insulated shutters that slide in place at night to improve thermal efficiency. Attic and Basement insulation was similarly designed with generous insulation, even under the basement floor.
Sealing the house completely and absolutely is the second critical component to the home's design. "The living space is a gas tight bag" says Bill, who mentioned that at least 50 tubes of caulk were used to ensure that the house's vapor barrier is fully sealed. Windows, doors, and other penetrations in the wall had to be very carefully selected and precisely installed to make sure that the building's perimeter seal remains intact.
With such a tight seal on the house, you can imagine that moisture, odors and other gases could easily build up and cause problems. Thus, the third component in the design is a ventilation unit that provides fresh air to the interior and exhausts old air, but keeps most of the heat energy from leaving the house, using a device called an "air to air heat exchanger".
When these three components are properly designed, installed, and operated, the result is a very energy efficient house.
Does it pay off?
After nearly 35 years of living in their high efficiency home, Bill is absolutely convinced that this is the best way to go, and that it easily pays off - "The economics were so utterly compelling". Was it more expensive to build? Yes, a little. However, he found that the increase in his mortgage payment was more than offset by the decrease in his heating bill. Thus, his overall living costs have been lower from the very beginning. While high performance housing has a reputation of being for "high end" housing only, Bill contends that "This ought to be what the poor are building" as well.
What are the other benefits?
One thing you notice quickly after entering the home is just how comfortable it is. The high insulation levels result in warmer walls, which makes a room more pleasant and less drafty. "The increase in comfort is worth it in and of itself" says Bill, and Bonnie adds that "This is the first house I've ever been warm in" during the winter.
The other noticeable difference is how quiet the house is inside. Thick walls, careful sealing and high quality windows all result in remarkable acoustic isolation, which means that you can snooze in peace, blissfully unaware of the neighbor's noisy dachshund or clattering snowblower.
Bill said that the key to success with his home's design and construction was finding a builder with experience in high performance housing. "You have to do some things that most people don't think of", that don't match up with traditional construction methods. With that in mind, the final part of this series of articles will feature a talk with a builder who specializes in sustainable and high efficiency buildings.
Prepared by Daniel Ciolkosz, Penn State Extension, Department of Agricultural and Biological Engineering