Wednesday, July 7, 2010

Men in Tights

Today Chris Conway, our EarthCraft technical advisor, did our final blower door test, to determine the air tightness of our house.

"Tightness" is measured in air changes per hour at 50 Pascals of air pressure difference (ACH50); the idea is to measure how often the air inside the house is exchanged with the outside if the pressure outside the house is 50 Pascals higher than inside the house. In other words, it's a measure of how quickly a house "leaks" air. (That's what a blower door simulates: it sucks air out of the house at a given rate to create pressure differential, and then measures the difference in pressure between inside and outside.)

A "1" means that the entire air inside the house is exchanged with the outside once every hour. A "0.5" means that the entire air inside the house is exchanged with the outside one-half times every hour (or once every two hours). A "0" means that the entire air inside the house is exchanged with the outside zero times every hour (never). So the closer to zero, the tighter the house.

Our house is a 0.09.

To put this in perspective, EarthCraft guidelines require any EarthCraft certified house to have a 0.5 or lower. If, like us, you are aiming for the top tier of EarthCraft certification, your house has to be a 0.4 or lower. If your house is a 0.25 or better, EarthCraft requires a method of fresh air ventilation (an Energy Recovery Ventilator, for instance). So, 0.09 is pretty darn tight: in other words, the inside air is completely exchanged with the outside about every 11 hours. Chris thinks it's certainly the tightest house in Virginia.

Now, a few pictures. The blower door ...

... and the tester that shows you the pressure difference (at left, in Pascals) and the leakage rate (at right, in cubic feet per minute - which is then converted, using the house's interior air volume, into ACH50):

Tuesday, July 6, 2010

Heat Wave

For those who are curious, our house is cooler inside than outside. And we're still glad we did not install air conditioning. I will admit, though, that some days in the house are a bit uncomfortable

You'd think the record heat in June would have pressured us to buy the awnings and insulated draperies to block the sun, but we haven't decided on style, color, etc. yet. So when it was 98 degrees in Falls Church yesterday, our house made it up to 87 degrees. That was a bit warm for me. But it cooled down to 78 in the house overnight and with the ceiling fan, it was quite comfortable for sleeping.

Today's Washington Business Journal news summary headline states, "
Cooling costs in Northern Virginia up 55%." (See the story at: Not our house! Our electricity utilization has gone up slightly since I put a dehumidifier in the basement, but much, much less energy is required than the typical house since we have no air conditioning!