Air-tightness at MDH

We have been anxiously waiting to report our utility data from McKeesport Downtown Housing. Despite not passing the air tightness test, we anticipated a positive outcome for energy savings:  even with the new real air-tightness numbers, we hit the energy use targets. The contractor had done an excellent job with air tightness (we were at 2 ACH @ 50 pascals instead of our target of 1 ACH @ 50 pascals for a Passive House retrofit) and we really wanted to understand the effect this had on energy costs. We wanted to understand, in a more tangible way, what 1 ACH extra air leakage really meant.

Circumstances for our blower door testing were not ideal. The building was partially occupied throughout construction. We were able to test a few individual units during construction, but this wasn't helpful in predicting whole building air-tightness. During our final blower door test, the building was filled with residents, many of whom have mental health issues. We were not confident that all windows were closed and latched.  We had only a few hours to conduct the test.  We suspected that our test results were inaccurate, but re-testing would have been disruptive to the residents and owner; so we had to live with the results.

The image below shows Michael standing in front of the project with a card that is orange and blue. The amount shown in blue is the amount of air-leakage for the building allowed by Passive House. The amount shown in orange is the amount by which we missed that target. Now imagine putting that area in orange in a paper shredder, toss it around the building, and find the tiny leaks all over the 65,000 square foot building. The area shown in blue points out how rigorous the Passive House standard is for air-tightness and how much every little bit matters!

The moral of the story... don't order a second blower door test for a retrofit, if you don't pass the first one, unless you know exactly where the problem is. If you haven't been able to identify the source of the leaks with smoke sticks and a blower door, then chances are you won't find them.