On Saturday, our advisor and supplier, Malcolm Isaacs from the Canadian Passive House Institute, visited us again to carry out the second (and hopefully, final) blower door test on airtightness, and to do some final tweaks to the Heat Recovery Ventilation (HRV) system to make sure it is fully balanced.
On the latter issue, we discovered one curious thing: our ‘HRV’ actually appears to have an Energy Recovery Ventilation (ERV) core. This means it actually not only uses a heat exchanger to transfer heat from the outgoing care to the incoming air, thereby keeping the air in the house both warm and fresh, but also balances the humidity (for more on the differences, see this Ecohome.net article). This is interesting not least because we only paid for an HRV, so far as we know…
However, the big news is something much bigger. When Malcolm last visited to do our preliminary blower door test at the end of September, various things weren’t ready, in particular, we had a malfunctioning and only partly sealed Motura sliding door, and the equipment wasn’t able to accurately record the figures we needed so we could only get a rough result. Even then we got a pretty good indication that the house was already well inside the Passive House standard. In the meantime, the door had been properly sealed, and Malcolm had obtained the component that would allow for the test to be done more accurately.
As the house was being pressurized, we went around with a little camera that measures temperature differences, to check for air leaks. We also discovered that one of the HRV ducts that goes through the outside wall was not actually as sealed as it should have been, despite the gaps between it and the wall having been filled with sprayfoam. So we had to seal up the edges with some more of that expensive but very effective Siga tape.
The process of doing a blower door test is outlined in the blog entry about Malcolm’s previous visit. You need only recall that you pressurize the house to 50 Pascals, and then record the amount of air that has to be added to the house to maintain that pressure. From these numbers, with the house volume, you can calculate the Air Changes per Hour, or ach50. The highest Canadian Standard, R-2000, is 2. The Passive House standard is 0.6. Last time we’d measured just above 0.4.
Malcolm did his measurements and then went away to do the calculations back home. From here I’ll just quote directly from his e-mail to us today:
“I’ve just finished recalculating the blower door test results from my visit yesterday. We did not do too badly, with an overall n50 airtightness of 0.185 ACH @ 50 Pa for both overpressure and underpressure. To the best of my knowledge this house is the most airtight building in Ontario […] This result shows the high quality and performance of all components used in the house, as well as the significant extra efforts of each of us who worked on the airsealing. The impact on overall energy demand in PHPP [the software used for calculating Passive House performance] is very significant: it drops overall specific energy use from 14.6 kWh/m2y (assuming 0.6 ACH) to 12.5 kWh/m2y.”
For those of you who don’t speak Passive House, Malcolm provided a summary:
“Speaking as an engineer, we have a special technical term for this result: KICKASS.”