Reach this level of air tightness requires a lot of attention to the details. In our case we have blower door that we can use in conjunction with the air sealing process to measure how tight the house is. The blower door is used to evacuate the house and create negative pressure within the house and drawing in air from any point and with the manometer you can measure just how much air is coming in uncontrolled. Making it simple to find the leaks and seal them before the drywall goes on. To reach the passive house standard the blower door number needed to be below 290cfm @50 and you can see from the picture we reached that number.
Once you reach this high level of tightness, you need to provide the correct amount of fresh air into the house, we need air to live right? But how much, and do we need and do we really want it to just leak into our homes wherever it wants? Well, we know how much fresh air is needed to maintain healthy indoor air quality, a simple calculation based on how many people live in the house and how big it is. Once that is determined we want to make sure we control how that air moves into the house and how much. To do this we use a ventilation system called, Heat recovery ventilation. For most of the houses we build, this means a dedicated system of duct work to various locations in the house to move air in and out of the house. The system is much like a car radiator, in that air moves across the radiator in one direction and warms the fins. The ventilation system works much in the same way. The air is drawn out of the house in the moist locations, bathrooms, kitchen, laundry and it crosses over a radiator in one direction, warming it (in the winter). At the same time fresh air is drawn into the house and crosses over the radiator in a different direction, picking up some of the heat and transferring it into the fresh air. 65-75% of the heat can be recovered and the fresh air now coming into the home isn't just cold air but prewarmed with the air going out. We place the incoming air into the living portions of the house, living room, bedrooms, dining room.
That's some of the technical stuff but experiencing a house like this is something you have to see to believe. Last Wednesday is was a cold blustery day the daytime high temp was about 23F with a 20 MPH wind most of the day. The wind chill in the morning was a bone numbing -6F. The house with no heat was 39F and warmed quickly with the sun shine we had that day. But what really got me was when you opened the door, no air came into the house. You could step out of the door and instantly feel the blast of cold but step just inside and you didn't even know the wind was blowing. It is really that pronounced one simple step from inside to out and the temperature dropped some 30 degrees and the wind would bite you face. Step back in with the door open and you felt nothing. Pretty cool stuff that amazes me every time we build one of these super insulated homes. Something you have to see to believe.
Stay tuned
Tom Pittsley
