One of the qualities of a Passive House is that the construction is nearly airtight., so to allow the house to “breathe” we use an energy-recovery-ventilator (or heat-recovery ventilator). Yes, houses need to “breathe”, or more accurately, people inside houses need fresh air, but the problems with leaky construction are at least threefold: 1.) you don’t know if the leaks are getting fresh air where you need it (like in the bedrooms), 2.) as it leaks in, the air picks up contaminants and can cause condensation, mold, and deterioration of the structure; and 3.) you don’t know the rate of “leaking”, so combustion gases, moisture, etc. may not be getting cleared out of your house. My analogy is that we want the beast to breathe through its nostrils, not through gaps in its skin.
Like all Passive Houses, ours has a balanced ventilation system (same amount of supply and exhaust) that runs continuously. It has an extremely efficient fan, and recaptures about 85% of the outgoing heat, so it is a low-energy way of providing great indoor quality. The system extracts air from the kitchen, bathrooms, laundry, basically any place that makes moisture and odors, and supplies fresh air to bedrooms and other living spaces. Imagine getting fresh air continuously as you sleep…you wake more refreshed, having been breathing air that was cleaned of pollen and molds by the (MERV 7/8) filter.
|Zehnder, beginning of installation|
Our system is a Zehnder ComfoAir 550. Zehnder not only has great heat recovery technology, but they have also developed a suite of products that make sizing, installation, and commissioning (getting air flow right) a breeze. The small flexible ducts clip into supply and exhaust manifolds, and into supply and return diffusers, which have fittings to adjust flow rates.
|Zehnder with ductwork connected to supply and exhaust manifolds|
These ducts are flexible and fit in a standard 2×4 cavity, so are quite easy to work into the construction site (though I recommend a riser for ducts running from the manifolds to another floor). One reason each diffuser is individually ducted is that precise airflow can be guaranteed at each location. Commissioning consists of testing each diffuser at the end of installation and adjusting the unit’s fans and the diffusers themselves to ensure design flow rates. Once set, it typically doesn’t take maintenance to maintain the flow rates; all that needs to be done is occasional cleaning of the filters. Clean, fresh, healthy air, 24/7.