Here we share some observations about and snapshots of the Passive House we had built in Oakland County, Michigan. All photographs were taken by us unless otherwise noted.

Our house is provided with fresh air by means of an energy recovery ventilator (ERV), in our case a Zehnder ComfoAir 350, an outstanding system on every count. These units work by running stale, room temperature outbound air through a cross-current heat exchanger to warm and humidify (in winter) or cool and dehumidify (in summer) inbound fresh air. Since the energy recovery isn’t completely perfect, we condition our interior air when needed with a couple of Mitsubishi minisplits. The problem with this arrangement is that the air warmed or cooled by the minisplits tends not to diffuse uniformly throughout the house. Instead, it drifts toward the bathrooms and kitchen where the ERV’s intake registers are located and away from the rooms where the fresh air from the ERV is supplied.

Zehnder makes a product that can help with this issue. It is the ComfoFond, a geothermal preconditioner system that works with the ComfoAir. Fresh air runs past thermal transfer tubing in the preconditioner before entering the ERV. This will effectively warm the inbound air in winter and cool and dehumidify the inbound air in summer. According to Zehnder’s documentation, for our climate where the ground temperature is 55°F, air entering the preconditioner at 10°F will leave it at at 34°F. Air entering at 95°F will leave it at 77°F. This should take a burden off of the ERV and reduce the times when we need to use the minisplits.

The ground loop we installed is 400 feet of 1 inch diameter hePEX. At its deepest the tubing is below the water table where thermal conductivity is increased.