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Old 01-01-2019, 04:41 AM   #14
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Originally Posted by DickR View Post
I used AMHVAC (Bob Maher) in Moultonborough for the heat pump & zoned duct work installation, plus the HRV. It was his first GSHP installation (IIRC), but this wasn't particularly hard to do. I already had sized the unit and had it delivered. The lines to/from the well were in place already from the well drilling crew's part, and the rest was just ductwork and zone setup. I had the manuals and did my own tweaking of DIP switch settings on the heat pump to ensure it ran the way I wanted it.

The HRV is a Lifebreath ECM195 ( It has a pair of cross-flow heat exchanger cores, for high heat recovery. The HRV is in the utility space at the back half of the lower level, suspended from the ceiling joists, with clearance to walk under it. There is one insulated duct from a hood outside the house bringing fresh air to the HRV, and another for the outgoing air from the HRV to a separate hood outside the house and around the corner from where the inlet hood is located. Fresh inlet air, warmed by the outgoing air, is ducted to the heating system return duct. Thus fresh air flows through the heat pump, even when it isn't on, and out through the ductwork to all parts of the house. There is a separate set of ducts drawing from each of the bathrooms, plus one from a corner of the kitchen well removed from the range. These come together and pass through the HRV on the way to the exit hood. There are 20-minute booster timers in each of the bathrooms, which turn the HRV fan rate to high speed during and following use of showers. Otherwise the HRV is set to run at low speed 24/7 (around 65 cfm), which gives fresh air flow roughly in accordance with ASHRE 62.2 guidelines in place at the time.

The ideal way of installing an HRV is by using a dedicated system of small diameter ducts for distribution of the fresh air to the house, particularly to bedrooms. But as long as there is reasonable distribution of the incoming air, such as through existing ductwork, the system ought to work fairly well. My setup does not have dedicated distribution ducts, but the overall result is quite good, I feel. Interior air is kept down to low 30s (%RH) in winter, within range of comfort for most people, and the occasional introduction of cooking odors not handled by the range hood is flushed out reasonably fast (like overnight).

There is one thing to plan for, disposition of condensate from the HRV. In winter, the fresh air coming in is quite cold, below the dew point of the interior air. As the incoming air is warmed by the outgoing air, the latter of course is cooled considerably, producing condensate.
In my installation, the condensate passes through a trap, then down through a hole bored in the basement slab. Otherwise it could flow by gravity or pump to a utility sink, if present.
In less-frozen areas of the country, condensate is routed to a barrel, where it is collected for use in gardens. (Or run from a barrel through a hose directly to needy plantings).
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