Most energy-efficient homes include a mechanical ventilation system — often an HRV or ERV that brings in fresh outdoor air while simultaneously exhausting an equal volume of stale indoor air. The main problem with introducing outdoor air into a house is that the air is at the wrong temperature — too cold during the winter and too hot (and often too humid) during the summer.
HRVs and ERVs address this problem by passing the outdoor air through a heat-exchange core designed to take the edge off extreme temperatures. (For more information on this type of ventilation system, see HRV or ERV?) While the tempering function of the heat-exchange core helps, it isn’t a perfect solution. Unless the outdoor air is already at room temperature, the air delivered by an HRV or an ERV will always be cool in the winter and warm in the summer. Moreover, in cold conditions an HRV core starts accumulating ice. Manufacturers have developed a variety of solutions to the frost problem. For example, a cold HRV core can be warmed by temporarily closing the outdoor air damper and circulating indoor air through the core (that is, by putting the HRV into “recirculation” or “exhaust only” mode). Another way to address ice buildup is to include an electric resistance heater that raises the temperature of the incoming outdoor air.
Some HRV and ERV manufacturers (including Zehnder and Ultimate Air) offer a third option: a system which conditions incoming outdoor air by blowing it through copper heat-exchange coils connected to a buried ground loop. This buried ground loop consists of hundreds of feet of PEX tubing (usually between 3/4 inch and 1 1/4 inch in diameter) filled with a glycol solution; operation of the system requires a pump to circulate the…
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