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Two types to consider: Heat Recovery Ventilators (HRV) and Energy Recovery Ventilators (ERV). Which one is right?
Models that exchange moisture between the two air streams are referred to as Energy Recovery Ventilators (ERVs). ERVs are often recommended in hot climates where cooling loads place strong demands on HVAC systems. However, keep in mind that ERVs are not dehumidifiers.They transfer moisture from the humid air stream (incoming outdoor air in the summer) to the exhaust air stream.
Although some window or wall mounted units are available, HRVs and ERVs are most often designed as ducted whole-house systems. The heat exchanger is the heart of an HRV, usually consisting of a cube-shaped transfer unit made from special conductive materials. Incoming and outgoing air flows pass through different sides of the cube (but are not mixed), allowing conditioned exhaust air to raise or lower the temperature of incoming fresh air.
In cold climates, better air flow and the introduction of humidity to the indoor environment can help control wintertime window condensation. In humid summer climates, it can be advantageous to dry out incoming air so that mildew or mold does not develop in ductwork.
After passing through the heat exchanger,the warmed or cooled fresh air goes through the HVAC air handler, or may be sent directly to various rooms. Stale air from return ducts pre-conditions the incoming flow before exiting. Many systems include filters to further control contaminants that would otherwise re-circulate through the home.
For more information see EPA’s Indoor Air Quality site.