Air to air energy recovery heat exchangers (ERHXs)

Several configurations of air to air ERHXs exist, they include heat recovery ventilators and energy recovery ventilators. They are placed in ventilation units, unitary air conditioners, and air-handling units that take in outdoor air while venting indoor air.
Those air to air energy recovery heat exchangers reduce HVAC energy consumption and reduce the required air-conditioning capacity of the building too.
But a periodic cleaning to maintain effectiveness is necessary. During the heating season in cold climates, a frosting protection may be necessary.