Heat Recovery Ventilation (HRV) systems/units are used when you want to introduce large amounts of outside air into an occupied environment. Simply stated, the HRV systems mixe ambient air from inside the home or building with outside air, uses the energy from the inside air through an exchanger to condition the air (heat it up if used in winter months) so the air coming into the home or heating/cooing system is closer to ambient temperatures. The HRV systems/units can move from 50 CFM up to 200 CFM and higher depending upon the size of the unit. Most HRV systems used in the residential market introduce between 100 and 200 CFM. The conditioned air is usually brought into the return air duct side of the HVAC system, although it can be introduced into the supply side.
ERV Systems / Units
Energy Recovery Ventilation (ERV) systems/units are also used to introduce outside air, although they are capable of bringing in much larger amounts. Also, the ERV systems use a rotating wheel made from a variety of materials such as ceramics or polymers. Again, this type of air exchanger system is installed in the same way as the HRV unit. ERV systems/units are more efficient than the HRV units but they are also more expensive. ERV units are more commonly used in the commercial market. Both HRV & ERV units have minimal air filtration capability so additional filtration is required.