The glycol fluid removes heat from hot exhaust air streams and rejects the heat into a cold make-up air stream . This coil-type exchanger has the advantage of permitting heat transfer between supply and exhaust systems in widely separated portions of a building. Unlike conventional heat exchangers which only transfer heat, the ability of an enthalpy exchanger to transfer moisture means that both sensible and latent heat is transferred. Energy conservation results from reducing the cooling load on the air conditioning system by reducing the humidity of incoming air. By recovering some of this latent heat, enthalpy exchangers can maintain dehumidified fresh outdoor air in summer and a comfortable humidity level of fresh outdoor air in winter.
Payback periods depend on the hours of operation and severity of climate zones.
An important consideration should be the downsizing of heating and cooling equipment and the reduction in peak load energy demand. Financial evaluations may also include the elimination of dehumidification and humidification costs if a latent recovery technology is employed. Typical paybacks in Michigan range from 2 to 7 years. Other HRUs are available as ducted energy recovery ventilators for commercial and institutional use. In all cases where energy recovery technology is employed, significant reductions in heating and cooling equipment size can be expected, since design-day ventilation loads are reduced.