DC-83-09-4 -- Ventilation Efficiencies of Wall-or-Window-Mounted Residential Air-to-Air Heat Exchangers PDF

Mechanical ventilation systems with air-to-air heat exchangers can be installed into residences to provide energy-efficient supplementary ventilation for the purpose of controlling indoor concentrations of contaminants, odors, and moisture. Wall-or window-mounted units have become particularly attractive because they are relatively inexpensive and easy to install. However, because they lack an air-distribution system, concern has arisen over their ventilation performance. To address this concern, a series of experiments was conducted on two different models of wall-or window-mounted heat exchangers. The nominal ventilation efficiencies of these units have been determined by measurement of tracer-gas decay rates at several indoor locations to be in the range of 0.47 to 0.66. No significant correlations between nominal ventilation efficiency and heat exchanger model or operational strategies were observed. Significantly higher local ventilation efficiencies were noted in the rooms where the heat exchangers were operating. Some preliminary tests indicate that internal leakage between the airstreams contributes significantly to the ventilation inefficiency of these systems.