Evaluation of an air-to-air heat exchanger

A room-size, residential air-to-air heat exchanger was tested for effectiveness of heat recovery. The experiments were conducted in a small (16.6 m3), wood frame building, the Test Chamber, on the roof of a laboratory building. The Test Chamber is a controlled and instrumented structure for which we have the ability to predict within 1% the heat loss rate over a 6-h nighttime period. With the heat exchanger installed and operating in the Test Chamber, the heat recovery efficiency was determined by comparing the actual heat loss to that expected due to the mechanically induced ventilation. The heat exchanger recovered almost 50% of the heat contained in the outgoing air flow. Additional experiments quantified effects of fan power consumption and heat conduction through the case of the device. By considering these effects, we determined that the heat exchanger itself works at an efficiency less than the manufacturer's claim. Conducting the experiments in a real building has provided insights and evaluations not possible in an indoor laboratory.