Real heat recovery with air handling units

More and more air handling units are equipped with heat recovery systems, with the aim of decreasing the energy use in buildings for heating and cooling. The efficiency of the heat recovery system is often used to calculate the energy saving. However, air-handling units do not always function as planned. In particular, parasitic shortcuts and leakage may decrease dramatically the efficiency of ventilation and heat recovery. In addition, these units need electrical energy for fans, which may be more precious than saved heat. Measurements, using tracer gas dilution technique have detected various malfunctions in several units.