Most exchangers consist of a stack of ribbed plates. Heated air flows on one side of each plate, while cooler air flows on the other side of the plate. The warmer air heats the plate and transfers heat to the air on the cooler side. Heat exchangers themselves have no moving parts and can be located in any relatively clean air streams. Heat exchangers should be considered in new construction or renovation of bathroom, shower, kitchen, medical facilities and laboratories, dining and other building areas normally exhausted.
Heat exchangers work both directions, effectively reducing both heating and cooling loads.
In the winter, the warm exhaust air heats the incoming ventilation air. In summer the cooler inside air passes through the exchanger and cools the incoming ventilation air. Heat transfer from the warm side to the cool side of the exchanger depends on the amount of surface contact area per CFM of air moving through the exchanger. As a practical limit, increasing the amount of surface area past a certain size is not cost effective, depending on factors like material thickness and cost, energy cost, average temperature differences, and pressure losses. Basic formulas used in heat exchanger calculations.