Thermal Wheel

A thermal wheel, also called a rotary heat exchanger, recovers heat between the supply and exhaust air streams of an air handling unit using a rotating porous metal wheel as a thermal storage medium, which picks up heat as it turns through the warmer air stream and releases it into the colder one. Positioning the two air streams so they flow in opposite directions across the wheel gets the most heat exchange out of the temperature difference between them, and the device needs only a small motor to keep it turning, which makes it an economical way to recover waste heat from exhaust air and warm incoming fresh air in building climate control systems. Under standard conditions a thermal wheel reaches a sensible heat recovery efficiency of about 85 percent, and enthalpy or desiccant variants that also transfer moisture between the streams can add a further 10 to 15 percent. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/