If you are designing for air-to-air energy recovery, there is a valid argument for selecting the most efficient design.
Where previously, rotary wheels were predominately used in built up plantrooms, consultants now have the option to specify their inclusion in prefabricated packaged equipment. Incorporating rotary wheels with high efficient fans, controls, filters and additional heating or cooling coils all in one unit, consultants can confidently select a packaged solution that is also simple to install.
The key to the high efficiency of rotary heat wheels is the ability to process large volumes of air, combined with effective heat storage mass, allowing energy exchange efficiency of up to 85%.
Rotary heat exchangers have a wheel-like construction, made of aluminium foil, featuring countless small channels through which the air flows and transfers heat to this storage mass. Aluminium is ideal for this process because of its high thermal conductivity.
The heat wheel rotates between two air currents: that of the supply air, which brings external air inside the building and the exhaust air, which carries ‘used’ indoor air outside. The air from outside flows through half the storage mass, while the exhaust air traverses the other half.
Through this process, in winter conditions, instead of the incoming fresh air just forcing warm air to be being exhausted straight to the outdoors, the majority of the exhaust air heat is transmitted to the storage mass. This warmed half of the wheel continues to rotate until it is in the path of the cooler supply air, to which it transmits its heat. Consequently, the supply air enters the building at a significantly higher temperature.
In summer, the principle operates in reverse. The exhaust air is cooler than the incoming air. The rotor stores the lower temperature of the exhaust air and so cools the warm air entering from out-side.
With variable speed motors, the rotation speed can be adjusted, and combined with temperature sensors a rotary heat wheel can be slowed or even stopped to take advantage of changing outdoor climatic changes, providing an effective an ‘economy cycle’ option.
