How does the frost threshold temperature affect energy recovery wheels?

Frost formation causes reduction of airflow through the heat exchanger. Without frost control, energy recovery and airflow may be significantly reduced.

The frost threshold is the dewpoint temperature at or below freezing. 

As the exhaust air cools it reaches saturation. If this happens at or near freezing, frost may form on the wheel. This may block the airflow and reduce the effectiveness of the wheel. Excessive reduction in airflow may cause issues for the fan operation in addition to failure to meet design capacity and outside airflow requirements. AAON offers a solution within our controls with a selectable, simple defrost cycle. This option spins the wheel for a predetermined time then pauses it to allow the frost to dissipate before spinning again. Enabling this cycle maintains the effectiveness of the energy recovery wheel.