Frosting of rotary air-to-air heat exchangers is a problem that exists in locations where winter ambient temperatures drop below the ice point.

This paper correlates the experimental work conducted at the University of Manitoba from 1973 to 1975 with a theoretical means of predicting when frosting may be expected. The work was conducted on a hygroscopic (total enthalpy) exchanger. The results are applicable to both design and operation of rotary air-to-air heat exchangers.