Numerical and Experimental Investigation on Frosting of Energy-Recovery Ventilator Stephane Bilodeau, Yves Mercadier, and Patrick Brousseau Universit~ de Sherbrooke , D~partement de g~nie m~canique, 2500, boul. UniversitY, Sherbrooke, (Quebec) J1K 2R1 Canada Abstract. Frosting of energy-recovery ventilators results in two major problems: increase of pressure losses and reduction of heat transfer rates. Frost formation of heat and mass exchangers used in these ventilation systems is investigated both experimentally and numerically. A numerical model for the prediction of the thermal behavior of the exchanger is presented. The model is validated with experimental data and is then employed to conduct a parametric study. Results indicate that the absolute humidity is the prevailing parameter for characterizing the frosting phenomenon. A frost-mass-fraction chart is established in terms of the absolute humidity of the warm exhaust stream and of the temperature of the cold supply stream. The effect of time and mass flowrate is also evaluated. The transient three- dimensional model shows that the absolute humidity and the temperature of both air flows vary nonlineaxly in the frosted zone. 1 Introduction Frosting of heat-recovery ventilators (HRV) and rotary heat and moisture exchangers (RHE) is frequently observed in cold climates. Frost builds up when the exhaust air stream from the exchanger is cooled below its dew point and moisture condenses on a cold surface below the freezing temperature. Frosting results in a reduction of the heat transfer rates and in an increase of the pressure losses through the heat exchanger. Hygroscopic air-to-air rotary heat exchangers transfer energy in both sens- ible and latent heat forms in a periodic adsorption-regeneration cycle. In the adsorption part, the dew point decreases as the exhaust air stream flows through the microchannels and gives off water to the desiccant. In the regen- eration part, the desiccant releases its humidity to the stream of dry air. Holmberg [1] as well as Pfeiffer and Hbner [2] have conducted experi- mental studies on the frosting phenomenon during the operation of rotary regenerators. Frosting of such exchangers has also been investigated numer- ically by Attia and D'Silva [3] and by Stiesh et al. [4]. In both models, heat transfer was two-dimensional and the underlying mechanisms of frost form- ation were ignored. The present paper addresses this problem by developing a three-dimensional model which considers frosting. The model is validated with experimental data and is then used to examine the global performance of the RHE under frosting conditions. After the validation, the model will predict the impact of frost formation on the thermodynamic properties.