Abstract
In this paper, a theoretical analysis of heat and mass transfer in a counter-flow heat exchanger used for energy recovery in air handling unit (AHU) under sub-zero operating conditions is presented. The effect of the latent heat of water vapour condensation on heat recovery efficiency was analysed. Two main frost prevention techniques (preheating and bypassing the outdoor airflow) were analysed and compared. The values of critical outdoor air temperatures and outdoor-to-return airflow heat capacity ratios were determined on the basis of parametric analysis of frosting limits for different inlet return airflow conditions. It was found out that bypass method is characterized by lower heat recovery efficiency in comparison with preheating technique for examined range of relative humidity often observed in typical buildings applications.
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