A Semi-Empirical Method to Estimate Enthalpy Exchanger Performance and a Comparison of Alternative Frost Control Strategies

This paper describes a new method to predict the steady-state performance of enthalpy exchangers. The approach is based on the familiar ∊-NTU heat exchanger methodology and requires only two reference operating points for calibration. The reference data are the sensible and latent effectiveness for two different balanced flow operating conditions. Using this information, the method allows prediction of the sensible and latent effectiveness for enthalpy exchangers operating under any balanced or imbalanced airflow condition. The method is validated using both experimental and published catalog data from various manufacturers of enthalpy exchangers. Predicted effectiveness agrees within 5% of experimental data for unbalanced and 2.5% for balanced flow. The enthalpy exchanger model is used to compare the performance of five frost control methods for energy recovery ventilation systems. The frost threshold temperatures for different operating conditions and system effectivenesses are investigated. The comparison shows that intake air preheat requires the least additional energy and results in the smallest equipment size, while bypass control is significantly less efficient. Wheel speed control and system shutdown are the least efficient frost control strategies.