Effects of Evaporator Frosting on the Performance of an Air-to-Air Heat Pump

[+] Author and Article Information
J. Martínez-Frías

Centro de Ingenieria y Desarrollo Industrial, Queretaro, Mexico

S. M. Aceves

Lawrence Livermore National Laboratory, 7000 East Avenue, L-640, Livermore, CA 94551

J. Energy Resour. Technol 121(1), 60-65 (Mar 01, 1999) (6 pages) doi:10.1115/1.2795061 History: Received April 02, 1998; Revised September 19, 1998; Online November 06, 2007


This paper shows the development and use of a transient model for evaluating frost formation on a parallel-plate heat pump evaporator. A frost formation model is derived by applying the equations of conservation of mass, momentum, and energy, as well as empirical correlations, to calculate the growth and densification of the frost layer. The frost formation model is validated by comparison with experimental results. The frost formation model is then incorporated into the evaporator subroutine of an existing heat pump model to calculate performance losses due to frosting as a function of weather conditions and time of operation since the last evaporator defrost. Performance loss calculation includes the effect of air pressure drop through the evaporator and the reduction in evaporator temperature caused by the growth of the frost layer. The results show frost formation parameters and heat pump COP as a function of time and ambient conditions. It is determined that there is a range of ambient temperatures and humidities in which frosting effects are most severe, and this range is explored to calculate heat pump operating conditions. The heat pump analysis results are expected to be useful in predicting optimum defrosting conditions, and to evaluate alternative methods for defrosting.

Copyright © 1999 by The American Society of Mechanical Engineers
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