In a laboratory study of the performance of residential air-to-air heat exchangers during operation with freezing and periodic defrosts, freezing caused the temperature efficiency of a cross-flow heat exchanger to decrease at a rate ranging from 1.5 to 13.2 percentage points per hour. Much smaller rates of decrease in temperature efficiency, 0.6 to 2.0 percentage points per hour, occurred during tests with a counterflow heat exchanger. The rate of decrease in efficiency depended on the airstream temperatures and humidities and the duration of the period of freezing. The amount of time required to defrost the heat exchanger’s core was 6 to 26% of the total operating time. The average temperature efficiency for freeze-defrost cycles ranged from 48 to 64% in tests of the cross-flow exchanger and 70 to 82% in tests of the counterflow exchanger. When the frequency and duration of defrosts were nearly optimal, approximately a ten to fifteen percentage point decrease in average temperature efficiency was attributed to the freezing and required defrosts. The results suggested that the rate of performance deteriorations due to freezing can be reduced by avoiding small airflow passages that can easily be plugged with ice and by designing the exchanger so that condensed water does not drain toward the cold regions of the core. Based on this investigation, suggestions are made for future experimental studies of freezing and for improved control of freeze-protection systems.
Citation: Symposium, ASHRAE Transactions, 1985, vol. 91, pt. 1B, Chicago
Product Details
- Published:
- 1985
- Number of Pages:
- 14
- File Size:
- 1 file , 1.6 MB
- Product Code(s):
- D-CH-85-03-2
