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Performance of residential air-to-air heat exchangers during operation with freezing and periodic defrosts

Conference ·
OSTI ID:5985992
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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 10 to 15 percentage point decrease in average temperature efficiency was attributed to the freezing and required defrosts. The results suggested that the rate of performance deterioration 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. 1 reference, 8 figures, 2 tables.
Research Organization:
Lawrence Berkeley Lab., CA (USA)
DOE Contract Number:
AC03-76SF00098
OSTI ID:
5985992
Report Number(s):
LBL-18024; EEB-Vent-84-21; CONF-850123-1; ON: DE85008675
Country of Publication:
United States
Language:
English

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Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
320101* -- Energy Conservation
Consumption
& Utilization-- Residential Buildings-- (-1987)
42 ENGINEERING
420400 -- Engineering-- Heat Transfer & Fluid Flow
BUILDINGS
COUNTERFLOW SYSTEMS
CROSSFLOW SYSTEMS
DEFROSTING
DESIGN
EFFICIENCY
FREEZE PROTECTION
FREEZING
HEAT EXCHANGERS
HUMIDITY
RESIDENTIAL BUILDINGS
VENTILATION