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The Effect of Alternate Defrost Strategies on the Reverse-Cycle Defrost of an Air-Source Heat Pump

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Title: The Effect of Alternate Defrost Strategies on the Reverse-Cycle Defrost of an Air-Source Heat Pump
Author: Schliesing, J. S.
Abstract: The effect of alternate defrost strategies on the transient performance of the air-source heat pump during the reverse-cycle defrost was investigated. Tests of a base-case heat pump configuration and defrost strategy were completed to provide a basis for performance evaluations of the alternate defrost strategies. The compressor and indoor coil fan operated continuously in the base-case defrost strategy, and the outdoor coil fan was stopped. Alternate defrost strategies utilized variations in fan and compressor operation during and after the defrost. Pre-starting of the outdoor coil fan prior to termination of the reverse-cycle defrost reduced pressure spikes commonly seen at defrost termination in the base-case defrost strategy. A strategy in which the compressor was stopped and the outdoor coil was allowed to drain of melted frost during the last three minutes of the defrost improved overall cyclic performance. Strategies which involved stopping of the indoor fan during defrost or delaying the start of the outdoor fan following defrost termination had a negative impact on defrost performance. A final strategy involved down-sizing of the heat pump compressor from 3.0 tons (36,000 btu/hr) capacity to 2.5 tons capacity. This alternate configuration had a comparable overall performance with the base-case while having a reduced frequency of required defrost periods.
Publisher: Energy Systems Laboratory (http://esl.tamu.edu)
Subject: Heat Pump
Defrost Strategies
URI: http://hdl.handle.net/1969.1/94832
Date: 1988-08

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