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This report details the laboratory testing of three air-source heat pump systems, focusing on low ambient temperature heating performance. The three split system heat pumps were tested under controlled steady-state
conditions with outdoor air temperature ranging from ~60°F (16°C) down to -5°F (-21°C). One typical method for heat pump installations in the United States is to couple with supplemental 2nd stage electric resistance heat. This 2nd stage is enabled to satisfy conditions when the heat pump alone cannot maintain indoor setpoint and is relied upon heavily during low outdoor temperature times. This study aims to determine the potential reduction in supplemental heat requirement offered by different heat pump technologies and to provide data and insight as to the effectiveness of air-source heat pumps in colder climates. Three types of systems were tested: 1) a standard 13 SEER (7.7 HSPF) split-system heat pump—typical of what is installed in new spec homes in the U.S. 2) A variable-speed, inverter driven compressor, split system heat pump and 3) a variable-speed heat pump specifically designed for low temperature application. The results are used with a simplified building model to approximate the potential savings of each type of system in several climates. The simulation suggest that using the low-ambient designed heat pump compared with the single-speed system may lead to heating energy savings as high as 19%, and substantial peak power draw reduction with peak reduction greater in warmer climates, and total energy savings greater in colder climates.

Citation: ASHRAE Conference Papers, Chicago IL