Measured Effect of Air Flow and Refrigerant Charge on Heat Pump Performance in Heating Mode

Erin Kruse and Larry Palmiter, Ecotope, Inc.

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Abstract

In recent years there has been increased interest in the impacts of refrigerant charge and indoor coil airflow on heat pump performance in heating mode in the Pacific Northwest. The published literature contains almost no studies of this nature. As a first step to remedy this problem, extensive laboratory measurements were made on one heat pump model at Herrick Laboratories at Purdue University. The heat pump tested was a 3-ton "economy model" with a rated Seasonal Energy Efficiency Ratio (SEER) of 10 and a Heating Seasonal Performance Factor (HSPF) of 7.2, which may be representative of the heat pumps commonly found in existing homes. The measurements included capacity, power, airflow, refrigerant mass flow rate, and coefficient of performance. At each of three outdoor temperatures (17°F, 35°F, and 47°F), tests were done at refrigerant charges and airflows varying independently from approximately 30% above to 30% below the manufacturer's nominal recommended values. In addition, cycling and defrost tests were also performed to allow estimation of the HSPF. A complete set of tests was performed for each of two metering devices: a short-tube orifice and a thermostatic expansion valve. This paper summarizes the results of the laboratory tests and the HSPF values calculated for several climate zones using Air-Conditioning and Refrigeration Institute (ARI) Standard 210/240.