Field tests of variable speed heat pumps to compare load-based and fixed-speed test and rating methods.

The improved performance of variable-speed heat pump systems has resulted in their widespread adoption globally. Heat pump rating methods such as AHRI 210/240-2023 (2020) were originally developed to characterize fixed-speed heat pump performance. Recently, load-based testing methods such as CSA EXP07:19 have been developed as a response to evidence that such fixed-speed tests don’t represent realistic performance of variable-speed systems. EXP07 laboratory test results differ significantly from AHRI 210/240 ratings, yet neither approach has been validated as representative of field performance. This paper describes a field test in which six heat pumps are installed in three unoccupied test houses in Lincoln, Nebraska (a climate with a wide range of weather conditions, with heating and cooling design temperatures of -17°C and 34°C respectively. Each house has separate ducted and ductless systems, instrumented to collect performance data; the systems alternate operation weekly. After field testing, the same units will be tested in a certified laboratory using both AHRI 210/240 and an updated load-based method, SPE-07:23 facilitating comparison between the laboratory and in-situ performance. This will allow a fair assessment of the representativeness of each rating method.