A residential heat pump water heater (HPWH) of integral-type design (heat pump unit mounted directly to tank with no water circulation pump) has undergone both durability and field performance testing. Results of two rounds of durability testing and evaluation of as-installed field efficiency vs ambient conditions at HPWH location are summarized in this paper. Ten of the HPWHs were run through an initial durability test designed to represent seven to ten years of normal compressor cycling to meet hot waiter needs of a residence. The first generation control system proved to be the least reliable component of the units with a 40% failure rate for its temperature input sensors and one complete system failure. After modification of the controls a second durability test was run with five units. There were essentially no operational failures during the second test. In parallel with the durability tests, HPWH units were installed in occupied residences at 18 US locations and field performance data were collected for 1-2 years. Results for two units with differing degrees of exposure to seasonal ambient air temperature and supply water temperature variations are presented and interpreted in this paper. For the first unit, installed in a conditioned space with well water supply, such seasonal temperature variations were small. The average field-measured coefficient of performance (COP) over a 75-week test period for this unit was 2.44 ±5% and weekly averages ranged from 9% below to 10% above the overall average. For the second unit, installed in an unconditioned space with city water supply, the seasonal temperature variations were substantial. Its average COP was 1.81 ±5% over a 104-week test period and weekly averages ranged from 38% below to 28% above that value.
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