This report documents the performance of a heat pump water heater (HPWH) utilizing
carbon dioxide (CO2) as the working refrigerant. The unit was installed in a Redding,
California all-electric Zero Net Energy home and monitored in detail over the course of a
year. The unit offers advantages over conventional HPWHs in that the efficiency is higher,
the water heating capacity is higher, the heating output is stable over a much wider range
of outdoor temperatures, there is no supplemental electric backup heating, and the CO2
refrigerant has a global warming potential of 1.
Original Publication Date: April 8, 2019
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