Performance of add-on-type heat pump water heaters using two different test methods

Two different makes of add-on (without tank) heat pump water heaters (HPWH) were tested. Each of the HPWH's was subjected to a series of recovery tests similar to the Department of Energy (DOE) recovery test for conventional electric water heaters. The results of the tests (recovery efficiency, standby loss, input power, storage tank capacity and energy used) were used to compute an energy factor which could be used to calculate the estimated annual operating cost of such HPWH's. The energy factor was also determined by a series of simulated use tests consisting of four equal draws totaling 64.3 gallons of hot water per day.