In 1994, we started a two-year six-site field test of a 6,000 Btu/h heat-pump water heater (HPWH) for the Electric Power Research Institute (EPRI).  In addition to collecting one-minute data on the performance of the HPWH, we collected 15-second data on hot water use in the homes and apartment houses.  This field test is reported in detail in an EPRI publication "EPRI/E-Tech Heat-Pump Water Heater Applications Research Field Test".  Several ASHRAE papers also report on the data collected in this field test.  These include:

CH-99-16-3: Hot Water Use at Coin Laundries

SF-98-31-2: Disaggregating Residential Hot Water Use-Part II

The primary objectives of the field test were to (1) determine the operating and maintenance characteristics of the HPWH, (2) compare its operating costs with those of a conventional electric water heater, and (3) uncover possible generic or site-specific operational or application problems.

In this project, the HPWH was tested at four single-family residences, a 14-unit apartment house and the laundry room of a 50-unit apartment house.  Most of the installations were not ducted, i.e., air was drawn into the HPWH from its immediate surroundings and discharged into the same space.  For one single-family residence the cool air leaving the HPWH was ducted to the neighboring kitchen.  At two single-family residences the HPWH was located in the basement and at the other two, in a utility room on the first floor of the house.

The field test had two phases, each lasting approximately one year.  In the first phase, the E-Tech WH-6 was tested at all sites.  In the second phase, the E-Tech WH-6BX was tested.   

In the first phase, the energy savings for the HPWH relative to a conventional electric resistance water heater were determined by disabling the HPWH for one week every fourth week and operating the building’s water heating system as a conventional electric resistance water heater

The HPWHs that were field tested in this project were developed by the Crispaire Corporation under sponsorship of the Electric Power Research Institute.  Two HPWH models were tested: the E-Tech WH-6 during the first year of the test and the E-Tech WH-6BX during the second year.

The annual energy savings attributed to the HPWHs was substantial at all sites.  They range from 1818 to 1948 kWh at the residential site with the lowest hot-water use to almost 7,000 kWh at the apartment building with the highest hot-water usage.

For the four sites where the HPWH’s electrical demand could be compared to that for a conventional water heater, the HPWH reduced the average electrical demand on weekdays from between 500 W to 2,000W.  The largest demand reductions occurred at the two sites that had sharp morning peaks in hot water use.