Measured Performance Of Ducted And Space-Coupled Heat Pump Water Heaters In A Cooling Dominated Climate

Secondary Author(s)

Martin, Eric; Parker, Danny; Sutherland, Karen

Report Number




Water Heating; Buildings


Electric resistance storage water heaters were replaced with heat pump water heaters (HPWH) in eight Central Florida homes in 2013. Comparison of one year pre and post-retrofit hot water energy showed 68.5% (5.3 kWh/day) sub-metered savings. Beyond heating water efficiently, HPWH create cool air as a byproduct, which could be used to supplement space cooling. However, common practice in Florida is to locate water heaters in attached garages.

A lab test was undertaken to investigate the effect of coupling a garage located HPWH to the conditioned space with ductwork. With the HPWH ducted to and from the interior, cooling energy dropped by 3.5% or 0.8 kWh/day. Effect on space heating energy for this configuration could not be determined. Experiments also investigated using an outdoor air source for the HPWH, to supplement ventilation. During the cooling season, the HPWH tempered the outdoor air with only a minimal impact on cooling energy. Space heating energy increased by 17.5% or 1.4 kWh/d. The space coupling of the HPWH had a minimal impact on water heating efficiency.

In later field evaluation, eight occupied homes were retrofitted with a HPWH coupled to the conditioned space. Two configurations were evaluated: interior location (3 homes) and garage with ducting to and from conditioned space (5 homes). Results were more pronounced than the lab evaluation: cooling energy savings averaged 8% (1.1 kWh/day). Space heating energy use increased by 24.1%, although with considerable variation.

The cost of coupling the garage located HPWH to the conditioned space was $620. Average cooling savings for ducted sites was $49/year, for a 12.6 year simple payback. However, the space heating energy penalty cut savings by one third. This penalty could be largely eliminated in winter with a damper system to divert cold exhaust air from the conditioned space.

Date Published



Presented at the 2016 ACEEE Summer Study on Energy Efficiency in Buildings

© 2016 American Council for an Energy Efficient Economy (ACEEE)

Local Subjects

Buildings; Water Heating


FSEC Energy Research Center® Collection



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