Heat Pump Water Heaters

Abstract 

Heat pump water heaters (HPWHs) take heat out of the air surrounding the unit and transfer it to water stored in its tank to be used for domestic hot water (DHW). The heat is transferred through a reverse refrigeration process. Because electricity is used to transfer heat instead of generate it, as done in a traditional electric resistance water heater, energy consumption can be substantially reduced. In recent years HPWHs have begun a resurgence into the residential water heating market. HPWHs were added to the U.S. Environmental Protection Agency ENERGY STAR® in 2008 and several major manufacturers have since developed models for the US residential market.

There are several climate-specific issues that may affect performance and energy savings in Minnesota’s heating-dominated climate: the type of space heating, the presence of air conditioning, and whether the installation location is actively or passively conditioned or completely unconditioned. These items will all affect water heating energy consumption as well as net whole house energy consumption when using a HPWH.