Conference Year



Heat pump water heater, dehumidification, field tests


Heat pump water heaters (HPWH) have long been recognized as a low operating cost system for producing domestic hot water.  Because of the compressor and fan noise, they are usually relegated to unconditioned and unoccupied spaces, such as garages or unheated basements. They extract energy from these spaces to heat the water, with some of this heat in the form of latent heat of condensation when the air humidity is suitably high. This dehumidification byproduct may actually be beneficial in some locations where humidity may be excessive during parts of the year where the unit is located.  Two different HPWH units were used as the primary sources of domestic hot water in an occupied house located in the central United States. An add-on HPWH attached to a standard electric water heater was used for nearly eight years while an integral HPWH unit was used for almost six years. They were located in an unheated basement garage. Air temperature, humidity, and condensate amounts were measured daily. The performance of a HPWH depends on many factors, including hot water demand, thermostat setting, as well as air temperature and humidity. While these measurements resulted from uncontrolled ambient conditions for a specific application, some useful trends related to the dehumidification benefit of two different HPWH units were developed from these long term field measurements.