Energy analysis of heat pump water heaters coupled with air-based solar thermal collectors in Canada and the United States

Abstract

Heat pump water heaters (HPWHs) operate with two to three times the efficiency of electric water heaters, and over three times the efficiency of natural gas water heaters; however, this benefit is accompanied by a secondary space cooling effect that increases space heating costs. To mitigate this, HPWHs may be coupled with solar thermal collectors which preheat inlet air. The objective of this study was to compare the energy performance of HPWHs and solar-assisted HPWHs (SAHPWHs) across Canada and the United States, to determine where the SAHPWH could offset the space heating increase of HPWHs. This was done using an empirical model, with different modelling methods and assumptions that were assessed and compared. It was found that the SAHPWH could fully mitigate the space heating increase throughout winter, while decreasing the space heating load by 1–3%, and during the cooling season, decreasing the space cooling load by 7–15% in all climates studied. This research indicates that HPWHs and SAHPWHs have potential to lead a higher efficiency future, by reducing energy consumption for water heating beyond what is presently achievable with electric and natural gas storage tank water heaters.