HVAC Heat Pump Upgrades and their Impact on Household Maximum Power Demand

Millions of US households will undergo electrification of space heating using heat pump technologies in
the coming decades. It is critical to understand how these new loads will impact household maximum
electricity demand. Past work on this topic has addressed the upstream distribution system and has
generally relied upon modeling of loads. These efforts have largely ignored the household electrical
infrastructure behind the meter and have rarely used empirical metered data. This study used metered
electricity use from several data sources representing thousands of existing US dwellings to characterize
the changes in household maximum electrical demand associated with the installation of HVAC heat
pumps in existing dwellings. Sub-metered data in 957 dwellings was used to estimate the impacts of heat
pumps on maximum demand. Smart meter data for 9,093 Vermont dwellings that installed cold climate
heat pumps was used to directly observe the change in maximum demand pre- and post- heat pump
installation. The results show that heat pumps generally add less than their rated electrical demand to
household maximum demand, but that in small minorities of homes, heat pumps add close to 100% of
their rated electrical demand. We evaluate current and proposed heat pump demand factors (100% and
50%) for use in NEC service load calculations, and we show that using typical values for demand factors
produces adequate load calculations, and that heat pumps do not need to be treated using overly
conservative values currently assumed in the electrical code.