As we continue to electrify space- and water-heating, the electricity demand profile of many
buildings will change significantly, and periods of high electricity demand will likely not align
with renewable energy generation. We expect electricity demands will increase substantially
in the winter, annual maximum electricity demands will increase, and more regions will
experience annual peak electrical demands – and higher wholesale electricity prices – in the
winter. This is especially important for cold climates where 60% of site energy use in buildings
is for heating, and where heat pumps perform least efficiently. This paper focuses on one
promising solution among the many paths to electrification: the use of phase change materials
(PCM) for compact low-cost thermal energy storage (TES). We present the design and
simulation of a combi heat pump and phase change thermal storage system used for space- and
water-heating in a multifamily residence in a cold climate. To assess the benefits of this
technology, we compare its annual performance to that of a current state-of-the-art air-to-air
heat pump and separate heat pump water heater. Simulation results for IECC Climate Zone 6A
reveal that the combi heat pump with phase change thermal storage can reduce the design size
for heat pumps by 40-60%, reduce maximum electric demand by 30-50%, reduce electricity
use during 4-12-hour load shed periods by 50%, and avoid the need for auxiliary electric
resistance for both space- and water-heating. Tariff structures are highly varied between
different utilities and currently reflect higher wholesale market prices for electricity during
summer days. Consequently, although this system design provides large electric demand
reductions during hypothetical 4-12-hour load shed periods, it does not provide energy cost
reductions with current winter residential time-of-use tariffs.