ASHRAE Journal - February 2021 - 24

TECHNICAL FEATURE

Factors Influencing
Electrical Load Shape of
Heat Pump Water Heaters
BY WALTER HUNT, P.E., MEMBER ASHRAE; EBONY MAYHORN, PH.D.; TRAVIS ASHLEY; CHERYN METZGER, P.E., MEMBER ASHRAE

Heat pump water heaters (HPWHs) continue to gain the attention of energy providers
and policy makers as an efficient alternative to traditional equipment for the residential market. While the operation of individual HPWHs has been widely studied, limited
resources exist for understanding the aggregated operation for a population of HPWHs.
This study examines the electrical load shapes of HPWHs by site characteristics, using
field data from 147 residential HPWHs in the Pacific Northwest (PNW) during 2018.
Field data consisted of HPWH power consumption in
combination with a survey of site characteristics, including the general occupancy schedule, home occupancy
count, HPWH manufacturer and location of water heater
at the home. Segmenting the data set for each site characteristic, the results examine how these factors influence
the combined electrical load shape of the HPWH population. In addition, multiple weeks of data were collected
during the regional COVID-19 stay-at-home period for a
subset of the water heaters in 2020. The stay-at-home data
demonstrate how HPWH electrical demand may evolve as
employees and students increasingly operate from home.

Background
Diversified end-use electrical load profiles are important for utilities, demand response aggregators and
regional planners (for establishing baseline behavior

to design and evaluate demand-side management programs, load forecasting to make better decisions regarding generation and load resource acquisition and transmission upgrades). Until a recent study was finalized
in 2012,1 the load shape profiles produced in the early
1990s by the End-Use Load and Consumer Assessment
Program2 were heavily used in the PNW. With end-use
behavior and energy use regularly evolving, end-use
load shapes should continue to be examined.
The results presented in this article focus on electrical
load shapes of HPWHs for households in the PNW. Water
heaters make up 14% of annual household energy consumption nationally, making them the second-largest
energy use in the residential sector.3 HPWHs have the
potential to reduce the annual energy consumption of
residential water heating by 60% when compared to
electric resistance water heaters.4 Energy providers and

Walter Hunt, P.E., is a senior research engineer, Ebony Mayhorn, Ph.D., is a research engineer, Travis Ashley is a computer scientist, and Cheryn Metzger, P.E., is a senior engineer
at the Pacific Northwest National Laboratory (PNNL) in Richland, Wash.
24

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ASHRAE Journal - February 2021

Table of Contents for the Digital Edition of ASHRAE Journal - February 2021

Contents
ASHRAE Journal - February 2021 - Intro
ASHRAE Journal - February 2021 - Cover1
ASHRAE Journal - February 2021 - Cover2
ASHRAE Journal - February 2021 - 1
ASHRAE Journal - February 2021 - Contents
ASHRAE Journal - February 2021 - 3
ASHRAE Journal - February 2021 - 4
ASHRAE Journal - February 2021 - 5
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ASHRAE Journal - February 2021 - Cover3
ASHRAE Journal - February 2021 - Cover4
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