Research & Programs
Heat pump water heaters have a checkered reputation in multifamily buildings due to space constraints, noise, and comfort concerns. But a new study by SWA found that when integrated heat pump water heaters (iHPWHs) are designed and installed correctly, they can operate efficiently with virtually no resident complaints.
For a project funded by the U.S. Department of Energy Building Technologies Office, Steven Winter Associates (SWA) monitored the performance of nine integrated heat pump water heaters installed in new apartments at a senior living community in southeastern Pennsylvania.
Many multifamily heat pump water heater problems stem from poor design rather than the technology itself.
Integrated heat pump water heaters need a sufficient volume of warm air to operate efficiently. They also produce some noise and discharge cool air. In single family homes with garages or basements, these characteristics are often easy to manage. In apartments, however, space limitations mean that improper equipment placement can create comfort and performance issues.
In this project, water heaters were installed in enclosed mechanical closets, but the intake air and discharge air were both ducted. The cool discharge air was directed to locations where it would not affect occupant comfort.
The result: building maintenance reported no complaints related to noise, cold air, or hot water availability.
While these findings are encouraging, they may not apply to every building. The apartments in this study were relatively large (1,000+ square feet) and specifically designed to accommodate the equipment and ductwork. Achieving similar results in smaller apartments, poorly ventilated spaces, or retrofit projects likely requires different design approaches.
Because SWA has historically seen more unsuccessful multifamily installations than successful ones, we developed the Heat Pump Water Heater Guidelines for Multifamily Buildings to help project teams avoid common design pitfalls. Download a copy here.
Across eight properly functioning units, average annual electricity consumption for water heating was 508 kWh per apartment.
Based on measured performance, SWA estimates the systems reduced water heating electricity use by approximately 500 kWh annually compared to conventional electric resistance water heaters.
As shown in the chart below, one water heater (Apartment 9) operated only in resistance mode because of an equipment issue. That unit used substantially more energy than neighboring apartments, highlighting the importance of commissioning and ongoing maintenance. Building maintenance attempted to repair the unit, but it was only running in resistance for the duration of the study.
While heat pump water heaters are more complex than conventional resistance tanks, the energy savings can be significant when systems operate as intended.
Because integrated heat pump water heaters extract heat from indoor air, they affect apartment heating and cooling loads. In the summer, cold air from the heat pump water heaters offsets air conditioning energy, but in the winter, space heating must compensate for the air cooled by the water heater.
SWA measured airflow, temperature, humidity, and HVAC performance to quantify those interactions.
Across the eight monitored apartments with working heat pump water heaters, integrated heat pump water heater operation resulted in:
Compared to the estimated 500 kWh annual water heating savings, the HVAC penalty of 73 kWh per year represented only about 15% or one-seventh of the total benefit.
In winter, heat removed by the integrated heat pump water heaters accounted for roughly 2% of total space heating energy. In summer, the cool discharge air provided a modest amount of “free cooling.”
With thoughtful airflow design and equipment placement, integrated heat pump water heaters can work well in multifamily apartments.
In this study, they delivered substantial energy savings, generated virtually no resident complaints, and produced only modest impacts on space-conditioning energy use.
SWA prepared this study for the Building Technologies Office, Office of Critical Minerals and Energy Innovation within the U.S. Department of Energy. We will post the final report when it becomes available. In the meantime, please contact us with any questions.
Click here to download a PDF version of this research summary.
