Original article published February 15, 2023 | Joseph Wachunas for New Buildings Institute

Central heat pump water heaters (CHPWHs) present a tremendous opportunity to reduce the substantial energy used in water heating and can act as giant thermal batteries. They do this by using energy to heat water during times of low grid demand and storing it for later use, enabling them to limit their energy use during peak times for the electricity grid. Leading organizations in the Advanced Water Heating Initiative (AWHI)’s Commercial Working Group are showing the grid asset implications of this in the first of its kind Bayview Tower pilot project in Seattle.

Bayview Tower is a low-income public housing facility for senior citizens located in downtown Seattle. Hot water for the residents of Bayview was provided by an inefficient electric resistance water heater that used a lot of electricity to heat water. In 2019, a dream team of organizations that included Ecotope, Seattle Housing Authority, Bonneville Power Administration, Steffes, SkyCentrics, Mitsubishi, and Seattle City Light came together to retrofit the building with a CHPWH that had the potential to reduce the energy used to heat water, which accounts for about 25-35% of the average multi-family building’s energy usage, by a factor of three.

Central heat pump water heaters are different from their residential cousins in ways you would probably expect. Instead of having individual water heater tanks in every home and apartment, central systems are much larger and provide hot water to many households at once. In the case of Bayview, one system serves 100 apartments. Nationally, there have been hundreds of CHPWHs installed to date but this technology is still early in its adoption.

The central heat pump water heater installed at Bayview broke lots of new ground and is proving many important concepts which could help guide how we heat water in these upcoming crucial decades for decarbonization. First off, the CHPWH for Bayview was a packaged, skid mounted (meaning it is permanently mounted on a metal pallet) system with many components that were manufactured off-site and then delivered by crane to the building, more or less ready to plug into place. The “plug’n play” nature of this water heater meant Bayview Tower residents experienced only a couple hours of hot water downtime while a whole new water heating system was installed. The water heater was installed in the summer of 2021 and the system has now been operational for a year and half, meeting the residents’ hot water needs while saving an estimated 135,000 kilowatt hours (kWh) annually along with significantly reducing CO2 emissions and electricity bills.