Heat Pump Water Heating for Multifamily Buildings in Cold Climates to Reduce the Energy Burden for Residents with Low to Moderate Incomes

Heat pump water heating (HPWH) for multifamily buildings in cold climates for residents with low to moderate incomes (i.e., residents who experience high energy cost burdens) poses several technological and initial cost-related issues. Generally, the energy burdens families face can be relieved by air-source HPWH systems, which are more efficient than other water heating systems such as electric-resistance and gas-fired technologies. However, the heat source for heat pumping is important in cold climates because the heat ultimately comes from ambient temperatures and the issue becomes severe during winter. Furthermore, the equipment and installation costs for HPWH systems are typically higher than those of gas or electric-resistance water heating systems. Incentive programs at the federal, state, and utility levels can remediate portions of this upfront cost and can significantly reduce the payback period for unitary air-source HPWHs in each apartment. Currently, state-of-the-art HPWH solutions for centralized systems exist and should be considered before retrofitting centralized HPWH solutions to unitary solutions in cold climates because of the ultimate source of heat and space constraints. This paper shows that a unitary HPWH installation in each apartment is more expensive than installing centralized HPWH equipment for cold climates. Furthermore, novel configurations of water-source HPWH systems coupled with drain heat recovery systems yield the highest system performance and thus lower the energy burden for users, compared with the performance and energy burden of air-source HPWH solutions. The elevated temperature level of the drain compared with outdoor air temperature in the winter months results in significantly higher COPs.