UC Davis

Electrification is key to reaching decarbonization goals and curbing the impacts of climate change. Multi-function integrated heat pumps provide opportunities to reduce installation costs and space required for all-electric buildings. Multi-function heat pumps can use the compressor heat during a space cooling operation, which is otherwise wasted to the ambient through the condenser coil, to heat up water for domestic use. This project tested a multi-function heat pump that combines space cooling, dehumidification, ventilation, and domestic hot water (DHW) in a compact system (POD). Evaluation of the POD was conducted in environmental chambers simulating various indoor and outdoor conditions. Air flow and ventilation rates were calibrated, and the system was operated as per manufacturer recommendations. Performance metrics were compared across two operational modes of the POD: space cooling only and space cooling with DHW production. Operational mode decisions of the system controls impact the performance, for instance, cooling COP increases during operation with DHW heating compared to space cooling-only mode. In the combined mode, it was also observed that the cooling COP diminishes by 0.1 with every 3°F rise in tank temperature. The results indicate that a multi-function heat pump performance is not only dependent on the indoor and outdoor conditions but also on the DHW tank water temperatures. This study describes the performance of an integrated space conditioning and water heating system, while shedding light on the system metrics that would be useful to evaluate and rate such systems.