Discovering Air-to-Water Heat Pumps

Update: April 2023

Samantha Hill, CEE research engineer, presented an interim case study on this project at ASHRAE’s 2023 Cold Climate Conference in March. Through continuous power, flow, and temperature monitoring, the project team assessed the operational behavior and calculated system performance efficiencies for each AWHP system in the field study. While coefficient of performances (COPs) above 3 were observed, unaligned control logic between the outdoor compressor unit, indoor distribution unit, and thermostat can quickly reduce the COP by 50% or more. Optimizing system controls could deliver reliable comfort and efficiency gains that will be vital to leverage the remarkable flexibility AWHP systems may offer.

Overview

Recent work with heat pump technology has yielded options that are high in efficiency, but also high in cost, like ground source heat pumps (GSHPs), which require a geothermal well. An alternative heat pump technology — the air-to-water heat pump (AWHP), a new variant of an air source heat pump (ASHP) — uses electricity to move heat from outdoor air into indoor water. These systems are compatible with radiant heating, domestic hot water, and forced-air distribution. They offer the potential flexibility and higher efficiency of GSHPs at lower costs that are comparable to air source heat pumps. 

This project is a field study of AWHPs to characterize and evaluate their efficiency, performance, and cost-effectiveness. AWHP systems have the potential to play a central role in the future of residential electric heating, which is used in 17% of the homes served by Minnesota’s cooperative and municipal utilities. Field-monitored units are essential to demonstrate their promise in cold-climate applications.