Performance and viability of air source heat pumps for residential heating in cold climates

Abstract

With an ever-increasing concern for Earth’s climate, solutions to mitigate further climate change caused by greenhouse gas emissions are continuously being investigated, one of which is heating buildings using air source heat pumps (ASHP) rather than traditional fossil fuel systems such as a furnace. The benefits of heat pumps over other heating methods such as resistive heating is their ability to transfer multiple times greater heat using the same amount of electricity by utilizing the phase change of a refrigerant and different inside and outside temperatures through use of the vapor-compression cycle. This also provides an advantage over fossil fuel-based systems by operating on electric power rather than burning fuel, greatly reducing greenhouse gas emissions. While heat pumps are a superior choice for many heating needs, heat pumps suffer performance issues when outside temperatures are low. This low coefficient of performance (COP) in cold climates has limited the widespread use of heat pumps to provide heat in the winter. The first section of this thesis will review heat pump technology and research on cold climate performance, including discussions on refrigerants, environmental impacts, and the economic cost of using a heat pump. A field test in Fairbanks, Alaska was performed and collected data on heat pump performance of a commercially available (CA) R410A-based ASHP and a prototype ASHP with new technologies and R32 refrigerant. Results of these tests revealed a 53.8% increase in COP of the prototype heat pump from -30°C to -35°C compared to the CA unit with a 26.7% average increase in COP over the 0°C to -35°C range, with increases to heating output seen as well. An economic comparison of a furnace heating system compared to both heat pumps also revealed generally lower operating costs for the heat pumps, with a potential hybrid heating system resulting in cost savings of 33% to 57% for the prototype unit and 17% to 45% for the CA unit. Year-long projections were performed for Fairbanks, AK as well as Boston, MA and Fargo, ND to evaluate performance, cost, and environmental impact in regions with different weather conditions and energy costs. Across all three locations, cost savings were seen from utilizing heat pumps over a furnace, with the Fargo location being more cost effective to use a heat pump 100% of the time. An analysis on levelized cost of heating was calculated for each location to evaluate long-term costs, with a discussion at the end about possible errors in calculations and projections.