Field Assessment of Ducted and Ductless Cold Climate Air Source Heat Pumps

Abstract

Air source heat pumps (ASHPs) have become one of the most exciting options for energy and environmental advocates. With large fractions of the country relying on delivered fuels (propane, oil) and electric resistance as their primary heating source — and an ever “greener” grid that is making electricity even more attractive — cold-climate air source heat pumps are starting to deliver on the promise of energy efficiency, reduced emissions, and happy customers. 

Recent changes to the new generation of ASHPs allow heat to be transferred into homes from exterior temperatures below 0° F, which has improved the capacity and effectiveness of ASHPs for a greater portion of the cold-climate heating season, thus reducing electricity and delivered fuel use. This paper reports on the updated results from a seven-site field study of cold-climate ASHPs that were installed in Minnesota homes, along with detailed monitoring equipment, to collect data. Both ducted and ductless systems were installed and analyzed. The study included a newly available ducted unit with plenum booster that eliminates the need for flex fuel systems. 

Data analysis showed considerable cost savings for the homeowner, from 30% to 56%. For retrofits, paybacks will typically be longer than 10 years, unless equipment replacement is necessary. At either heating or cooling system failure, heat pumps paybacks drop to 5- 6 years. For the flex fuel systems, the increased COP reduced the total propane consumption by about 60%, for the majority of MN homes, which is less than 500 gallons of annual consumption. This limits the need for costly winter refueling, as 500 gallons is the typical residential storage volume.