Can ground source heat pumps perform well in Alaska?

Abstract

The long heating season and cold soils of Alaska provide a harsh testing ground for ground source heat pumps (GSHPs), even those designed and marketed for colder climates. Fairbanks, Alaska has 7,509°C heating degree-days18 (13,517°F HDD65) and only 40°C cooling degree-days18 (72°F CDD65). This large and unbalanced heating load creates a questionable environment for GSHPs. In addition, soil temperatures average around freezing (0°C/32°F); the soil may be permafrost year-round, just above freezing, or in an annual freeze-thaw cycle. In 2013 the Cold Climate Housing Research Center (CCHRC) installed a GSHP at its facility in Fairbanks. The heat pump replaced an oil-fired condensing boiler heating a 464 m2 (5,000 ft2)office space. The ground heat exchanger was installed in a marginal area underlain with permafrost near 0°C (32°F). The intent of the installation was to observe and monitor the system over a 10-year period in order to develop a better understanding of the performance of GSHPs in ground with permafrost and to help inform future design. The system enjoyed one season of better-than-expected performance, averaging a COP of 3.7its first winter. By the third winter, the COP had dropped to an annual average of 3.2 and ice had started to develop in the area around the heat extraction coils. A combination of physical monitoring and numerical modeling is used to evaluate the heat pump system.