Ground Source Heat Pump Efficiency in Cold Climates

Until recently, only a few ground source heat pumps (GSHPs) have been installed in Alaska. Increasingly GSHPs are being adopted as efficient heating devices for residential and commercial buildings in Alaska; however, significant questions about their long-term efficiency in severe cold climates remain unanswered. A study of a residential-size GSHP installed in Fairbanks, Alaska began in October 2013 in order to document the long term effects of heat extraction on the ground thermal regime and any associated degradation in the efficiency of the heat pump system. Fairbanks, located in Interior Alaska, has an extremely cold climate, along with discontinuous permafrost. The ground surrounding the heat pump ground loop was thawed to a depth of approximately 30 ft (9m) at the time of the ground loop installation, which provided a narrow band for optimizing a ground loop between the zone of seasonal frost and the underlying permafrost. These are challenging conditions for the operation of a heat pump system and provide a rigorous testing environment for using GSHPs in Alaska. Depression of the soil temperatures around the ground loop is anticipated and acceptable if within design specifications. Conditions at the surface may affect the ground temperatures and ultimately the efficiency of the heat pump. This study compares three surface treatments and their effect on ground temperatures. A combination of physical monitoring and computer simulation are used to study the effects of the heat pump heat extraction and the surface treatments on the ground thermal regime. This interim report presents information on the design of the research project, predictions from the simulations, and data from November 2013 to January 2014.