Experimental and numerical results on the performance of a heat pump

Abstract

A 21 kW ground source heat pump (GSHP) operating since 2013 in Alaska is described in this paper. Six years of successful operation in an extreme climate and measured performance data from 2013 to 2017 prove the viability of heat pumps for extreme cold regions. Summary of performance evaluation data such as monthly electric energy use and cost, savings of the heat pump system compared to the cost of heating oil, energy extracted from the ground, heat delivered to building are tabulated by months. The coefficient of performance (COP) of the heat pump is calculated from the experimental data, which show the COP to vary from a maximum value of 4.15 to a minimum value of 2.34 depending on the heating load of the month and the ground temperature. Cost comparison shows savings by heat pump over regular heating oil boilers of 80% efficiency. In cold regions it is of concern that GSHP can create frozen ground or permafrost around the ground heat exchanger coil by extracting too much heat from the ground. A finite element heat conduction simulation performed over the ground heat exchanger coil spanning over a 30-year period shows that small volumes of frozen ground form around the coil each season, but they melt away during the summer by the recharge of heat from the solar heat gain. The mechanical system of the heat pump, sensors for measurements and cost of the system components are presented, which would be valuable to designers implementing heat pumps in various locations of the world.