In-field performance evaluation and economic analysis of residential ground source heat pumps in heating operation
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2019 Elsevier Ltd The objective of this study is to investigate the field performance, economic benefits, and environmental impact of ground source heat pumps (GSHPs) for residential space heating compared with conventional natural gas furnaces in a severely cold climate. A total of 32 residential houses with 16 vertical and 16 horizontal loop GSHPs in Iowa, U.S. were included in this study. The required heating energy in each house was estimated by using the heating degree-day (HDD) method and the building characteristics obtained during the on-site energy audits. The monthly GSHP electricity use in each house was collected over two consecutive heating seasons. Based on the estimated heating energy and the monthly GSHP electricity consumption, the coefficient of performance (COP) was derived for each unit on a monthly basis over the dominant heating period. Results showed that the median values in the calculated COP were 2.8 for both horizontal and vertical loop systems. The calculated COPs were found to be 30%124% of the nominal values for horizontal systems and 46%110% for vertical systems, with an average being 80% of the nominal value for both horizontal and vertical systems. In addition, 28 out of 32 GSHPs showed lower calculated COPs compared with the nominal values. The economic analysis showed 4486% savings in energy expenses as a result of using GSHPs in place of conventional natural gas furnaces, with median savings being 7077% depending on the electricity rates. The environmental analysis showed 23%61% CO2 emission reduction with a median of 45% compared with natural gas furnaces. These results quantified the economic and environmental benefits of using GSHPs in Iowa, U.S., which provided essential information for policy making and incentive program development. Also, the developed analytical approach to determining the field performance of GSHPs is suitable for large-scale, long-term GSHP performance evaluation given its minimum requirement on field measurements and readily available utility data.
