Economic and environmental analysis of ground source heat pump system according to operation methods

Abstract

A ground source heat pump (GSHP) system can achieve high energy performance than conventional air source heat pump system by using annual stable underground temperature. However, the GSHP system can occurred soil thermal imbalance when the system is used for a long-term operation. Therefore, in order to prevent soil thermal imbalance, increasing the spacing and depth of boreholes and combining GSHP system with auxiliary heat sources are used. However, these methods require large sites and high initial investment. This study proposes an intermittent operation as an alternative to minimize the imbalance by altering the GSHP system. A numerical simulation model that can simultaneously analyze mass and heat transfer in soils was used to accurately analyze the performance of the GSHP system. In addition, the economic analysis and life cycle climate performance (LCCP) were compared based on the numerical analysis results of the GSHP system. Consequently, an appropriate operation method for the system is proposed by comprehensively considering the analysis results for the performance, economics, and environmental impact of the GSHP system according to the operation method. The numerical analysis of the GSHP system showed that the intermittent operation method increased the heat exchange rate of the GSHP system by 15%, compared to the continuous operation method, and the borehole center temperature was higher by 0.8 °C when the system operation concluded. Moreover, the economic analysis results showed that the intermittent operation method could reduce the total cost by up to 18.7% (1,921 USD) compared to the continuous operation method because it can dramatically reduce the initial investment cost. However, as the result of the LCCP analysis for three months, the total emissions increased by up to 11.8% (793 kg CO2e) because the intermittent operation method has a higher energy consumption of the heat pump than the continuous operation method.