Operation optimization of the coaxial deep borehole heat exchanger coupled with ground source heat pump for building heating

Abstract

• The transient numerical model of the coaxial heat exchanger is established. • Operation optimization method for the heat pump system is developed. • The underground heat transfer model is validated using test data from literature. • The operation of the system before and after optimization is compared. Geothermal is considered to be one of the most promising renewable sources for district heating. Ground source heat pump systems coupled with the coaxial deep borehole heat exchanger have been widely applied because of their high efficiency. However, in order to reduce the total energy consumption of the system, there are few studies on the optimization of the water flow rates in the coaxial deep borehole heat exchanger by time to meet the load change during the heating season. In this paper, an optimization method for the two flow rates which are set at two time periods respectively every day in the coaxial deep borehole heat exchanger during the operation of the ground source heat pump system is proposed. The application of the method is to determine the applicable flow rates when the temperature of the next day is predicted. Space heating of a building (located in Tianjin, China) is taken as a scenario, comparisons were carried out on system operation before and after optimization, which shows that the method has a good effect on the energy-saving operation of the system. After optimization, the total power consumption of the system is reduced, the total performance coefficient of the equipment as well as the temperature difference between the inlet and outlet of the underground heat exchanger is increased, and the trend of flow rates changes with time is the same as the indoor and outdoor temperature difference.