The performance of an open-loop lake water heat pump system in south China

A district heating and cooling (DHC) system that utilizes lake water as heat source–sink of heat pumps has been constructed in Xiangtan, a city in Hunan province in south China. An initial analytical study had been carried out before the construction. In this paper, a simplified two-dimensional model is developed to simulate the steady lake water temperature (LWT) distribution during continuous operation. The simulation results indicate that the impacts of the discharge on entering water temperatures (EWT) and the ecological environment of lake are acceptable. Field test results showed that the COP values of the system were, respectively, 0.7–0.85 higher in cooling season and about 0.46 higher in heating season than those of the air-source heat pump (ASHP) units at the same sink and source temperatures. An acceptable payback period of 5.6 years was found through an economic analysis based on the comparison between the initial and operating costs of the system and those of the distributed ASHP units that would have been installed according to initial scheme.