Quantitative evaluation of environmental influence of heat emission from lake water heat pump

Abstract

In the context of global warming and the energy crisis, Lake Water Heat Pumps (LWHP) show significant advantages in sustainable energy but raise concerns about thermal pollution affecting aquatic ecosystems and system efficiency. This study uses China's Environmental Quality Standards for Surface Water to establish thermal balance through the water surface temperature method. It examines LWHP discharge impacts on lake water temperature and defines a thermal pollution rate based on the lake's thermal load capacity. Using the Nanjing LWHP project as a case study, lake water temperature was measured, and thermal load capacity was analyzed to calculate thermal pollution rates for the coldest and hottest weeks. Results show a vertical temperature gradient in the lake affects refrigerant cooling efficiency and COP variation. The thermal load capacity of the lake is higher in winter than in summer. During the hottest week, the maximum thermal pollution rate for the Nanjing LWHP system is 0.58, and during the coldest week, it is 0.38, neither causing thermal pollution. This study is significant for the rational use of LWHP systems, aquatic ecosystem protection, and sustainable energy technology advancement.