Influence of Water Temperature and Flow Velocity on Heat Exchange Characteristics during Thermal Energy Extraction from Running Water in Shallow Irrigation Canals

Abstract

In recent years, the utilization of heat pumps that use surface water, which is included in the geothermal heat category, as a heat source has been promoted. Agricultural irrigation canals have been constructed throughout Japan, and agricultural water flowing through canals is expected to be a heat source/sink for heat pumps. In this study, experiment was conducted by installing a sheet type heat exchanger in a shallower depth irrigation canal. The heat exchange characteristics of the heat pump system, such as the quantity of heat (the amount of heat extracted in the heat exchanger) and the heat transfer coefficient (the ease of heat extraction), were evaluated. From the experimental results, it was found that the higher the water temperature in the irrigation canals, the higher the quantity of heat and Coefficient of Performance of the heat pump system (SCOP). It was shown that the heat in flowing water in an irrigation canal can be efficiently utilized by focusing on the flow velocity and water temperature when designing a heat pump system that uses the flowing water in the canals as a heat source/sink.