EXPERIMENTAL ANALYTICAL INVESTIGATION ON SURFACE WATER HEAT EXCHANGER OF GROUND SOURCE HEAT PUMP

摘要

A close loop surface water heat pump system is being widely used due to its high efficiency heat transfer performance, energy saving and low operation cost and environmental protection features. With reference to a surface water heat pump project servicing 40,000 m{sup}2 building area, this study focused on developing the surface water heat exchanger technology. Three types of prototype heat exchanger were designed, namely a U coil, a helical coil, and a slinky coil. Each heat exchanger was designed with 200m long 32mm OD HDPE pipe. Those three types of heat exchangers were installed in a lake one meter below the water surface. A test rig was employed to examine the corresponding summer time heat sinking performance and winter time heat sourcing performance for those heat exchangers. This paper shows the detailed study on summer time heat sinking test and modeling for those heat exchangers. The on site tests were carried out in August and September 2006, with circulation water inlet temperature of 35°C and flow velocity of 0.6 m/s. Based on the data collected from the on site test it was found that the heat transfer rates were 59 W/m, 53 W/m, and 50 W/m for the U coil, the helical coil and the slinky coil heat exchangers, respectively. Detailed analysis of heat transfer mechanisms for those heat exchangers was also discussed. It is concluded from this study that these three types of surface water heat exchangers can be applied according to their different features. U coil heat exchanger could offer higher heat transfer efficiency than others if abundant amount of surface water source is available. However the helical and the slinky heat exchangers can be a good solution for the situation of limited water source or with a deep surface water source.