Performance evaluation of ground source heat pump using direct expansion method

Abstract

This paper describes the experimental results and the performance of ground source heat pump using the direct expansion method. Ground source has potential energy, which does not come from the earth center, but from the sun, at local places. This kind of energy is clean and does not affect the environment. The underground temperatures are more stable than air temperature. The temperature beneath the about 10 m from the surface maintains a nearly constant temperature about 15-20°C. Ground Source Heat Pump (GSHP) absorbs energy from the earth by applying this constant temperature. Authors paid attention to shallower depth than 100 m under the ground surface. In order to obtain the basic data, authors tried to experiment on GSHP based on direct expansion. In this experiment, performance evaluation was carried out during 48 hours operation. The performance of the ground sources heat pump system was evaluated by coefficient of performance (COP), which is determined by the ratio of heat exchange rate to consumption power of the compressor. The COP approached to 12.3 in cooling mode and 4.2 in heating mode. Totally, COP of GSHP with direct expansion method is higher than that in air-source type heat exchanger or indirect heat exchange method. In addition, long term test operations have to be considered for practical application in the near future.