Ground Source Heat Pump And Soil Accumulated Heat Transfer Effects Research

It is a trend of world development that renewable energy is gradually to replace conventional energy, and ground source heat pump (GSHP) technology, which meets buildings needs of air-conditioning, heating etc. by utilizing shallow geothermal resource, is an important means of the use of renewable energy; meanwhile, developing GSHP is also the requirement of China's energy construction adjustment. China's land area is huge, and soil formation and climate, as well as the technology measures of GSHP applications, varied significantly at different zones, therefore it is significant to investigate the effects of soil and climate conditions on the performance of GSHP system.In this paper, the performance of conventional GSHP and GSHP with auxiliary heat rejecter and heat transfer characteristics of the soil were studied with a transient modular system simulation software TRNSYS. Firstly, a water-water heat pump model, which can be run accurately in a wide range of operating conditions, was established, and the accuracy of the model was verified. Then conventional GSHP system in three climate zone for two different building types was designed and simulated, and the results showed GSHP with proper design in cold zone and hot summer and cold winter (HSCW) zone could ensure normal operation over an extended period, however the one in hot summer and warm winter (HSWW) zone was difficult to guarantee normal operation. The relation of the design entrance water temperature (EWT) of heat pump and total system energy consumption was investigated, and the result suggested that total energy consumption did not significantly reduce with decreasing the design EWT.The investigation of Hybrid GSHP system with cooling tower as auxiliary heat rejecter was performed in cool load dominant buildings, and a novel control strategy i.e. cooling tower priority was carried out and compared from some known control strategy. The result of analysis showed that hybrid GSHP in HSCW zone should be controlled by the strategy based on set temperature different and temperature, and the one in HSWW zone should be modulated by the novel control strategy. And the ratio of flow rate through borehole loop to total flow rate should correspond to the ratio of the load that borehole loop would release to total load.Finally, a multi-functional GSHP system with cooling, heating and domestic hot water was developed and analysed. The result of investigation showed that multi-functional system can significantly improve the thermal balance of the soil; compared with traditional system, energy consumption reduced 46 percent, and the saving of the present valve of life-cycle costs ranged from 7%-40% and investment payback period ranged from 5-12 years depended on economic analysis parameters.These models developed in this paper can be easily applied in practical projects, and the conclusion is of significance for proper design and energy consumption forecast of GSHP system.