Optimization And Application Reserch Of Constant Temperature And Humidity Of Air-Conditioning System Driven By Ground Source Heat Pumps

Ground source heat pump system is based on geothermal energy as a heat source, which is both energy saving and environmentally friendly air conditioning system. Currently, ground source heat pump of air conditioning system has been widely used in schools, office buildings, residential, hospitals and other buildings, which are all comfortable air conditioning systems. But for some particular buildings, whose indoor environment needs to maintain constant temperature and humidity throughout the year, there are no ground source heat pump system. For these type buildings, the air-conditioning system should keep stability in the whole year. As a result, the energy consumption of air conditioning system is larger than other type of buildings. In this paper, Based on a constant temperature and humidity air-conditioning system driven by GSHPs in an archives building in Shanghai as a experimental platform, a large number of experimental work has been done. At the same time, we have established a theoretical model and finished much theoretical analysis. The main works are summarized as follows:1. Based on a constant temperature and humidity air-conditioning system driven by GSHPs in an archive building in Shanghai as an experimental platform. The archive building covers an area of 8000 m2. The ground heat exchanger consisted of 280 vertical boreholes with the depth of 80 m. The distance between the boreholes is 4 m. The diameter of the borehole is 160 mm. There is a single PE U-tube with the outer diameter of 32 mm in each borehole. The air conditioning system utilizes the constant temperature and humidity AHU as the terminal unit. When operated in cooling mode, part of heat from condenser is used to reheat the air, which would finish the air conditioning program and also reduce the heat rejected to the soil in summer.2. In order to analyze the performance characteristics of the constant temperature and humidity air-conditioning system driven by GSHPs, established a theoretical model. Based on the characteristics of the building load, performance of heat pump unit and heat transfer between the heat exchanger and the soil, developed a numerical analysis software. Based on the theoretical model, the theoretical analysis of the performance of the system and the soil temperature distribution has been done.3. Experimental study on the constant temperature and humidity air-conditioning system driven by GSHPs has been done. (1) Experimental study of the performance of the heat pump unit and the indoor environment in the typical day of the various seasons has been done, respectively. The experimental results show that the COP of heat pump unit can reach to 5.1 and 5.3 in summer typical day and winter typical day. At the same time, the air-conditioning system can meet the indoor environment requires, which is constant temperature and humidity. (2) The experimental results show that the heat rejected to soil deduced with the increase of the indoor temperature. So increasing the indoor temperature has great benefit to the stability of the ground source heat pump system. (3) When the system utilizes the condensing heat recovery technology, the unbalance of the soil energy reduced to 16.3%. Compared to the system without the condensing heat recovery technology, the system reduced the heat rejected to soil about 33.7%. The soil temperature increased about 0.7℃, after the system run a year.4. Based on the theoretical model and the characteristics of the experimental platform, the optimization analysis and the utilization of the system have been completed. (1) Based on the indoor design temperature, the optimization analysis has been done. According to the National Archives Building Design Code, the range of indoor design temperature is 14℃~24℃, which is the range for the optimization analysis. From the view of the system's long operation, the higher of the indoor design temperature has the benefit for the alleviation of the unbalance of the soil energy. As a result, the heat pump unit would run at a high efficiency. Considering the system's energy saving and the stability, the indoor design temperature is recommended in the range of 22℃~24℃. (2) To promote the application of constant temperature and humidity air-conditioning system driven by GSHPs, the regional analysis of the system has been done. The results show that the system can be utilized successfully in the cold areas and in the mild areas. For the cold areas, the solar or other heat source should be assisted. For the areas which are cold in winter and hot in summer, the condensing heat recovery technology can be a better solution to the imbalance of the soil energy. But for the areas which are warm in winter and hot in summer, the condensing heat recovery technology should be adopted and the auxiliary cooling tower should be needed.5.This paper focused on analysis the economic effect and the carbon emission of this constant temperature and humidity air-conditioning system driven by GSHPs. Compared to the conventional chiller plus boiler system, the GSHPs static investment payback period is 3.47 years, and the dynamic investment payback period is 3.89 years. And emission less CO2 to the atmosphere about 38.0% a year. Relative to the air-source heat pump system, the static investment payback period is 1.81 years, and the dynamic investment payback period is 1.85 years. Meanwhile, emission less CO2 to the atmosphere about 37.2% a year.