Research Of Vertical-Pipe Ground Source Heat Pump Constant Temperature And Humidity Air-Conditioning System

The ground source heat pump (GSHP) system, which combines the shadow geothermal and the heat pump to serve buildings with heat and cold energy, is an effective method for sustainable energy application. The application of GSHP system mainly covered in conventional buildings. However, few investigation is carried out for GSHP system applying in some buildings, which require the indoor enviroment to keep constant. The energy cost of air-conditioning is large in these buildings. Based on the special of constant temperature and humidity air-conditioning system and climate of hot summer and cold winter zone, the vertical-pipe ground source heat pump constant temperature and humidity air-conditioning system was analyzed. The main work are summarized as follow:(1) For analyzing the performance of the GSHP constant temperature and humidity air- conditioning system, the mathematical model was built.(2) The constant temperature and humidity air-conditioning system in the archives building in Shanghai covers an area of 8000m~2. The system consisted of ground heat exchanger, two heat pumps with heat recovery and AHU (air handling unit). 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. When operated in cooling mode, part of heat from condenser was used to reheat the air in AHUs, which would reduce the heat rejected to the soil.(3) The performance of the system, the heat exchange of the ground heat exchanger and soil, and the temperature distribution of soil are predicted by mathematical model of the constant temperature and humidity GSHP system. It is shown that the total heat rejected to soil is a year is 2630GJ while the heat absorbed from soil is 2114.7GJ in Shanghai. The unblance rate is 19.6%.(4) Experiments of all-year operating modes are carried out. Under the typical winter weather condition of Shanghai, the average COP was 5.2. For the typical summer weather condition, the average COP was 5.1. During the whole year, the indoor environment met the"Archives Design Code"issued by China national archives. The temperature of soil increased 0.7℃after one year operation. The contribution rate of heat recovery to the heat unbalance was 68.14%.(5) The long-term performance of the system is predicted with the mathematical mode combined the experimental data. It is shown that the soil temperature increases slower with the distance of the borehole increases, which is helpful for the system operates stably. The borehole distance and deepness are suggested to be 4m-5m and 80m-100m respectively in Shanghai. After 15 years operation, the increment of soil temperature with hear recovery was 66.98% lower than without heat recovery. After 15 years operation, the soil temperature increases 2.80℃with indoor set temperature 20℃while 1.03℃with indoor set temperature 22℃, the increment of soil temperature was reduced by 63.21%.(6) The region analysis showed that the thermal unbalance of soil could by solved by heat recovery in Beijing; Beside the hear recovery, the indoor set temperature should be increased to 22℃to solved the thermal unbalance in Chengdu; In Shenyang, the thermal unbalance could be solved by reducing the indoor set temperature to 18℃.