Character Analysis And The Program Design Of Ground-source Heat Pump System

With the increasingly expense of energy by human beings, the impact of energy to the human economic, social, resource and environmental becomes more and more obvious. Energy reduction has become the focus of all countries concerned. Ground-source heat pump technology has been caught more and more attention due to its significant energy saving and environmental protection features.According to a ground-source heat pump project of a office building in Shanghai, this paper introduced and analyzed the design and performance of this project. Based on the building load calculated by the DEST simulation software, two programs were compared. One just uses the ground-source heat pump, another makes use of a ground-source heat pump and an air-cooled chiller as an auxiliary cooling equipment. Taking the system's initial investment into account, we chose the composite ground-source heat pump program.In this project, the Pt100A level PRTs were attached in the pipe wall in order to test the temperature changing. The paper analyzed the heat exchanger performance according to the temperature data in a operation cycle from may 2007 to may 2008. The ground-source heat pump system was operating intermittently because of the characteristic of the heat load in the office building. In the summer, the temperature fluctuated. And when the building load became bigger, so is the extent of the fluctuations. As the running of the system, the average soil temperature increased. The average maximum temperature reached 29.5℃, the largest capacity of single-hole reached 53W / m. In winter, the temperature fluctuated as well. As the operation of the system, the average soil temperature reduced. The average minimum temperature drop to 11.9℃, the largest capacity of single-hole fell to 37W/m. The system was running well, it met the design requirements. However, because the constant water system, it often appeared that"big flow but small temperature difference"in the early and end of the cooling season as well as heating season, the author suggests that it be changed into variable water system. For the system usually runs in partial load, the rotatable operation of heat exchanger was been proposed. In this rotatable operation, it can extend the time for the resumption of the soil and ease the change of the soil temperature.In this paper, the author developed a ground-source heat pump system and simulation program according to the Technical code for ground-source heat pump system and one-dimensional line-source model. The program achieved the function of the length design of the heat exchanger under the ground, simulation of the soil temperature and the water temperature in and out of the exchanger. And it also can calculate the system energy consumption by referring to the heat pump unit consumption, water pump consumption, and auxiliary cooling system consumption. When we put the parameters of the office building project into the program, the calculate result well matches the measured data. At the same time, we put forward to further improvement of the process according to the actual application of this program.By studying on factors effect on the performance of underground heat exchanger by the program, the results indicated that the thermal properties of soil and the backfill material have the largest impact on the performance of the system. We should increase the heat conductivity of the soil and the backfill material to reduce the energy consumption. Increasing the soil moisture content by watering the soil can reduce the rise of the soil temperature and energy consumption effectively. The heat conductivity of the backfill material with the conductivity of 2.0W/m℃is economical. When studying the influence factor of the heat short-circuit in drill, it showed that wrap insulation on the out water pipes is the most effective measures to reduce the negative impact of the heat short-circuit.In the end, the paper analyzed the rotatable operation of heat exchanger. It found that this operation can alleviate the negative impact of soil temperature rise because of the long time running of the system. And when rotate more frequently, the smaller the change of the siol temperature. Particular for some project usually running in partial load for a long time, using the rotatable operation of heat exchanger is an effective way to improve system performance.