| Simulation of refrigeration and air conditioning equipment is an important method in the design and production of modern refrigeration and air conditioning equipments. Using the simulation model to develop and optimize the products, it can reduce the number of tests, shorten the development period and save costs. Comparing with conventional air-cooling heat pump and chilling water unit, water source heat pump has obvious advantage in energy saving and it is a promising technology in the field of building energy saving. In this paper, a simulation model of water source heat pump units is established. The validity of the model is confirmed using testing. And the model is used in the engineering problems. The main research works contain the following three parts.The screw compressor, thermal expansion valve, shell–tube type condenser and flooded evaporator are simulated using the lumped parameter model. According to energy conservation and mass conservation, the system model is established. In the heat exchanger model, only the outlet enthalpy of refrigerant is assumed. And the outlet temperature of cooling water or chilled water are calculated by the conservation of energy, i.e., the conventional iteration process is not necessary in the present model. The outlet pressure of compressor can be calculated by compressor performance parameters. In the system model, only the evaporation pressure is assumed. Then, the model is optimized, the processing speed is improved. The effect of the opening degree of expansion valve is also considered in the model, which may affect the heat pump performance, and the system mass balance is controlled by the expansion valve opening.A full size performance test apparatus of water source heat pump units is build to confirm validity of model. The prediction of simulation has been compared with experimental results and a good agreement with relative error less than 5% is obtained. Furthermore, the performance test is also carried on different water quality, which leads to changes in the thermal resistance of heat exchangers. The results show that the coefficient of performance of the test unit has a less than 3.73% drop in the testing range.The climate characteristic of Chongqing is hot in summer and warm in winter. The heating load is small in winter. If the cooling load will be satisfied, the heating load can be met. So, the main study is cooling season in this paper. According to yearly temperature changes of the local Yangtze River in Chongqing, the performance of heat pump is predicted. The results showed that hourly river temperature has little effect on the coefficient of performance, and the monthly average temperature led to the coefficient of performance fell 5.01%. The model is used to calculate and analyze the variation of water source heat pump performance. The results show that the Yangtze River water as cooling source can ensure stable and reliable operation of the unit. The impact of river water temperature is mild on the unit performance. The energy saving potential, however, is remarkable. Taking an office building for example in Chongqing, the proposed model is also used to calculate the best combination of water source heat pump unit and conventional chilling water unit. The results show that for both kinds of refrigerating unit, the optimal combination isn't the combination of two same units. And the energy-saving of the river water source heat pump unit in the case project is calculated to be 13.1%. |
PDF Full Text Request