Experimental Research And Simulation Of A Two-stage Air Source Heat Pump For Residential Heating

Because of advantages of high efficiency, energy-saving and environmental protection, an air source heat pump (ASHP) for low climate is being concerned. For a two-stage heat pump with flash tank, its first level throttling device has a direct effect on its intermediate pressure, exhausted temperature and heating capacity. So it is important for throttling device that how to select an appropriate form. In this thesis, the system with thermal expansion valve and capillary as first throttling device has been studied.A thermostatic laboratory and an air-source heat pump system of two-stage cycle with flash tank have been set up in this thesis. In the thermostatic laboratory we conduct a large number of experimental tests for the heat pump system, in which the capillary or thermal expansion valve is applied as the first stage thrtolling device. We have a correct ecaluation for the performance of the system through analyzing these experimental data. At the same time, these data also provide a sufficient data sample for the simulation study.This thesis builds up a system pogram for the air-source heat pump system of two-stage cycle with flash tank, and present a simulation algorithm, in which the iteration criterion and selection of iterative variables are explained in detail. In order to balance the calculation speed and accuracy of the model, we have adopted different approaches for modeling the system components. The empirical models are used to model the compressors and throttling devices. A distributed parameter method is used to model the heat exchangers.The numerical system model is validated against experimental data, and the simulation results such as the heating capacity and COP when compared with experimental data are accurate. The average maximum error is less than 4%. It is indicated that the model can be used to predict important system parameters and provide a realistic insight into the actual behaviour of the system. The model has beed further used to study the performance of ASHP whose capillary length as the first stage throttling device is changed. The simulation results show that we should apply different lengths of capillary as the throttling device of the ASHP under different operating conditions.