Study On The Dynamic Characteristics Of Air-Source Heat Pump Units

Air-source heat pump (ASHP) has many unique advantages, such as high efficiency, convenient operation and no pollution to applying areas etc., so has been broadly used in china, especially in central south area and lack-of-water area. But the frost, which is accumulated on the evaporator for certain surrounding conditions, can degrade the performance of ASHP and the periodical defrost is necessitated.On the basis of simulation and experiment, the dynamic characteristic of frosting and defrosting of ASHP is studied. A set of simple equations is put forward to model the reverse cycle procedure of defrost and is put into the practice to simulate the dynamic characteristics of frosting and defrosting of ASHP. The good comparisons between simulations and experiments show that the system simulation model is valid in the research on the dynamic characteristics of ASHP and the mentioned method of calculation is available in the simulation.For the reason that the defrost methods of ASHP can not satisfied the need of owners, a novel adaptive defrost method is brought forward, which is grounded on the modern modeling techniques and the change rate of tube-fine temperatures. The method integrates the surrounding conditions and the response of the ASHP during operation. Simulating results show that the novel defrost method can be adaptive depending on the surrounding conditions and the situation of ASHP, so is a guideline to the intelligent defrost of ASHP.To expand the usage of the system models, the dynamic characteristics between the HFC refrigerant and HCFC refrigerant in the existing system is simulated. The comparison shows that R407C refrigerant is available in the existing equipment, but has lower coefficient of performance.To improve the performance of ASHP, an improved ASHP system is presented. Different from the original system, the new one can control the refrigerant flow rate bythe sub-cooling of condenser and adjust the sup-heating of the compressor inlet vapor by the heater in accumulator. The simulation shows the new system not only has better dynamic characteristic of frost and defrost of ASHP, but also has higher coefficient of performance. The system can be used in the R&D of manufacture.The future research on the frost and defrost of ASHP is prospected at last.