Research On Applicability Of Generalized Air-Source Heat Pump In China

Frosting decreases the performance of air-source heat pump and reduces indoor thermal comfort. To solve this problem, two main approaches are studied. One is improving the accuracy of control system and the efficiency of defrosting method based on current control and defrosting technologies. The other one is developing new systems to prevent frost formation on outdoor coil surface, which is called frost-free airsource heat pump. However, people are not clear about the following questions:Where are the suitable areas that these two type of technologies should be applied to?How to evaluate the performance fairly?Which are the importance approaches to improve the system performance?This paper carried out the following studies:Firstly, the physical processes of frosting and dilution are analyzed comprehensively and the frosting and defrosting processes are regarded as two coupled heat pump cycles, which are connected with the mass balance of absorbed water. Then a performance model of the generalized air-source heat pump in a single frost/defrost cycle is developed from the law of conservation of energy and the law of conservation of mass.Secondly, the method and rationality of using 1 hour as a standard period are derived and proven. Then relations between mean wet-bulb temperature and air temperature of different buildings in different cities are given to overcome the shortcomings in current annual performance evaluation system, which can not quantitatively describe the influence of outdoor humidity on performance. A new annual performance evaluation system of the generalized air-source heat pump is proposed and analyzed by the author, which considers both air temperature and humidity, founding the base of applicability analysis.Thirdly, two lumped parameter models of reverse-cycle defrosting and frost-free air-source heat pump are developed based on current research to simulate the cooling and heating performance. Meanwhile, the cooling and heating performance of a frostfree air-source heat pump is tested. The data in recent research are presented and analyzed to validate the model.Finally, the performance comparison shows that frost-free air-source heat pump is suitable in Fuzhou, Nanning and Guangzhou. Conventional air-source heat pump is suitable in Guiyang and Kunming. The performances of conventional air-source heat pump are slightly higher in other cities in southern China. Calculation results indicate that freezing regeneration method is more efficient than distillation regeneration. The influence of false defrosting are analyzed and the performance differences among reverse-cycle defrosting, hot gas bypass defrosting and frost-free air-source heat pumps are studied.Present paper establishes the performance evaluation system of generalized airsource heat pumps, guiding the reasonable application and selection of equipment, which has both theoretical significance and practical value.