Investigation On Performance Of R32 Air Source Heat Pump System With Flash-tank

The energy shortage,environmental pollution,ozone hole and greenhouse gas emission have become a common problem.In recent years,R32 gradually shows competitive advantages with its zero ODP,low GWP,excellent thermal properties and low price.The flash-tank vapor injection technic was used to solve the problem of air source heat pump(ASHP)system in winter heating such as low efficiency,low heating capacity,and high discharge temperature of compressor.The study on improvement for the performance of heat pump with flash tank using R32 is of important theoretical significance and practical value.In this paper,the methods of improving the performance of air source heat pump system were compared and analyzed,and the technique of vapor injection by flash-tank was analyzed emphatically.The mathematical model of flash-tank vapor injection(FVI)heat pump system was set up and the computer program was established by using EES software to find out the key conditions of vapor injection technique used in ASHP system.The optimal injection pressure of FVI heat pump system was simulated under different working conditions,as well as the heating performance of the FVI heat pump system and conventional ASHP system.And then the optimal switching-point between the two systems was obtained by comparing the performance parameters.Based on the theoretical calculation results,the main equipment of the FVI heat pump system was calibrated and the experimental prototype was manufactured.The experimental heat pump system was set up in the psychrometric rooms.The dynamic heating performances of the FVI heat pump system with different injection pressure under experimental conditions which were developed according to national standard were tested and experimentally investigated.The experimental results indicated that under the condition of indoor dry-bulb temperature is 20 °C and different outdoor dry-bulb temperature,all of the injection ratio,heating capacity,and compressor power consumption increases with the increase in the relative injection pressure,and the discharge temperature of compressor decreases with the increase in the relative injection pressure.As for heating COP,as the ambient temperature is below-5 °C,the heating COP increases first and then decreases with the increase in the relative injection pressure.So there is an optimum relative injection pressure,at which the heating COP of the FVI system reaches the maximum value.And for the FVI heat pump system,the optimum relative injection pressure is observed about 1.2.The comparison between the performance parameters of the FVI heat pump system and conventional ASHP system indicated that the heating capacity and the power consumption of the FVI heat pump system under the optimum relative injection pressure are higher than these of the conventional ASHP system respectively,and the discharge temperature of compressor is lower than that of the conventional ASHP system.Under the condition of outdoor dry-bulb temperature is-10 °C,the heating capacity of FVI heat pump system increases by 14.6%,and the discharge temperature of compressor decreases 19.2 °C compared with these of conventional ASHP system.As for heating COP,at the condition of outdoor dry-bulb temperature is below-3.1 °C,the heating COP of FVI heat pump system is higher than that of the conventional ASHP system.As the ambient temperature is above-3.1 °C,the heating COP of FVI heat pump system is lower than that of the conventional ASHP system.It is concluded that the optimum switch-point between the FVI heat pump system and the conventional ASHP system is about-3.1 °C.Compared with the experimental results of the economized vapor injection(EVI)heat pump system,the heating COP of FVI heat pump system is higher.For the outdoor temperature of-10 °C,the heat COP of FVI heat pump system increased by 4.9% compared with that of EVI heat pump system.Overall,the problems of conventional ASHP system such as low efficiency,reduction of heating capacity,and high discharge temperature of compressor can be solved by using the technique of FVI,and the safely and reliably of the optimized system also are improved.Combined with the simple structure,the FVI heat pump system is the best choice for winter heating.