Experimental And Simulative Study On Performance Of Small-sized Air Conditioning For Cool Storage

Air conditioning cold storage technology is an effective means to alleviate the peak load on electricity grids and utilize power in the off peak period.The cooling capacity generated by the unit is stored in the phase change materials(PCMs)during the night and released during the day.The use of the technology can also reduce air conditioning operating costs as well as system installed capacity.Compared to ice storage technology,more attention has been focused on PCMs in recent years since that have higher phase temperature as a cooling medium to improve the operating efficiency of the unit.The performance of air conditioning with PCMs largely depends on the operating characteristics of the refrigeration system.Therefore,this paper focuses on the study of the relationship between the charge and throttle device with the performance of a small-sized air conditioning for cool storage with PCMs based on the experimental study and simulation.Firstly,a small-sized cool storage air conditioning with PCMs working with R22 is developed.The temperature,pressure and input power are measured.The performances under ordinary air conditioning(OAC)mode and cold charging(CC)mode by refrigeration circulation at different refrigerant charge are investigated.The results show that the suction and exhaust pressure under OAC mode both increase gradually with refrigerant charge increasing,while increase at first then decrease under CC mode.At the same time,the cooling capacity and COP_a under OAC mode and the average cold storage rate and COP_s under CC mode both firstly increase and then decrease.When refrigerant charge is 1600g,the cooling capacity and COP_a reach maximum simultaneously under OAC mode.But the optimal refrigerant charge under CC mode is 1200g.With the refrigerant charge increasing from 1200g to 1600g,the cooling capacity and COP_a under OAC mode increase by 4.9%and 4.1%,respectively,while the average cold storage rate and COP_s under CC mode decrease by 1.7%and 3.2%,respectively.Then,a steady-state mathematical model of the unit's cooling system is developed,and the accuracy of the model is validated with experimental data in this paper.The maximum relative error of the outlet pressure of the evaporator and the condenser is 9.9%and 3.6%,respectively.The maximum relative error of the outlet temperature is 8.8%and 2.6%,respectively.The maximum relative error between the cooling capacity and the input power of compressor is 8.9%and 6.1%,respectively.Finally,based on the simulation,the influence of refrigerant charge on the refrigerant flow rate,input power of compressor,subcooling degree,superheat degree,cooling capacity as well as the COP of the unit are analyzed with different expansion valve opening.It is found that COP is maximal when the refrigerant charge is 1800g and the expansion valve opening is 4.The change law of the above performance parameters under different working conditions is also analyzed at the best match value.With the increase of ambient temperature,the mass flow rate and the input power of the compressor gradually increase,while the superheat degree and subcooling degree gradually decrease and the cooling capacity and COP show a rapid decrease trend.The results can provide a reference to component matching and optimized design for the small-sized air conditioning for cool storage.