Performance Study On Ice Thermal Storage Air-conditioning System Directly Driven By Distributed Photovoltaic Under Control Strategy

Battery banks are used as a buffer and storage unit for solar photovoltaic(PV)air-conditioner,which is necessary for storing solar energy and providing cooling stably.However,there are shortcomings:the high capital cost,short life and high maintenance cost,environmental pollution,hard to recycle and so on.To eliminate the battery bank completely and,meanwhile,solve the influence for the stability and reliability of system operation because the influence of intermittent irradiation,in this paper,an ice thermal storage air-conditioning system directly driven by distributed PV under control strategy without a battery is proposed.The impedance matching dynamic model was developed to analyze the dynamic impedance matching relationship for the PV-to-compressor system under various irradiance levels.Meanwhile,the key components were optimized and the experimental study was conducted.The main research work includes the following aspects.(1)The impedance dynamic matching model of the PV array(source)and compressor(load)in PV-to-compressor system was established theoretically.The test platform has been constructed and the accuracy of the model was verified by experiments.In the typical sunny and cloudy weather conditions,the average absolute error and relative error of impedance dynamic matching were 28.5?,9.7%,16.0?and 8.2%respectively.The average SSE,MRPE,and RMSE of the typical sunny and cloudy weather conditions were 6.92,8.94%and 11.55%,respectively.The error of engineering model is small.(2)The control system of PV-to-compressor system was designed and constructed,and the performance was tested.The minimum instantaneous irradiance of system operation with the controller was 143 W/m~2 and reduced 63.7%relative to the uncontrolled case.The photoelectric conversion efficiency,the consumption of the compressor,the operating rate of the compressor,and the quantity of ice and COP were improved by 83.7%,79.9%,58.1%,81.9%and 60.4%,respectively.Finally,the quantity of ice was 196.8kg and COP reached 0.263 with the controller.In addition,the inverter efficiencies of the control system with the nMPPT controller were 51.22%and 96.24%for the ordinary compressor and variable speed compressor,corresponding to an improvement of 87.90%for the latter.For the control system of PV-to-system,variable speed compressor is more suitable for intermittent photovoltaic energy.(3)The experiments with different PV array capacities and evaporator size were performed;meanwhile,the PV array and evaporator were optimized to improve the heat transfer performance of evaporators.The COP of system reached 0.284 when the PV capacity was 2.28 kW,which was an improvement of 39.2%compared with when the PV capacity was 3.04 kW,but the OSR decreased 47.2%.The mass of the ice and EER of the double coil tube evaporator were improved by 62.0%and 52.1%,respectively,relative to the single coil tube evaporator under nearly the same daily total irradiance.The influence of supercooled evaporator temperature was greatly improved.(4)To explore the influence on the system of different daily cumulative total irradiance values and different cooling energy use models,the experiments were carried out.The COP of system reached 0.289 under an optimal irradiance of 16.8MJ/m~2.The OSR increased with increasing daily cumulative total irradiance,and the OSR reached 0.852 when the daily cumulative total irradiance was 22.4 MJ/m~2.The refrigeration EER improved by 28.9%,the COP of system improved by 25.4%and the cooling time increased 59.2%with model A1 compared to the model A3.Finally,the highest COP of the cooling system reached 0.362 when the cooling energy using model was B1.