| It is generally believed that the use of photovoltaic power generation systems together with air conditioners or even conventional refrigerators can get a high efficiency as a whole since the cooling demand of the user side matches in time the capacity of generated electricity from the supplier side,Such a project if successfully applied in practice can reduce air pollution effectively and deliver a positive impact on the environmental issues like greenhouse gas emission,smog,etc.On the other hand,with a rapid development of micro electro mechanical system(MEMS)and micro system technology(MST),the miniaturization in both lightweight and small taken space of any mechanical components can be possibly realized.Nowadays,the miniature active refrigeration technology,led by miniature vapor compression refrigeration,is successfully applied in the fields of chip cooling and individual micro environment regulation.The advantages using a miniature refrigeration system powered by a photovoltaic cell are apparent,however,some technological problems remain to be resolved,which provides a challenge for those researchers at the same time.In this paper,a lab-scale photovoltaic driven miniature compression refrigeration system(PMCRS)with storage batteries was established.After the gauges or probes calibrations,a series of experimental tests were carried out with the local meteorological conditions,and a performance evaluation model was also proposed.Therefore,the main contents include:(1)The thermodynamic performance of the refrigeration system was evaluated according to a series of tests.The tests were conducted in four cases,i.e.different refrigerant charge amounts,different inlet temperatures of cooling water,different rotational speeds of compressor and different cooling water mass flux.The optimal operating condition was obtained through the analysis of those obtained data,that is,the refrigerant charge amount is set at 160 g,the cooling water inlet temperature is 15 °C,the cooling water flow rate is 35 g/s,the compressor speed is 6500 rpm.(2)The operation performance of the PMCRS under different weather conditions in Tianjin was tested,with the mode of batteries in pure charging and pure discharging.According to the first and second laws of thermodynamics,the performance efficiency of energy conversion and utilization was analyzed.The results show that the designed system can provide the required power for the miniature refrigeration system.The photovoltaic power generation efficiency was 12% ~ 13%,and the total energy efficiency of PMCRS decreased with the increase of the solar radiation intensity.The maximum exergy loss comes from the photovoltaic,which has an averaged exergy loss about 240 W.Then the compressor follows,which has an averaged exergy loss about 50 W.The above two account for more than 80% of the total exergy loss of the miniature refrigeration system.(3)An optimization scheme was proposed in order to reduce the energy loss and improve the system efficiency.The scheme can ensure the required cooling capacity of the design,while the load consumption is reduced by 26%,which results in a 36% reduction in overall exergy loss of miniature refrigeration system.In addition,the proposed optimum scheme can enhance the ability for continuous working in a bad climate condition.Finally,the matching calculation of photovoltaic array and battery of the system was carried out by using the method proposed in this paper for various cases with an adjustable cooling load.The relationship between the cooling load and the required panel area of the photovoltaic array and the battery capacity has been obtained,which is expected to be helpful for the future design of such a solar energy application system. |
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