| Nowadays,the energy crisis and environmental problems are becoming more and more serious.It is our only choice to build a resource-saving and environment-friendly society.Comparing the energy consumption about various industries or trades founds that the construction occupies a large proportion,therefore China vigorously promotes the development of new technology about energy saving and environmental protection,encouraging energy-efficient and green building.The heat pump technology has been the concern of the community,because of its high efficiency and significantly reduction in emission,but the traditional refrigerants in heat pump system R22,R134 a,R410A and R407 C not only damage the ozone layer but also produce large amounts of greenhouse gases.Finding environmental friendly alternative refrigerants with excellent performance has become the hot spot of current research.In this paper,from the environmental protection point of view,the theoretical analysis and experimental study are conducted to analyze the cycle characteristics of heat pump system with R744/R600 a natural binary mixtures.The main contents are as follows:(1)Based on the analysis of environmental,and safety performance of binary mixtures R744/R600 a,the theoretical calculation of heat pump system with different mass ratio of R744/R600 a is carried out under the nominal operating condition.The COPh of R744/R600 a system reaches its maximum 5.292,30.99% higher than the R22 system,when the mass ratio is 16/84.And its condensing pressure and exhaust temperature are 1.12 MPa and 76.64℃,respectively,lower than that of R22 system 1.31 MPa,23.22℃.(2)Experimental study on the performance of mixed refrigerant R744/R600 a is carried out on the test-bed of R22 circulating heating type air source heat pump water heater.Setting the water and air parameters according to the national standard,the experimental results of pure R600 a show that the optimum charging mass is 500 g,then the experiments of mixed refrigerant R744/R600 a about proportion are conducted around 500 g.The heating capacity about water of R744/R600 a system increases with the increase proportion about R744,but the heating performance coefficient decreases,because of growing power consumption.The heat exchanger of original machine needs to be optimized and improved,and the mixed refrigerant R744/R600 a is not suitable for direct filling into the existing R22 system.In addition,the condensing pressure and exhaust temperature of R744/R600 a system are lower,so it is more safe and stable in compressor operation.(3)Set the opening of electronic expansion valve as 190 P,200P,210 P,220P through the PID controller in the R744/R600 a system(R600a: 500 g,R744: 4%).The heating performance coefficients are 2.35,2.79,2.9 and 3.03;heating water capacities are 50.24L/h,54.58L/h,60.95L/h and 67.7L/h;power consumptions are 18108 k J,15408 k J,14652 k J and 14112 k J;the condensing pressures of last cycle are 1.18 MPa,1.19 MPa,1.22 MPa and 1.23MPa;pressure ratioes are 6.16,5.52,4.96 and 4.77;exhaust temperatures are 94.1℃,89.89℃,85.59 ℃and 83.95℃.With the increase of opening about electronic expansion valve,the refrigerant flow increases,and the system superheat decreases,and the heat transfer efficiency goes up,so the heating performance coefficient gradually rises,and the heating time required is shortened,and the exhaust temperature,pressure ratio reduce overall. |
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