| The United Nations Framework Convention on Climate Change’s(UNFCCC)Paris Agreement has established a long-term temperature goal of holding global mean temperature increase well below 2?℃ and pursuing efforts to limit it to 1.5?℃ relative to preindustrial levels,which puts forward a new urgent requirement for energy saving and emission reduction.Fossil fuel consumption and greenhouse gas emissions are the direct impacts of climate change.At present,the cold chain accounts for about 1% of global carbon dioxide production,and the energy consumption and carbon emissions of the cold storage system as the end equipment account for more than 50% of the cold chain.Therefore,improving the performance of cold storage system and reducing carbon emissions are of great significance for global energy conservation and emission reduction.In this paper,a R404 A cold storage system sample consisting of a 5HP compression condensing unit and an air-cooler is test under year-round working conditions,and the feasibility of direct replacement of the non-azeotropic refrigerants R407 A and R407 F and the performance and energy-saving effect of the frequency conversion cold storage system are analyzed and evaluated.Firstly,a method for optimizing refrigerant charge was proposed.Under the working conditions of 32 ℃,25 ℃,15 ℃ and 5 ℃,the annual optimal charge ranges of R404 A,R407A and R407 F are determined,taking the performance and reliability of the unit into consideration.Based on this,the performance(EER,cooling capacity)and reliability(sub-cooling degree,super-heating degree,condensing temperature,evaporation temperature,and discharge temperature)of R404 A,R407A,and R407 F fixed frequency refrigeration systems under variable ambient temperature conditions are compared.The annual energy efficiency of R404 A,R407A and R407 F are evaluated and the feasibility of R407 A and R407 F replacement is analyzed.In order to further improve the performance and reduce energy consumption of the cold storage system,a frequency conversion cold storage system that can automatically adjust the compressor frequency with the load is designed.The effect of frequency on the performance under variable ambient temperature working conditions is investigated.Then,the performance(EER,cooling capacity)and reliability(sub-cooling degree,super-heating degree,condensing temperature,evaporation temperature)of the frequency conversion cold storage system are analyzed under variable ambient temperature conditions,and the annual energy saving effect of the frequency conversion cold storage system are evaluated.The experimental results show that the best annual refrigerant charge ranges for R404 A,R407A and R407 F are 5.77～6.18 kg,5.83～6.13 kg and 5.52～6.80 kg,respectively.Within the range of test working conditions,the cooling capacity of R407 A and R407 F units is increased by 10.7% ～ 16.7% and 15% ～ 20.7%,and the annual energy efficiency ratios of R407 A and R407 F units is increased by 7.7% and 12.1%,respectively.R407 F has more obvious performance advantages under low temperature conditions,but it needs to pay attention to the too high discharge temperature when replacing.The EER of frequency conversion cold storage system is higher at low frequencies and the performer is better at low ambient temperature conditions.The cooling capacity and EER of the frequency conversion unit are obviously higher than the fixed frequency unit,up to 11.9% and 7.7%,respectively,and the highest power saving rate is up to 44.48%.The investigation results in this paper can be applied as a valuable reference for the year-round performance investigation of non-azeotropic refrigerant replacement and refrigeration equipment of the same type. |
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