Analysis Of The Influence Of Inter-stage Injection And Release Parameters Of R410A Two-stage Compression Heat Pump

Air source heat pump is a suitable method in the "coal-to-electricity" program of the northern clean heating project.It has the characteristics of energy saving,high efficiency,flexible installation and low cost.However,in cold areas with low temperature,there are still problems such as large pressure ratio,frosting and high exhaust temperature,which lead to serious attenuation of heating performance.In this regard,many experts have proposed many improvement schemes,among which the intermediate injection combined with two-stage compression technology can improve the low temperature performance of the air source heat pump and expand its application range.Therefore,this paper analyzes the key problems of the relationship between the intermediate pressure of two-stage compression,the volume ratio of the compressor cylinder and the coupling between the stages.A theoretical cycle of inter-stage release defrosting was constructed,and related research was carried out in combination with the influence of injection process on the release characteristics.Firstly,a general steady-state model of two-stage compression with intermediate heat exchanger structure is established.The model takes the volumetric efficiency and electrical efficiency of the compressor into account of the operating frequency,so that it can be used for the analysis of variable capacity and multiple working conditions of injection and release.At the same time,based on the geometric characteristics of the rotor compressor,the operation modes of the two compressors are divided into eight coupling processes,and then a two-stage compression dynamic coupling model which can reflect the dynamic compression process of the compressor is constructed.Finally,the two-stage compression heat pump test platform is used to verify the two system simulation methods.Secondly,through the method of simulation calculation and experimental test,the influence of injection ratio and capacity ratio on the parameters of the system is studied.The results showed that with the increase of injection ratio,intermediate pressure increases first and then stabilized,system heat and COP has slightly lower after the first rise in the change rule,and the larger the capacity ratio,the smaller the optimal injection ratio.In addition,the theoretical study on the release process found that with the increase of the release ratio,the intermediate pressure and temperature were nearly linearly reduced,and the system heat production and COP were significantly reduced.When the release ratio increased to 0.3,the system heat production and COP were respectively reduced by about 27% and 17%.Thirdly,the thermodynamic analysis of the compression process based on the release amount in the dynamic coupling model reveals that the compression process is discontinuous and does not follow a fixed variable exponent.In addition,the use of the steady-state model analyzes the inter-stage subcooling parameter(SC)and exhaust cooling parameter(SH)on the system the effects of various parameters.With the increase of the injection ratio,the changes in the size of SC and SH show a "parallelogram" change rule.The system heating capacity and the changes of COP and SC are closely related and have a positive correlation with the intermediate pressure.However,the SH value has a positive effect on the COP.The heating capacity is not sensitive to changes,and the maximum COP must appear at the position where the SC is larger and the SH is smaller.Finally,based on the promoting effect of interstage undercooling parameters on COP,the expression equation of the optimal intermediate pressure to the optimal cylinder capacity ratio was fitted,and the design value of the cylinder capacity ratio in the major cities in cold regions was found to be between 1.96 and 2.85.In addition,this paper takes Beijing outdoor state parameters of the heating season optimize the air source heat pump units.Taking into account the cylinder capacity design,inter-stage injection,release defrosting and variable frequency operation and other factors,the energy efficiency ratio SCOP of the unit heating season is 2.75.Compared with central heating,its primary energy consumption has been reduced by 21.9%,pollutants and CO2 emissions have been reduced by 22%,and the annual costs are lower than that of the municipal heating group’s large network and gas boilers.The results show that the optimized integration of this research system has great application potential in cold regions.