Study On Quasi-two Stage Compression High Temperature Heat Pump With Mixed Refrigeration

Research and development of high temperature heat pump can expand the scope ofapplication of heat pump technology, and gain more energy saving and environmentalbenefits. The high condensation pressure, high exhaust temperature and low COP of thecurrent heat pump limit the development of this technology. Consequently, considering boththe refrigeration and system, air source heat pump based on quasi-two stage compressionsystem with economizer, which can produce80°C hot water andfilled with mixedrefrigeration was suggested. Both theoretical and experimental investigation on refrigerationand system of high temperature heat pump were conducted.Both qualitative and quantitative analyses on environmental features (COP and GWP),safety features (toxicity and combustibility), working pressure and heating capacity ofrefrigeration were considered as the principle of selecting proper refrigeration. In thecalculation of thermal properties of R134a based on PT state equation, the error of the resultswent larger when the state went closer to the critical point, which failed to satisfy thecalculating demand of high temperature heat pump. Hence, customized designing methodand cycle performance calculation method were realized using Matlab which can invoke datafrom REFPROP. Considering the all of the indexes, three binary mixed refrigeration MA,MB and MC and were proposed. The ratio and basic features of them were determined.The system structure of quasi-two stage compression heat pump were analyzed anddetermined. The mathematical model of the compressor were constructed. For R134a,volume ratio of pre-compression of low temperature heat pump and high temperature heatpump were1.2~1.4and14~1.6respectively. How the air admission ratio change with theproduct temperature was determined. Quasi-two stage heat pumps were found to have higherheating capacity and COP comparing to the current systems. Through the theoretical study ofrefrigeration MA and MC, the comprehensive performance were found to be better when themass fraction of the first component is higher. Through the comparison of refrigeration MAand MC, MA was found to have higher heating capacity and lower COP.Prototype high temperature heat pump were made and tested in laboratory, filled withR134a and MA. And the results from the theoretical study match the experimental results.From the experiments, the maximum mass fraction of the first component in MA were90%, when considering the maximum pressure being2.8MPa in the maximum load condition.Comparing of the results from theoretical and experimental studies, the theoretical modelwere considered to be valid. However, the characters of mixed refrigeration have to be fixedby experiments.