| Energy shortage has become a serious world-wide issue owing to the fast social and economic development.Recently,the extensive use of heating,ventilation and air conditioning(HVAC)systems contribute 50% of building consumption,which causes the rapid growth of building consumption.Because subcooling gives rise to the gradually approach from isenthalpic throttling process to the isentropic one,the application of subcooling in traditional vapour compression chiller will decrease remarkable energy consumption.Although the influence of subcooling degree and its thermoeconomic optimization are studied in the open literature,the quantitative conversion characteristic from subcooling power to increase of cooling capacity has not yet been analyzed comprehensively and deeply.Additionally,it is easily misleading that the amount of enhanced cooling capacity equals to the subcooling power because the variation of specific enthalpy in the subcooler is identical to the specific enthalpy increase of evaporator caused by the subcooling on pressure-enthalpy diagram.Actual,it was found that the subcooling power can not be completely converted to the rise of cooling capacity owing to the change of condenser temperature and evaporator temperature.Therefore,this paper contributes to the understanding of the thermodynamic relationship of the subcooling power and increase of cooling capacity.The parameter RICOSP,defined as the ratio of the rise in the cooling output to the subcooling power,is employed as the critical indicator and its expression is derived.A vapour compression chiller with subcooling is simulated to analyze RICOSP under different working conditions.Additionally,systematic experiment of subcooling power and growth of cooling output under two working mode of electronic expansion valve(EEV),i.e.,fixed opening and constant superheating,are considered.It is found that the subcooling results in different variation of main thermodynamic parameters under two working mode of EEV in vapour compression chiller.For the fixed opening mode,the increased evaporator temperature,decreased superheating degree and increased suction density corporately leads to the remarkably increase of refrigerant flow ratein the subcooling case.Therefore,the enhanced cooling capacity obviously surpasses the input subcooling power,the corresponding RICOSP is 1.8 to 2.0.For the constant superheating mode,due to the drop of refrigerant flow rate brought by decreased suction density and evaporator temperature(superheating degree is constant),the enhancement of cooling capacity is lower and nearly equals to the subcooling power,the corresponding RICOSP is 0.8-1.2.The theoretical analysis based on assumptions of saturated state at condenser and evaporator outlet shows that,RICOSP increased by 22.5%,17.4% and 8% as the subcooling power,chilled water flow rate and cooling water flow rate decreased by80%,respectively.Moreover,RICOSP was insensitive to the inlet temperatures of cooling water and chilled water.For the fixed opening mode at 112 pulse,it is obtained from the experimental results that the RICOSP grows by 7.5% and 3.6% with the 40% enhancement of compressor speed and 85.2% rise of flow rate of chilled water,respectively.And the RICOSP comes up by 8% when the subcooling power reduces by 26.5%.For the constant superheating mode at 10 oC,the RICOSP goes up by 32.4% and 50.1% as the subcooling power and chilled water flow rate increases by 58.7% and 85.2%,respectively.Besides,it enhances by 25.7%with 28.5% drop of compressor speed.The paper is helpful to deepen the comprehensive understanding of thermodynamic characteristic of refrigeration system as well as the quantitative conversion relationship between subcooling power and the enhancement of cooling capacity. |
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