Thermodynamic Evaluation for Intermediate Temperature Optimization in Low Temperature Heat Source Cascade Heat Pump Technology

Ali Hussain Tarrad

Abstract


A thermodynamic analysis assessment for the intermediate temperature in the cascade heat exchanger of a Cascade system is outlined. R407C/R134a and R410A/R134a pairs are studied at low evaporating temperature range between (-10 and -2) °C and (70) °C and (75) °C high temperature condenser levels. Low temperature heat sources are considered as the external driving potential sources and brines as thermal fluid carriers of energy. The analysis was based on a target temperature of hot water at the range of (60-70) °C out of the heat pump. Cascade heat exchanger intermediate temperature range of (28.5 to 39) °C was studied. The high extreme intermediate temperature exhibited the best heating COP for both refrigerant systems regardless of LT evaporator or HT condenser temperatures. The minimum isentropic efficiency of commercially available compressors was used in this investigation, a value of (70 %) was chosen. R407C/R134a system achieved only (1 %) higher COP than that of R410A/R134a for the whole test range of intermediate, LT evaporator, and HT condenser temperatures. The results showed that the heat pump heating COP at LT evaporator of (-7) °C and HT condenser temperature of (70) °C showed similar characteristic values to that of LT evaporator (-2) and HT condenser of (75) °C for intermediate temperature range between (31-39) °C. The highest COP was achieved at (-2) LT evaporator temperature and (70) °C HT condenser temperature. It was ranged between (2.2) and (2.8) for the whole test range of intermediated temperature. The lowest heating COP was experienced when the LT cycle refrigerant evaporates at (-10) °C and the HT cycle refrigerant condenses at (75) °C for both refrigerant pair systems. It was ranged between (1.95) and (2.4) at (28.5 to 39) °C intermediate temperature. Increasing of compressors isentropic efficiency to (90 %) has improved the heating COP of both refrigerant systems potentially by more than (20 %) and minimized the power consumption by (24 %) under the same operating conditions. 


Keywords


Cascade Heat Pump, Intermediate Temperature, Green Environment, Sustainable Energy, Optimum COP

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References


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