Thermodynamic Analysis for Hybrid Low Temperature Sustainable Energy Sources in Cascade Heat Pump Technology

A thermodynamic analysis of compound Cascade refrigeration system at low temperature heat sources was conducted. The analysis was based on a target temperature of hot water at the range of (60-70) °C out of the heat pump. The carrier thermal fluid temperature, which provides heat at the low temperature side of the Cascade system, determines the pair of refrigerants to be implemented. A hybrid heat pump design was proposed, which implements the sea water and ground as heat sources in a compound cycle. Two of refrigerant pairs were tested for the performance and energy efficiency comparison at fixed operating conditions. In the low temperature cycle, either R410A or R717 refrigerant was allowed to circulate and R134a is circulated at the high temperature cycle. The minimum isentropic efficiency of commercially available compressors was used in this investigation, a value of (70 %) was chosen. The results of the investigation revealed that R717/R134a exhibited a higher heating (COP) than that of R410A/R134a by (3 %). The results showed that increasing the isentropic efficiency of compressors to (90 %) improved the heating (COP) by (20 %) and minimized the power consumption by (24 %). The specific power consumed by compressors of the proposed system showed a decrease of upto (3 %) lower than that of the sea water base system