• Performance Study of Heat Pump System with Refrigerant Injection
• Author  :  Abdul Hadi N. Khalifa, Johain J. Faraj and Hayder K. Hasan
• Pages   :  238-243
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• Abstract

The current work investigated the performance improvement that can be achieved on heat pump system, through using refrigerant injection technology. A 5 tons heat pump system charged with R22 was modified by adding secondary expansion valve, Liquid Pressure Amplification (LPA) pump, accumulator and receiver. The heat pump performance was improved through three approaches. The first approach was accomplished by injected refrigerant vapour into the accumulator to mix with superheated vapour leaving evaporator. The volume ratio of injected vapour was 1 to 4%. The second was achieved by injected liquid refrigerant from condenser exit by an LPA pump, to the discharge line in a volume ratio of 1 to 5%. A hybrid injection was the third approach, in which both vapour and liquid were injected in suction and discharge lines simultaneously, the vapour volume ratio varied from 1% to 2% while keeping the liquid ratios as above. It was found that, injected vapour in the ratio of 4% improved both cycle PF and overall exergy efficiency by about 2.47% and 3.2% respectively, reduces suction temperature from (-4.89°C) to (-12.48°C) and discharge temperature by 12.74%. The optimum ratio of injected vapour was 3% since an additional increase in the ratio to 4% shows less effect on all the key variables. Injected liquid in the ratio of 3% improved both cycle PF and overall exergy efficiency by about 27.1% and 18.37% respectively, reduces the suction , discharge and condenser inlet temperatures by 29.8%, 17.42% and 24.7% respectively. While hybrid injection improved the cycle PF by 33% and exergy efficiency by 21.45%. From above, it was found that hybrid injection gave optimum results when the volume ratios of injected vapour and liquid were 2% and 3% respectively in comparison to other cases.

Keywords: Refrigeration, Refrigerant injection, Exergy analysis, Heat pump

Article published in International Journal of Thermal Technologies, Vol.5,No.3 (Sept-2015)