Abstract
The operation and performance of heat-pump systems are affected by indoor and outdoor operating conditions. Power consumption and system efficiency are related to evaporator and condenser working pressures. Intelligent controllers such as a proportional integral (PI) controller improve the performance of variable speed refrigeration systems (VSRs) with electronic expansion valve (EEV). Evaporator and condenser pressures affect the system power consumption and efficiency. In this study, the influence of evaporator and condenser temperatures on the performance of a variable speed refrigeration system with an EEV was experimentally investigated at constant cooling load. The experimental system comprises of a rotary compressor, shell-and-coil condenser, EEV, and shell-and-coil evaporator for one-ton cooling capacity with refrigerant R410. Compressor speed and EEV opening are controlled by a PI controller with two control loops and the refrigerant superheat (DS) is maintained at 7°C. The results show that at constant cooling capacity, the refrigerant flow rate rises with the increase in the compressor speed. The coefficient of performance (COP) is improved with low compressor speed. The System COP is increased by 3.3% with increasing evaporator inlet water temperature for 2°C due to the reduction in the compressor speed and compression ratio. High condenser inlet water temperature promotes the refrigerant subcooling.
Highlights
Energy saving in variable speed refrigeration system (VSRs) depends on the pressure ratio between condenser and evaporator pressures that is related to their working temperatures and on the compressor’s speed [1]
Narrow electronic expansion valve (EEV) opening affected the amount of refrigerant subcooled at certain compressor speed which led to increasing refrigeration capacity
The performance was studied by the effects of evaporator and condenser inlet water temperatures on the system coefficient of performance (COP), refrigerant flow, evaporator, and condenser pressures at steady state conditions
Summary
Energy saving in variable speed refrigeration system (VSRs) depends on the pressure ratio between condenser and evaporator pressures that is related to their working temperatures and on the compressor’s speed [1]. The effect of compressor speed variation and EEV opening on the power consumption and refrigeration rate in cooling chiller systems was numerically investigated by Koury et al [2]. The results of a numerical simulation showed that when the compressor speed increased, the COP decreased because of higher power consumption in spite of the increase in refrigeration effect. The effects of operating conditions on system power consumption were investigated by Aprea et al [3] for cooling and heating modes. They compared between constant frequency reciprocating compressor and variable frequency scroll compressor refrigeration systems. The experimental results showed that constant speed compressor consumed higher energy compared to variable speed compressor at all operating conditions. Narrow EEV opening affected the amount of refrigerant subcooled at certain compressor speed which led to increasing refrigeration capacity
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