Suction superheat conrol based on refrigerant condition at discharge

Abstract

A relationship is developed between a discharge condition of a refrigerant leaving a compressor, and the suction superheat or refrigerant quality. By relying upon measurement and control of the discharge condition, the present invention is able to achieve very low suction superheat values. Controlling the operation to very low suction superheat values results in augmented refrigerant system performance.

Description

BACKGROUND OF THE INVENTIONThis application relates to a refrigerant superheat control to enhance system performance and improve compressor reliability, which relies upon a refrigerant thermodynamic condition at discharge to provide reliable suction superheat control.In air conditioning, heat pump and refrigeration systems, a superheat of the refrigerant leaving an evaporator needs to be closely controlled. Refrigerant leaves the evaporator normally at the superheated thermodynamic state, where its actual temperature is higher than the corresponding saturation temperature (a superheat is defined as the difference between these two temperatures). A certain (positive) superheat is typically required to ensure that little or no liquid refrigerant enters the compressor and system operation is stable. If a significant amount of liquid refrigerant enters the compressor, an undesirable condition known as “flooding” will occur. Flooding could cause “liquid hammer” conditions damaging or bre...

AI Technical Summary

Benefits of technology

The present invention is about controlling the temperature of a refrigerant in a refrigeration system. It uses the fact that changes in the temperature of the refrigerant leaving the compressor are directly related to changes in the discharge temperature. By monitoring the discharge temperature and adjusting the condition of the refrigerant in the evaporator or compressor, the system can operate at a desired low suction superheat or have a minimal amount of liquid refrigerant entering the compressor. This allows for better efficiency and control of the refrigeration system. The relationship between the discharge temperature and suction superheat can be determined experimentally or analytically, and it needs to be periodically tested and adjusted during operation. The invention allows for operation at lower superheat levels and can minimize the amount of liquid refrigerant entering the compressor.

Problems solved by technology

If a significant amount of liquid refrigerant enters the compressor, an undesirable condition known as “flooding” will occur.

Flooding could cause “liquid hammer” conditions damaging or breaking compression elements, dilute lubrication oil and wash it off the bearing surfaces, pump lubrication oil out of the compressor sump, and eventually degrade refrigerant system performance and operation.

Conversely, as the superheat value is increased, refrigerant is boiled off from the oil increasing the oil viscosity and making the oil more susceptible to stagnate in the evaporator exit section or in the piping connecting the evaporator to the compressor.

Also, at some operating conditions, higher suction superheat values lead to elevated discharge temperatures, operational envelope reduction, potential oil breakdown and thermal distortion of compression elements.

It is undesirable, as mentioned above, to have significant flooding in the compressor, due to associated reliability issues.

Thus, the refrigerant system designers have erred on the side of applying sufficient superheat values to eliminate any potential for such flooding at an entire spectrum of operating conditions.

As mentioned above, uncontrolled flooding results in a drastic drop in compressor capacity and efficiency, and may also cause severe damage to the compressor.

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