Refrigeration Cycle Compressor Heating for Discharge Superheat Control
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Solution Overview
Problem
The target discharge superheat degree sometimes falls below the lower limit value, posing a risk to compressor reliability, especially under conditions of low refrigerant circulation, small differential pressure operation, or use of refrigerants with low specific heat ratios.
Innovation Solution
A refrigeration cycle device with a control device that adjusts the expansion valve opening degree and uses a heating device to warm the compressor when the discharge superheat degree falls below a predetermined limit, ensuring the target discharge superheat degree remains above the compressor's reliability threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the opening degree of the expansion valve is controlled to be small to increase the discharge superheat degree, then the discharge superheat degree increases, but the suction superheat degree also increases and the target discharge superheat degree may not reach the lower limit value under low refrigerant circulation conditions
Solution Approach 1:
The control device changes the target discharge superheat degree from a fixed value to a variable value that adapts to operating conditions. When the refrigerant circulation amount is small, the target discharge superheat degree is increased to ensure it reaches the lower limit value, preventing compressor reliability degradation while maintaining efficient operation under varying load conditions
Solution Approach 2:
The control device continuously monitors the refrigerant circulation amount and adjusts the target discharge superheat degree accordingly. This feedback mechanism ensures that when circulation is low, the system compensates by raising the target discharge superheat degree, preventing the discharge superheat from falling below the critical lower limit that would harm compressor reliability
2Reliability
If a refrigerant with a small specific heat ratio (e.g., R290) is used to improve environmental performance, then the enthalpy increase amount in compression decreases, but the suction superheat degree required to achieve the lower limit discharge superheat degree becomes relatively high
Solution Approach 1:
The system adapts the target discharge superheat degree based on the refrigerant's specific heat ratio characteristics. For refrigerants with small specific heat ratios like R290, the target discharge superheat degree is set higher to compensate for the smaller enthalpy increase during compression, ensuring the discharge superheat reaches the required lower limit without requiring excessively high suction superheat degrees
3Productivity
If the discharge superheat degree is controlled to reach the target value to maintain system efficiency, then the system operates efficiently, but the discharge superheat degree may fall below the lower limit value in low differential pressure operation
Solution Approach 1:
The target discharge superheat degree is made dynamic rather than fixed. The control device adjusts the target value in real-time based on the refrigerant circulation amount and operating conditions. In low differential pressure operation where the circulation amount is small, the target is raised to ensure the discharge superheat degree remains above the lower limit, preventing reliability issues while maintaining efficiency in normal operating conditions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution prevents the target discharge superheat degree from falling below the compressor's lower limit, thereby suppressing reliability issues and maintaining efficient operation.
Implementation Method 1
a heating device configured to heat the compressor
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A refrigerant circuit (9) where a compressor (4), a utilization-side heat exchanger (6) configured to function as a condenser, an expansion valve (7), and a heat-source-side heat exchanger (8) configured to function as an evaporator are connected by a pipe; a discharge superheat degree calculation device (26) configured to calculate the discharge superheat degree of a refrigerant; a heating device (11) configured to heat the compressor; and a control device (25) configured to control the opening degree of the expansion valve, the compressor, and the heating device are provided, and the control device is configured to heat the compressor by the heating device when the discharge superheat degree has fallen below the predetermined discharge-superheat-degree lower limit value and the opening degree of the expansion valve has become equal to or less than the predetermined opening degree.