Economizer Pump Down Control to Reduce Compressor Liquid Flood Back
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Scroll type compressors in refrigeration systems are prone to liquid flood back and slugging due to repeated on-off cycling, leading to increased stress and potential failure, especially when excess capacity exceeds load demand.
Innovation Solution
Implementing a method that involves calculating the difference in saturation temperature and ambient temperature, using an electronic valve assembly to perform a pump down operation when the temperature difference is within a threshold, reducing pressure in the evaporator and compressor suction port to prevent liquid accumulation and reduce stress on the compressor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If repeated on-off cycling is used to maintain desired temperatures when excess compressor capacity exceeds load demand, then energy efficiency is improved, but compressor reliability deteriorates due to increased flooding risk
Solution Approach 1:
The system performs a pump down operation before compressor shutdown to remove refrigerant from the evaporator and economizer heat exchanger. This preliminary action prevents liquid accumulation that would cause flooding during subsequent restarts, thereby maintaining compressor reliability while allowing repeated on-off cycling for energy efficiency.
Solution Approach 2:
The economizer heat exchanger serves as an intermediary component where refrigerant is temporarily stored during pump down operations. By using this intermediate storage location, the system prepares favorable restart conditions without directly impacting compressor operation, resolving the conflict between energy efficiency and reliability.
2Reliability
If pump down operation is performed before compressor shutdown, then compressor reliability is improved by reducing liquid flood back, but system complexity increases
Solution Approach 1:
The controller automatically determines when pump down operations are needed by monitoring saturation temperature and ambient temperature differences. The system self-regulates the pump down timing and duration based on calculated temperature differentials, eliminating the need for additional manual controls or complex external systems while improving reliability.
Solution Approach 2:
The system uses temperature parameter changes (saturation temperature and ambient temperature differential) as the control criterion for initiating pump down operations. By basing the control logic on readily available temperature measurements and simple calculations, the system achieves improved reliability without adding significant complexity.
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
This approach reduces the risk of compressor failure by minimizing liquid flood back and slugging, thereby enhancing compressor life and reliability by maintaining favorable operating conditions during restarts and economizer mode operations.
Implementation Method 1
operating the electronic valve assembly of the refrigeration system includes closing the electronic valve assembly to reduce a pressure within an evaporator of the refrigeration system
Implementation Method 2
determining a difference in a saturation temperature at a port of a compressor of the refrigeration system and an ambient temperature
Data Source
AI summary
A method of operating a refrigeration system includes initiating a compressor shutdown operation, determining a difference in a saturation temperature at a port of a compressor of the refrigeration system and an ambient temperature and comparing the difference in the saturation temperature and ambient temperature with a threshold. If the difference in the saturation temperature and ambient temperature is less than or equal to the threshold, a pump down operation is performed and if the difference in the saturation temperature and ambient temperature exceeds the threshold, a compressor shutdown operation is completed.