Capacity control for chillers having screw compressors
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Solution Overview
Problem
Existing compressor systems for refrigeration circuits, particularly those with screw compressors, lack efficient capacity modulation capabilities without feedback on the slide valve position, leading to suboptimal performance in maintaining chilled fluid temperature setpoints.
Innovation Solution
A controller system that communicates with a slide valve in the screw compressor to modulate capacity by receiving chilled fluid temperature setpoints and data, providing load or unload commands based on temperature differences, without requiring feedback on the slide valve's position, thereby adjusting the compressor's capacity to match the desired temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the compressor system uses a slide valve to modulate capacity, then the ability to adjust capacity is improved, but the complexity of controlling the slide valve position increases
Solution Approach 1:
The patent extracts the feedback mechanism from the control system, operating the slide valve without position feedback. This removes the complexity of feedback sensors and control loops while maintaining capacity modulation capability through open-loop control based on temperature differential
Solution Approach 2:
The system uses the natural temperature differential between chilled fluid and setpoint as a self-regulating signal. The controller automatically adjusts capacity based on this inherent feedback from the process itself, eliminating the need for additional position feedback mechanisms
2Measurement precision
If the controller receives feedback on slide valve position, then the precision of capacity control is improved, but the number of sensors and feedback mechanisms increases
Solution Approach 1:
The patent uses temperature feedback instead of position feedback. The chilled fluid temperature and setpoint differential serve as the feedback signal, providing sufficient control precision without requiring slide valve position sensors
Solution Approach 2:
The temperature differential acts as an intermediary signal that indirectly indicates the required capacity adjustment. This mediator provides control information without requiring direct measurement of the slide valve position
3Device complexity
If the compressor operates without feedback on slide valve position, then the device complexity is reduced, but the ability to maintain precise temperature setpoints may be compromised
Solution Approach 1:
The control system uses the process temperature itself as the regulation signal. The temperature differential between actual chilled fluid temperature and setpoint directly drives capacity adjustments, creating a self-regulating system that maintains reliability without complex feedback
Solution Approach 2:
The system changes the control parameter from slide valve position to temperature differential. This parameter change simplifies the control system while maintaining or improving temperature setpoint maintenance through direct temperature-based control
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 solution enables precise control of the compressor's capacity, ensuring the chilled fluid temperature is maintained within setpoints, improving the efficiency and effectiveness of the refrigeration process.
Implementation Method 1
The evaporator is configured to subject the refrigerant to a heat exchange relationship with a fluid
Data Source
AI summary
A compressor system includes a screw compressor and a controller. The screw compressor includes a slide valve selectively actuatable between a first position and a second position to facilitate modulating a capacity of the screw compressor between fully-loaded and fully-unloaded. The controller is communicably coupled to the slide valve. The controller is configured to receive a chilled fluid temperature setpoint for a fluid in heat transfer communication with a refrigerant of the refrigeration circuit; receive temperature data indicative of a chilled fluid temperature of the fluid; determine a difference between the chilled fluid temperature and the chilled fluid temperature setpoint; and provide one of a load command and an unload command to the slide valve based the difference between the chilled fluid temperature and the chilled fluid temperature setpoint. According to an embodiment, the controller does not receive feedback from the screw compressor regarding a position of the slide valve.