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, face challenges in efficiently controlling capacity without direct feedback on the slide valve's position, leading to suboptimal performance and energy inefficiencies.
Innovation Solution
A controller system that uses temperature and pressure sensors to determine the need for loading or unloading the compressor by sending load or unload commands to the slide valve based on setpoints and timers, allowing for capacity modulation without requiring feedback on the slide valve's current position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional capacity control methods are used without direct feedback on slide valve position, then device complexity is reduced, but control precision and reliability deteriorate
Solution Approach 1:
The patent implements feedback by using temperature and pressure sensors to indirectly determine slide valve position. The controller monitors these parameters and infers the valve position state, creating a closed-loop control system that achieves precise control without direct position sensors, thus resolving the contradiction between reduced complexity and maintained precision.
Solution Approach 2:
The patent uses temperature and pressure as intermediary parameters to determine slide valve position. Instead of directly measuring valve position, the system measures temperature and pressure changes that result from valve movement, using these intermediaries to infer the actual valve state and achieve precise control indirectly.
2Ease of operation
If capacity control is implemented without accurate slide valve position detection, then ease of operation is improved, but energy efficiency deteriorates
Solution Approach 1:
The feedback mechanism using temperature and pressure sensors allows the controller to accurately determine when the slide valve has reached its target position. This enables precise capacity control that matches actual system needs, preventing energy waste from over-compression while maintaining ease of operation through automatic control.
Solution Approach 2:
The patent replaces direct mechanical position detection with thermal and pressure-based sensing. This substitution maintains ease of operation by eliminating complex mechanical position sensors while improving energy efficiency through more accurate detection of actual compression capacity and slide valve position.
3Device complexity
If simple control methods are used for capacity modulation, then device complexity is reduced, but reliability of temperature control deteriorates
Solution Approach 1:
The feedback loop continuously monitors temperature and pressure parameters, allowing the controller to reliably determine slide valve position and adjust capacity accordingly. This maintains temperature control reliability while keeping the system relatively simple by using readily available sensor data rather than complex direct position measurement systems.
Solution Approach 2:
By using temperature and pressure as intermediary measurement parameters, the system achieves reliable temperature control through indirect but accurate detection of compression capacity. This approach maintains reliability while avoiding the complexity of direct slide valve position sensing mechanisms.
Data Source
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AI summary
A compressor system includes a screw compressor (48) and a controller (100). The screw compressor includes a slide valve (49) 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 example embodiment, the controller (100) does not receive feedback from the screw compressor (48) regarding a position of the slide valve (49).