Economizer Circuit Control for Compressor Current and Cooling Capacity
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Solution Overview
Problem
Refrigeration or chiller systems face challenges in controlling motor current while maintaining desired cooling capacity, particularly when using variable speed drives, as reducing compressor speed leads to larger reductions in cooling capacity compared to other unloading techniques like slide valve unloading in screw compressors.
Innovation Solution
A method and system for controlling an economizer circuit by measuring liquid levels in a flash tank and compressor operating parameters, using a valve to control the flow of refrigerant to the compressor, which includes a controller connected to sensors for determining liquid levels and compressor frequency, allowing for incremental valve adjustments to manage refrigerant flow based on predetermined conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If variable speed drive is used to reduce compressor speed for controlling motor current, then motor current is reduced, but cooling capacity is reduced to a larger extent
Solution Approach 1:
The refrigerant flow to the compressor is segmented into two separate controllable paths: the main suction line and the economizer line. By independently controlling these paths through separate valves (suction service valve and economizer valve), the system can selectively unload the compressor without reducing overall compressor speed, thereby maintaining cooling capacity while controlling motor current.
Solution Approach 2:
The economizer circuit acts as an intermediary mechanism that provides a controlled path for refrigerant flow. By introducing the economizer valve as a mediator between the flash tank and compressor, the system can modulate refrigerant flow to the compressor independently of compressor speed, enabling current control without proportional capacity loss.
2Productivity
If slide valve unloading is used in screw compressors, then cooling capacity is maintained better, but device complexity increases
Solution Approach 1:
The economizer circuit serves as an intermediary unloading mechanism that avoids the complexity of slide valves. By using the existing economizer infrastructure with simple on/off valves controlled by a controller, the system achieves capacity modulation without mechanical sliding components, reducing device complexity while maintaining cooling capacity.
Solution Approach 2:
The mechanical slide valve unloading mechanism is replaced with an electronically controlled valve system. The controller uses sensor inputs to automatically modulate the economizer valve, substituting complex mechanical sliding components with simpler electronically actuated valves, thereby reducing device complexity while maintaining functional equivalence.
3Reliability
If economizer circuit is operated selectively based on liquid level and operating parameters, then component damage is prevented and performance is enhanced, but control system complexity increases
Solution Approach 1:
The control system incorporates feedback from multiple sensors (liquid level sensor, temperature sensor, pressure sensor) that continuously monitor system conditions. The controller uses this feedback to automatically adjust valve positions, ensuring the economizer circuit operates only under appropriate conditions, thereby preventing component damage while using a relatively simple control architecture.
Solution Approach 2:
The control system is designed to automatically monitor and adjust economizer operation based on predetermined conditions without requiring complex external control. The controller self-regulates the economizer valve based on sensor inputs, and the system can automatically disable the economizer when conditions are inappropriate, providing self-service protection with minimal 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 allows for enhanced compressor and system performance by selectively operating the economizer circuit, preventing conditions that could damage components, and maximizing cooling capacity without significant reductions in cooling capacity, while maintaining low costs by avoiding expensive unloading mechanisms.
Implementation Method 1
Upon passing through the expansion device, the liquid refrigerant experiences a pressure drop, whereupon, at least a portion of the refrigerant rapidly expands or 'flashes' and is converted from a liquid to a gas
Implementation Method 2
The liquid refrigerant in the flash tank collects at the 'bottom' of the flash tank and returns to the main refrigerant circuit through the first outlet line. The gaseous refrigerant in the flash tank collects at the 'top' of the flash tank
Implementation Method 3
Upon passing through the expansion device, the liquid refrigerant experiences a pressure drop
Implementation Method 4
at least a portion of the refrigerant rapidly expands or 'flashes' and is converted from a liquid to a gas
Implementation Method 5
the economizer circuit can improve system efficiency by providing refrigerant gas at an intermediate pressure to the compressor, thereby reducing the amount of work required by the compressor and increasing compressor efficiency
Data Source
AI summary
A method for controlling an economizer circuit is provided. The economizer circuit includes a valve to regulate refrigerant flow between the economizer and the compressor. The valve can be opened to engage the economizer circuit or closed to disengage the economizer circuit based on the output frequency provided to the compressor motor by a variable speed drive and an operating condition of the economizer.