Method for controlling gas pressure in cooling plant
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Solution Overview
Problem
Cooling plants with heat rejecting heat exchangers face inefficiencies due to 'gas loop operation' caused by faults in pressure and temperature measurements, leading to suboptimal energy use and reduced cooling capacity.
Innovation Solution
A method to detect and recover from gas loop operation by monitoring compressor capacity and pressure in the heat rejecting heat exchanger, using a control unit to adjust pressure and duration of compressor operation to identify and exit gas loop mode efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gas cooler control is used with standard pressure and temperature measurement, then the system operates with simple control logic, but measurement faults cause gas loop operation reducing cooling capacity to almost zero
Solution Approach 1:
The control system proactively detects potential gas loop conditions by monitoring compressor capacity and pressure trends before they fully develop into harmful gas loop operation. By establishing a period of time elapsed counter when compressor capacity reaches a pre-set percentage of maximum capacity, the system takes preliminary action to prevent the harmful condition rather than reacting after damage occurs.
Solution Approach 2:
The system continuously monitors compressor capacity, pressure, and time elapsed to detect gas loop conditions. When the period of time elapsed exceeds a pre-set threshold, the controller provides feedback by adjusting the reference pressure for the gas cooler to move the operating point away from the dangerous region in the log P-h diagram, thereby restoring efficient operation.
2Productivity
If the controller increases compressor capacity to 100% during gas loop operation, then the system attempts to recover cooling capacity, but energy efficiency remains poor during the recovery period
Solution Approach 1:
By detecting gas loop conditions early through monitoring compressor capacity and pressure trends, the system takes preliminary action to adjust the gas cooler reference pressure before cooling capacity drops to near zero. This prevents the need for extreme compressor capacity increases and maintains better energy efficiency throughout the recovery process.
3Measurement precision
If small pressure measurement errors occur in the gas cooler, then the control system believes it is operating optimally, but the actual operation point shifts dramatically reducing efficiency
Solution Approach 1:
The system uses feedback from multiple parameters (compressor capacity, pressure, and time elapsed) to detect when small measurement errors have caused the system to operate in a harmful gas loop region. The controller continuously adjusts the gas cooler reference pressure based on this feedback to maintain optimal operation despite measurement uncertainties.
Solution Approach 2:
The system applies a conservative approach by establishing a pre-set percentage threshold for compressor capacity and a pre-set period of time threshold. When these thresholds are exceeded, the controller takes action to adjust the gas cooler reference pressure, even if the measurement error is small, to prevent potential gas loop operation. This excessive caution ensures reliability over absolute precision.
Data Source
AI summary
A method for monitoring gas pressure in a heat rejecting heat exchanger in a cooling circuit is disclosed. The present capacity of one or more compressors in the cooling circuit compared to a maximum capacity of the one or more compressors is established. If the present capacity of the one or more compressors is at least at a level corresponding to a pre-set percentage of the maximum capacity, a period of time elapsed from a point in time where the compressor capacity reached said level is established. If the established period of time has a duration which is longer than a pre-set period of time, then it is concluding that the cooling medium is in a gas loop operational mode, allowing an operator or a controller to adjust operation of the cooling plant such that the cooling medium is brought out of the gas loop operational mode.