Refrigerating apparatus and control device for refrigerating machine
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Solution Overview
Problem
Existing refrigeration systems face challenges in achieving efficient operation and accurate surge detection across varying loads and hot gas bypass conditions, with existing methods struggling to maintain accuracy and efficiency, especially at high altitudes and during partial load operations.
Innovation Solution
The system calculates the operating head by considering suction temperature, installation location, and pressure differences between discharge and inlet locations, using a compressor map for precise rotational speed control and surge detection, and includes a chiller controller that adjusts expansion valve openings based on compressor capacity and temperature differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional surge detection methods are used, then the system can operate during normal conditions, but the surge detection accuracy deteriorates during emergency times and varying load conditions
Solution Approach 1:
The patent changes the parameters used for surge detection from conventional single-point measurements to multiple parameters including suction temperature, installation location (altitude), and pressure differences between sensing locations and actual compressor inlet/outlet locations. This multi-parameter approach allows accurate surge detection across varying load conditions and hot gas bypass scenarios by dynamically adjusting the operating head calculation based on these changing parameters.
2Measurement precision
If simple head calculation methods are used, then the calculation is fast and simple, but the accuracy of operating head determination deteriorates
Solution Approach 1:
The patent introduces intermediary correction factors to bridge the gap between simple measurements and accurate head calculation. Specifically, it uses correction factors for suction temperature effects, installation location (atmospheric pressure variations), and pressure drop across the compressor inlet and outlet. These intermediaries allow the system to maintain relatively simple calculation procedures while achieving high accuracy by compensating for various influencing factors.
3Reliability
If rotational speed control is not precisely controlled, then the system operation is simple, but the ability to avoid surge and maintain efficient operation deteriorates
Solution Approach 1:
The patent implements a feedback control system where the calculated operating head is continuously compared with the surge line from the compressor map. Based on this comparison, the controller adjusts the rotational speed of the centrifugal compressor to maintain operation above the surge line. This feedback mechanism ensures reliable surge avoidance while automating the complex control decisions, making the system easy to operate despite the sophisticated control strategy.
Data Source
AI summary
A refrigerating apparatus includes a centrifugal compressor, suction and discharge capacity control mechanisms that control capacity of the compressor by changing opening degrees of the suction and discharge capacity control mechanisms, and a controller that compares a compressor-specific surge curve with an isentropic head to perform rotational speed control of the compressor, rotational speed adjustment control of the compressor in order to avoid surge, and emergency shutdown control of the compressor upon detection of surge. The compressor-specific surge curve is stored in the controller in advance, and is defined by an actual rotational speed of the compressor and opening degrees of the suction and discharge capacity control mechanisms. The isentropic head is calculated based on a suction pressure, a discharge pressure, and a suction temperature during operation.