Parallel Chiller Control Using Pressure-Based Load Estimation
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Solution Overview
Problem
In parallel-type chillers with partitioned evaporators and condensers, direct measurement of cooling water temperature at the mid-position is not possible, hindering accurate load calculation and compressor capacity control, leading to inefficient control of compressors and expansion valves.
Innovation Solution
A control apparatus that estimates the terminal temperature difference in the upstream-side space based on the saturation temperature of the second fluid and measured exit temperature, allowing for the estimation of the first fluid's temperature near the exit, enabling accurate load calculation and independent control of compressors and valves without the need for a level sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a partition plate is installed to divide the evaporator and condenser into upstream and downstream spaces, then individual compressor control becomes possible, but direct temperature measurement at the mid-position becomes impossible
Solution Approach 1:
The patent uses refrigerant pressure as an intermediary parameter to indirectly determine the temperature at the mid-position of the evaporator. By measuring the refrigerant pressure in the upstream space and converting it to saturation temperature, the system obtains temperature information without requiring direct temperature measurement at the partitioned mid-position.
Solution Approach 2:
The patent replaces the mechanical/physical temperature measurement system (thermometer) with a pressure-based measurement and conversion system. Instead of using a temperature sensor at the mid-position, the system uses pressure sensors to measure refrigerant pressure and converts it to temperature through saturation temperature calculation.
2Productivity
If multiple compressors are used to increase cooling capacity, then system productivity improves, but control accuracy deteriorates due to inability to calculate individual load
Solution Approach 1:
The patent divides the refrigeration system into separate upstream and downstream spaces with distinct compressors, allowing independent load calculation for each compressor. By partitioning the system and assigning specific compressors to specific spaces, the patent enables individual load assessment based on temperature difference and refrigerant flow in each segmented region.
Solution Approach 2:
The patent uses refrigerant flow rate and temperature difference as intermediary parameters to calculate the load of each compressor. By measuring these parameters in each segmented space and combining them with the estimated mid-position temperature, the system accurately determines individual compressor load without requiring direct measurement at the partition boundary.
3Ease of operation
If expansion valve control is performed using refrigerant level as indicator, then control simplicity is maintained, but control accuracy deteriorates
Solution Approach 1:
The patent changes the control parameter from refrigerant level to refrigerant pressure and temperature difference. By using pressure and temperature as control parameters instead of liquid level, the system achieves more accurate expansion valve control while maintaining operational simplicity through electronic sensing and control algorithms.
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
Improves the accuracy and efficiency of compressor capacity control, reduces the necessity for a level sensor, and enhances performance by allowing individual compressor control and avoiding surging.
Implementation Method 1
multiple shell-and-tube-type heat exchangers each of which includes a tube through which first fluid flows, a shell in which second fluid flows outside the tube
Implementation Method 2
estimates a terminal temperature difference in the upstream-side space on the basis of a terminal temperature difference between a saturation temperature of the second fluid and a measured exit temperature value
Data Source
AI summary
A control apparatus for a parallel-type chiller provided with multiple shell-and-tube-type heat exchangers and multiple compressors, the control apparatus having an estimation section which estimates a terminal temperature difference in an upstream-side space on the basis of a terminal temperature difference between a saturation temperature of a second fluid and a measured exit temperature value, the saturation temperature being estimated on the basis of a pressure value of the second fluid in a downstream-side space, the measured exit temperature value being a temperature of the first fluid measured at an exit of the heat exchanger, and estimates a temperature of the first fluid in the vicinity of an exit of the upstream-side space on the basis of the terminal temperature difference in the upstream-side space and the saturation temperature of the second fluid in the upstream-side space.