CO2 refrigeration system with supercritical subcooling control
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Solution Overview
Problem
CO2 refrigeration systems face challenges in controlling subcooling effectively, particularly when the refrigerant is in a supercritical region, as traditional methods rely on subcritical saturation pressures which are not applicable in supercritical conditions, leading to inefficiencies in heat transfer and energy usage.
Innovation Solution
A refrigeration system that includes a controller to determine whether the CO2 refrigerant is in a subcritical or supercritical region, using measured temperature and pressure data to calculate pseudo-saturated pressures, allowing the pressure control valve to adjust the refrigerant pressure to achieve desired subcooling levels by generating a supercritical pseudo-saturation function and operating the pressure control valve to drive the refrigerant to the corresponding pseudo-saturated pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional subcritical saturation pressure control methods are used, then subcooling control is effective in subcritical regions, but the method becomes inapplicable and inefficient in supercritical regions
Solution Approach 1:
The patent introduces a pseudo-saturation pressure parameter that dynamically adapts to both subcritical and supercritical regions. By calculating pseudo-saturation pressure based on refrigerant temperature and comparing it with actual pressure, the system maintains effective subcooling control across different thermodynamic states, resolving the inapplicability of traditional subcritical-only methods in supercritical regions
Solution Approach 2:
The control method transitions from static subcritical saturation pressure to dynamic pseudo-saturation pressure that automatically adjusts based on refrigerant temperature. The pseudo-saturation pressure is recalculated continuously using temperature-dependent relationships, enabling the system to adapt to changing operating conditions and maintain optimal heat transfer efficiency in both subcritical and supercritical regions
2Temperature
If pressure is increased to achieve subcooling in subcritical region, then subcooling setpoint is achieved, but latent heat transfer capability is lost in supercritical region
Solution Approach 1:
The system continuously monitors refrigerant temperature and uses this feedback to calculate the corresponding pseudo-saturation pressure. By comparing actual pressure with pseudo-saturation pressure, the controller determines whether the refrigerant is in subcritical or supercritical state and adjusts the pressure control valve accordingly, maintaining optimal heat transfer characteristics in both regions
Solution Approach 2:
The patent employs temperature-dependent pseudo-saturation pressure calculation that changes the control target based on refrigerant state. In subcritical regions, traditional saturation pressure relationships apply; in supercritical regions, the pseudo-saturation pressure is calculated using alternative relationships that account for the absence of distinct phase boundaries, thereby preserving effective heat transfer across both regimes
3Use of energy by moving object
If non-subcooling control schemes are implemented for supercritical systems, then system COP can be maximized, but precise subcooling control is lost
Solution Approach 1:
The patent replaces traditional mechanical pressure control with a sophisticated control algorithm that calculates pseudo-saturation pressure based on temperature measurements. This substitution of mechanical control with intelligent algorithmic control enables precise subcooling management in supercritical regions while maintaining optimal system COP, overcoming the limitations of both traditional subcooling control and non-subcooling optimization schemes
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 enables efficient subcooling control in both subcritical and supercritical regions, optimizing heat transfer and energy usage by ensuring the CO2 refrigerant reaches the desired pseudo-saturated pressure, thereby enhancing the overall performance of the CO2 refrigeration system.
Implementation Method 1
a gas cooler/condenser configured to remove heat from a refrigerant
Implementation Method 2
a pressure control valve located along the high pressure conduit and operable to regulate the pressure of the refrigerant
Data Source
AI summary
A refrigeration system includes a gas cooler/condenser configured to remove heat from a refrigerant, a temperature sensor configured to measure a temperature of the refrigerant leaving the gas cooler/condenser, a pressure sensor located along the high pressure conduit and configured to measure a pressure of the refrigerant leaving the gas cooler/condenser, a pressure control valve operable to regulate the pressure of the refrigerant leaving the gas cooler/condenser, and a controller. The controller is configured to determine whether the refrigerant leaving the gas cooler/condenser is in a subcritical region based on at least one of the measured temperature of the refrigerant or the measured pressure of the refrigerant. If the refrigerant leaving the gas cooler/condenser is not in the subcritical region, the controller is configured to add a pseudo-subcooling temperature value to the measured temperature of the refrigerant to calculate a summed temperature, calculate a supercritical pseudo-saturated pressure as a function of the summed temperature, and operate the pressure control valve to drive the pressure of the refrigerant leaving the gas cooler/condenser to the supercritical pseudo-saturated pressure corresponding to the summed temperature.