Low GWP cascade refrigeration system
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Solution Overview
Problem
Existing refrigeration systems face challenges in meeting the sub 500 Global Warming Potential (GWP) goal while avoiding flammability and toxicity issues, especially for indoor use, and dealing with the complexity and cost of supercritical CO2 refrigeration systems.
Innovation Solution
A cascade refrigeration system design is employed, where the low stage uses R744 (CO2) indoors and the high stage uses sub 500 GWP A2L refrigerants outdoors, with thermal energy storage to manage pressure and prevent refrigerant release during power outages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If R744 (CO2) is used as refrigerant to achieve sub 500 GWP, then environmental performance is improved, but discharge pressure becomes excessively high requiring supercritical operation
Solution Approach 1:
The refrigeration system is divided into two separate stages: a low-stage CO2 refrigeration cycle operating at high pressure for cooling, and a high-stage refrigeration cycle operating at lower pressure for heat rejection. This segmentation allows each stage to operate within optimal pressure ranges, avoiding the need for supercritical operation while maintaining sub-500 GWP performance.
2Device complexity
If R744 refrigeration system operates without thermal management during power outage, then system simplicity is maintained, but refrigerant pressure exceeds safety limits causing premature release
Solution Approach 1:
A thermal energy storage medium is positioned within the refrigerant receiver to preemptively manage refrigerant temperature and pressure during power outages. This preliminary thermal management action prevents pressure from rising to dangerous levels, eliminating the need for premature refrigerant release while maintaining system reliability.
3Quantity of substance
If natural refrigerants R717, R744, R290 are used to achieve low GWP, then environmental performance is improved, but safety issues (toxicity, pressure, flammability) arise
Solution Approach 1:
The system segments different refrigerant functions into separate stages: R744 handles the low-stage refrigeration cycle where its high pressure is manageable, while the high-stage system uses a different refrigerant optimized for heat rejection at lower pressures. This segmentation isolates the harmful characteristics of each natural refrigerant to specific operational contexts where they can be controlled.
4Ease of operation
If R744 system allows refrigerant to warm up during power outage, then passive thermal management is maintained, but pressure reaches 1,108 psi exceeding tank operating limits
Solution Approach 1:
The thermal energy storage medium is pre-positioned in the refrigerant receiver to actively absorb heat and maintain refrigerant temperature during power outages. This preliminary thermal intervention prevents the passive warming that would otherwise occur, keeping pressure well below the 1,108 psi danger threshold and eliminating the need for active pressure management during outages.
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 design achieves efficient sub 500 GWP refrigeration with reduced pressure and component costs, while ensuring safety and preventing premature refrigerant release during power outages, thus addressing the limitations of existing systems.
Implementation Method 1
a heat exchanger configured to transfer heat from the low stage refrigerant to the high stage refrigerant
Implementation Method 2
positioning a thermal energy storage medium within the refrigerant receiver to prevent the refrigerant pressure from building up to a point where the refrigerant would be released from the system in the event of a power outage
Data Source
AI summary
A refrigeration system having a low stage and a high stage circuit. Each stage having a compressor, an evaporator or a condenser. The low stage includes a low stage refrigerant comprising R744. The high stage includes a high stage refrigerant having a GWP less than 500. The system further includes a heat exchanger configured to transfer heat from the low stage refrigerant to the high stage refrigerant allowing the circuits to provide cooling in two stages.