Subcritical CO<sub>2 </sub>refrigeration system using thermal storage
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Solution Overview
Problem
Carbon dioxide (CO2) transcritical refrigeration systems in commercial refrigerated display cases consume more energy and have inefficiencies due to higher operating pressures, requiring costly materials and skilled labor, and often operate inefficiently due to fluid density changes and critical temperature limitations.
Innovation Solution
A subcritical CO2 refrigeration system is designed with a primary refrigeration circuit and a secondary refrigeration circuit using a thermal storage unit with phase change material (PCM) to maintain subcritical operation by providing cooling to the CO2 refrigerant when it exceeds its critical temperature, and vice versa, optimizing energy use and system efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If transcritical CO2 refrigeration systems are used, then refrigeration cooling effect is achieved, but energy consumption increases due to higher operating pressures
Solution Approach 1:
The system dynamically adjusts operating parameters (pressure, temperature) to maintain subcritical operation of CO2 refrigerant by using the thermal storage unit to control refrigerant temperature, thereby reducing energy consumption while avoiding excessively high pressures
Solution Approach 2:
A thermal storage unit containing phase change material is introduced as an intermediary between the CO2 refrigerant and the environment. This thermal storage unit absorbs or releases heat to maintain the CO2 refrigerant temperature below its critical point, enabling subcritical operation and reducing energy consumption
2Productivity
If transcritical CO2 refrigeration systems are used, then refrigeration cooling effect is achieved, but system efficiency decreases due to fluid density changes
Solution Approach 1:
The system maintains CO2 refrigerant in subcritical state by controlling temperature through the thermal storage unit, which stabilizes fluid density and improves system efficiency by avoiding the large density changes that occur near the critical point
3Use of energy by moving object
If transcritical CO2 refrigeration systems are used, then refrigeration cooling effect is achieved, but material costs increase to withstand higher pressures
Solution Approach 1:
By maintaining subcritical operation of the CO2 refrigerant through the thermal storage unit, the system operates at lower pressures that can be handled by standard materials and conventional manufacturing techniques, reducing material costs while still achieving effective refrigeration cooling
4Use of energy by moving object
If transcritical CO2 refrigeration systems are used, then refrigeration cooling effect is achieved, but labor costs increase requiring more skilled technicians
Solution Approach 1:
The thermal storage unit acts as a buffer that simplifies system operation by automatically regulating CO2 refrigerant temperature. This intermediary device reduces the complexity of controlling subcritical operation, making the system easier to operate and maintain with less skilled labor
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
The subcritical CO2 refrigeration system reduces energy consumption, enhances system efficiency, and lowers operational costs by utilizing phase change materials to manage CO2 refrigerant conditions effectively, thereby improving the overall performance and reducing material and labor expenses.
Implementation Method 1
The thermal storage unit contains a phase change material. The phase change material provides cooling to the primary refrigerant during a first operating condition. The phase change material is configured to maintain subcritical operation of the primary refrigeration circuit during the first operating condition when the primary refrigerant would otherwise be above the critical temperature.
Implementation Method 2
The thermal storage unit contains a phase change material. The phase change material provides cooling to the primary refrigerant during a first operating condition.
Implementation Method 3
The secondary refrigeration circuit is in thermal communication with the primary refrigeration circuit through the heat exchanger.
Data Source
AI summary
A refrigeration system includes a primary refrigeration circuit configured to circulate a CO2 primary refrigerant and a secondary refrigeration circuit separate from the primary refrigeration circuit. The primary refrigeration circuit includes a compressor assembly, a condenser assembly, a receiver, and one or more refrigeration loads having an evaporator assembly. The secondary refrigeration circuit includes a thermal storage unit and a heat exchanger. The thermal storage unit contains a phase change material. The secondary refrigeration circuit is in thermal communication with the primary refrigeration circuit through the heat exchanger. The primary refrigerant includes a critical temperature. The primary refrigeration circuit is configured for subcritical operation. The primary refrigeration circuit and the secondary refrigeration circuit are configured such that the phase change material provides cooling to the primary refrigerant during a first operating condition. The phase change material is configured to maintain subcritical operation of the primary refrigeration circuit during the first operating condition when the primary refrigerant is above the critical temperature.