Freezing device, freezing system, and control method of freezing device
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Solution Overview
Problem
Existing freezing devices using CO2 refrigerant face reduced thermal efficiency and increased power loss when operating in low outside air temperatures, as the high-pressure CO2 refrigerant exceeds the required exhaust heat and compressor rotational rate increases, leading to inefficient freezing performance.
Innovation Solution
The system employs a control unit to set a high-pressure target value for the CO2 refrigerant to operate in a subcritical state in the gas cooler when outside air temperature is below a certain threshold, ensuring the CO2 refrigerant remains subcritical and adjusts the target evaporation temperature in the evaporator, thereby optimizing thermal efficiency and reducing compressor load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the CO2 refrigerant is operated in transcritical mode with higher pressure to remove exhaust heat, then the heat removal capacity is improved, but the thermal efficiency is reduced and power loss is increased
Solution Approach 1:
The system dynamically switches between transcritical and subcritical operation modes based on outside air temperature conditions. When the outside air temperature is below the dew point, the system transitions to subcritical mode with lower high-pressure target values, thereby adapting the pressure level to environmental conditions and reducing unnecessary energy loss while maintaining adequate heat removal capacity
Solution Approach 2:
The invention changes the operating pressure parameter of the CO2 refrigerant based on outside air temperature. By setting a lower high-pressure target value in subcritical mode compared to transcritical mode, the system optimizes the pressure parameter to match environmental conditions, reducing compressor work and improving thermal efficiency when extreme high pressure is not required for adequate heat removal
2Power
If the compressor rotational rate is increased to achieve transcritical mode, then the heat removal capacity is improved, but the power consumption is increased
Solution Approach 1:
The compressor rotational rate is dynamically adjusted based on the operating mode. In subcritical mode triggered by low outside air temperature, the system operates with reduced compressor speed compared to transcritical mode, thereby reducing power consumption while maintaining sufficient heat removal capacity through the phase change process in the gas cooler
Solution Approach 2:
The invention changes the compressor speed parameter in response to outside air temperature conditions. By reducing the compressor rotational rate in subcritical mode, the system decreases power consumption while the refrigerant undergoes phase change from superheated vapor to saturated liquid, maintaining effective heat removal without requiring excessive compressor power
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 enhances thermal efficiency and maintains required freezing performance by adjusting the CO2 refrigerant's state to subcritical, reducing power consumption and ensuring heat balance, even at low outside air temperatures.
Implementation Method 1
a compressor configured to compress a CO2 refrigerant
Implementation Method 2
a gas cooler configured to cool a CO2 refrigerant discharged from the compressor
Implementation Method 3
setting a high-pressure target value of the CO2 refrigerant so that the CO2 refrigerant in the gas cooler becomes subcritical
Implementation Method 4
an expansion valve configured to expand a CO2 refrigerant supplied from the gas cooler
Implementation Method 5
an evaporator configured to evaporate the CO2 refrigerant guided from the expansion valve
Data Source
Figure 1
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AI summary
Provided is a freezing device (1) that can improve thermal efficiency even in a low outside air temperature and obtain necessary freezing performance. The freezing device includes: a compressor (3) configured to compress a CO2 refrigerant; a gas cooler (5) configured to cool a CO2 refrigerant discharged from the compressor (3); and a control unit configured to set a high-pressure target value of the CO2 refrigerant so that the CO2 refrigerant in the gas cooler (5) becomes subcritical and perform subcritical control when an outside air temperature is less than a first predetermined temperature, which is lower than the critical point of the CO2 refrigerant, and a target evaporation temperature in an evaporator to which the CO2 refrigerant cooled by the gas cooler (5) is guided via an expansion valve (7) is less than or equal to a second predetermined temperature.