Refrigeration cycle apparatus
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Solution Overview
Problem
Existing refrigeration cycle systems using carbon dioxide as refrigerant face challenges with incompatible refrigerating machine oils, leading to inefficiencies and operational limitations.
Innovation Solution
A refrigeration cycle apparatus with a binary refrigerant circuit comprising a first circuit for HFC or HFO refrigerants and polyvinyl ether oil, and a second circuit for carbon dioxide and polyalkylene glycol oil, utilizing a cascade heat exchanger and a control unit to manage the temperature and pressure of carbon dioxide refrigerant and refrigerating machine oil to achieve equal densities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If carbon dioxide refrigerant and incompatible refrigerating machine oil are sealed in the refrigerant circuit, then the refrigeration system can operate with carbon dioxide refrigerant, but the incompatible oil leads to operational limitations and inefficiencies
Solution Approach 1:
The refrigeration system is divided into two separate circuits: a first circuit for HFC or HFO refrigerants with polyvinyl ether oil, and a second circuit for carbon dioxide refrigerant with polyalkylene glycol oil. This segmentation eliminates compatibility issues by isolating incompatible refrigerant-oil pairs into separate systems while allowing each to operate optimally.
Solution Approach 2:
The system employs composite refrigeration architecture combining two distinct refrigeration cycles with different refrigerant types (HFC/HFO and carbon dioxide) and their respective compatible oils. This composite structure leverages the advantages of each refrigerant type while avoiding their individual limitations through proper pairing with compatible lubricants.
2Adaptability or versatility
If a single refrigerant circuit is used, then the system structure is simple, but it cannot achieve simultaneous cooling and heating operations with heat recovery
Solution Approach 1:
The system separates refrigeration functions into independent circuits that can operate simultaneously in different modes. The first circuit handles cooling operations while the second circuit handles heating operations, enabling simultaneous cooling and heating across different locations or applications.
Solution Approach 2:
Each circuit is designed to perform multiple functions: the first circuit can provide cooling and the second circuit can provide heating, allowing the overall system to serve multiple thermal needs simultaneously. The cascade heat exchanger enables heat recovery by transferring heat between the two circuits.
3Reliability
If carbon dioxide refrigerant is used without density control, then the system operates simply, but the density difference between carbon dioxide refrigerant and refrigerating machine oil causes operational problems
Solution Approach 1:
The control unit actively manages temperature and pressure parameters in the second circuit to maintain the density of carbon dioxide refrigerant equal to or greater than the density of polyalkylene glycol oil. By dynamically adjusting these parameters, the system ensures proper phase separation and prevents oil accumulation in the refrigerant circuit.
Solution Approach 2:
The control unit continuously monitors the state of the refrigerant and oil in the second circuit and adjusts operating conditions to maintain the required density relationship. This feedback control ensures stable operation by preventing conditions that would lead to operational problems.
4Productivity
If incompatible refrigerating machine oil is used with carbon dioxide, then the system can be simplified, but heat load management becomes unbalanced
Solution Approach 1:
The binary circuit architecture separates heat management functions, allowing each circuit to be optimized for its specific refrigerant type and heat transfer characteristics. This enables balanced heat load management across different thermal zones or applications.
Solution Approach 2:
By controlling temperature and pressure parameters in the second circuit, the system optimizes the thermal properties of carbon dioxide refrigerant and polyalkylene glycol oil mixture, ensuring efficient heat transfer and balanced heat load distribution across the system.
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
Enhances operational efficiency and flexibility by allowing simultaneous cooling and heating operations, with heat recovery capabilities and balanced heat load management across multiple utilization units.
Implementation Method 1
The cascade heat exchanger heats the carbon dioxide refrigerant with the first refrigerant
Implementation Method 2
The control unit controls operation of the first circuit so that a temperature or pressure of the carbon dioxide refrigerant and the refrigerating machine oil in the container is equal to or higher than a predetermined temperature or predetermined pressure corresponding to a boundary temperature at which a density of the carbon dioxide refrigerant and a density of the refrigerating machine oil in the container become equal
Data Source
AI summary
A refrigeration cycle apparatus includes a first circuit, a second circuit, a cascade heat exchanger, and a control unit. The first circuit circulates a first refrigerant. The second circuit circulates a carbon dioxide refrigerant and refrigerating machine oil. The cascade heat exchanger heats carbon dioxide refrigerant with first refrigerant. The second circuit includes a second compressor and a container. The container is provided on suction side of the second compressor. The container stores the carbon dioxide refrigerant and the refrigerating machine oil. The control unit controls the operation of the first circuit so that the temperature or pressure of the carbon dioxide refrigerant and the refrigerating machine oil in the container is equal to or higher than a predetermined temperature or predetermined pressure corresponding to a boundary temperature at which the density of the carbon dioxide refrigerant and the density of the refrigerating machine oil in the container become equal.