Intercooler and Vapor Injection for CO2 Discharge Temperature Control
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Solution Overview
Problem
Refrigerant systems with multi-stage compressors, particularly those using CO2, face high discharge temperatures due to high operating pressures and transcritical cycles, leading to reduced efficiency and reliability, and the additional cost of intercoolers and liquid/vapor injection systems is not justified by their limited benefits in conventional refrigerant systems.
Innovation Solution
Incorporating an intercooler and liquid/vapor injection between compression stages, with the intercooler positioned to receive ambient airflow, and allowing selective activation of these components based on environmental and thermal conditions to optimize system performance, reducing discharge temperatures and enhancing efficiency and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an intercooler and liquid/vapor injection are provided between compression stages, then discharge temperature is reduced and system reliability is improved, but device complexity and additional components are required
Solution Approach 1:
The intercooler is merged with the heat rejecting heat exchanger by positioning it in the path of ambient airflow that already passes over the heat rejecting heat exchanger. This allows the same airflow to serve dual cooling functions, eliminating the need for a separate dedicated intercooler structure and reducing overall device complexity.
Solution Approach 2:
The ambient airflow path is made multi-functional by routing it to cool both the heat rejecting heat exchanger and the intercooler. This universal airflow approach allows a single cooling mechanism to serve multiple components, reducing the need for additional fans or pumps that would otherwise be required for the intercooler.
2Temperature
If an intercooler is provided between compression stages, then discharge temperature is reduced, but additional components and circuitry are required
Solution Approach 1:
The intercooler is designed to be self-cooling by utilizing the ambient airflow that already exists in the system for the heat rejecting heat exchanger. The intercooler passively receives cooling from this airflow without requiring its own dedicated fan, pump, or active cooling circuitry, thereby reducing additional components while still achieving discharge temperature reduction.
3Reliability
If liquid/vapor injection is provided, then discharge temperature is reduced and operational envelope is extended, but system complexity increases
Solution Approach 1:
The liquid/vapor injection system is merged with the existing refrigerant circulation path by injecting refrigerant at the compression stage inlet. This integration allows the injection function to be added to the existing system architecture rather than requiring a completely separate injection system, thereby extending the operational envelope while minimizing the increase in system complexity.
4Productivity
If CO2 refrigerant is used in transcritical cycle, then system capacity is enhanced, but discharge temperature becomes extremely high
Solution Approach 1:
The intercooler is positioned to cool the refrigerant between the lower and upper compression stages, performing preliminary cooling action before the refrigerant enters the upper stage. This preliminary cooling prevents the discharge temperature from becoming extremely high while maintaining the high system capacity benefits of CO2 transcritical cycle operation.
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 solution reduces compressor discharge temperatures, increases system capacity and efficiency, extends the operational envelope, and allows for independent adjustment of discharge pressure, thereby improving refrigerant system performance and reliability, especially in transcritical cycles.
Implementation Method 1
The intercooler is preferably positioned to be subjected to an airflow passing over a heat rejecting heat exchanger
Implementation Method 2
an outdoor fan that passes air over the heat rejecting heat exchanger may also provide cooling for the intercooler
Implementation Method 3
refrigerant leaving a heat rejecting heat exchanger is partially expanded in an auxiliary expansion device to an intermediate pressure and temperature and routed to a point between the compression stages where it is mixed with the refrigerant partially compressed in a lower compression stage
Implementation Method 4
at least a portion of refrigerant leaving a heat rejecting heat exchanger is partially expanded in an auxiliary expansion device to an intermediate pressure and temperature
Implementation Method 5
two separate compression members or two separate compressor units are disposed in series
Data Source
AI summary
A refrigerant system is provided with at least two sequential stages of compression. An intercooler is positioned intermediate the two stages. The refrigerant flowing through the intercooler is cooled by a secondary fluid such as ambient air. A vapor/liquid injection function is also provided for the refrigerant system. The intercooler function and the vapor/liquid injection function are selectively activated on demand depending on environmental conditions and thermal load in a conditioned space. This invention is particularly important for the CO2 refrigerant systems operating in the transcritical cycle.