Transport Refrigeration Defrost Control for Pressure-Balanced CO2 Cycles
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Refrigerant vapor compression systems in transport refrigeration face challenges in efficiently managing defrost operations, particularly in high-pressure systems, leading to potential refrigerant trapping and pressure imbalances that can cause system malfunctions and safety issues.
Innovation Solution
The system employs a method to control defrost operations by adjusting expansion valves and using heaters to manage pressure within the refrigerant vapor compression system, ensuring safe operation by preventing refrigerant flow into the compressor and maintaining balanced pressures, thereby reducing the risk of refrigerant trapping and pressure relief valve activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional defrost operations are used in high-pressure refrigerant vapor compression systems, then the heat absorption heat exchanger can be defrosted, but refrigerant may become trapped and pressure imbalances may occur leading to system malfunctions
Solution Approach 1:
The patent implements dynamic control of expansion valves during defrost operations, adjusting valve positions in real-time based on system pressure conditions. The controller modulates the first expansion valve to remain slightly open and the second expansion valve to be substantially open, creating dynamic pressure balance that prevents refrigerant trapping while maintaining safe operating pressures throughout the defrost cycle.
Solution Approach 2:
The system employs pressure sensing and controller-based feedback mechanisms to monitor system pressure during defrost operations. The controller receives pressure information and adjusts expansion valve positions accordingly, creating a closed-loop control system that maintains pressure balance and prevents harmful pressure imbalances that could lead to malfunctions or safety issues.
2Reliability
If expansion valves are closed during defrost mode to isolate the heat absorption heat exchanger, then defrosting can be effective, but refrigerant flow is restricted causing pressure buildup and potential safety issues
Solution Approach 1:
The patent applies local quality by differentiating the control strategy for different expansion valves based on their specific functions. The first expansion valve is kept slightly open to maintain pressure balance and allow controlled refrigerant flow, while the second expansion valve is kept substantially open to prevent pressure buildup. This localized differentiation of valve control states enables effective defrosting without harmful pressure accumulation.
Solution Approach 2:
The first expansion valve serves as an intermediary element between the high-pressure and low-pressure sides of the system during defrost operations. By maintaining a slight opening, it acts as a pressure balancing mechanism that allows controlled refrigerant flow to prevent pressure buildup while still enabling the heat absorption heat exchanger to be effectively isolated for defrosting.
3Adaptability or versatility
If the system operates in transcritical mode with carbon dioxide refrigerant, then environmental performance is improved, but defrost operations become more complex due to high-pressure conditions
Solution Approach 1:
The patent implements a universal defrost control strategy that works effectively for both subcritical and transcritical operating modes. The same controller logic and expansion valve control methodology apply regardless of whether the system is operating with conventional refrigerants or carbon dioxide in transcritical mode, simplifying the overall system design despite the environmental benefits of using CO2 refrigerant.
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 compressor reliability, reduces the likelihood of refrigerant trapping, and ensures safe operation during defrost modes by maintaining balanced pressures and preventing excessive pressure buildup, particularly in high-pressure transcritical cycles.
Implementation Method 1
energizing heaters corresponding to the heat absorption heat exchanger operable to defrost the heat absorption heat exchanger
Data Source
AI summary
A method for operating a defrost mode of a transport refrigerant vapor compression system includes initiating a defrost operation for the transport refrigerant vapor compression system by energizing heaters operatively coupled to a heat absorption heat exchanger operable to defrost the heat absorption heat exchanger. During the defrost operation, the method includes comparing the heat absorption heat exchanger pressure to the first predetermined limit; in response to the heat absorption heat exchanger pressure being less than the first predetermined limit, performing at least one operation to determine if the defrost operation should be exited; and in response to the heat absorption heat exchanger pressure being greater than the first predetermined limit, exiting the defrost operation.