Method and system for transport container refrigeration control
Solution Overview
Problem
Direct drive transport refrigeration systems face compressor damage and premature failure due to liquid flowback during hot gas defrost, and have non-optimal defrost timing, leading to compressor slugging issues.
Innovation Solution
A method and system that include a defrost cycle with a heat source, a pressure equalization valve in parallel with the compressor, and a liquid valve in series between the condenser and evaporator, controlled by a controller to manage compressor restart and avoid liquid slugging, involving a specific sequence of initiating compressor speed, opening and closing valves to equalize pressure and allow liquid flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If hot gas defrost technology with shunted condenser and expansion valve is used, then defrosting function is achieved, but compressor liquid flowback and slugging occur
Solution Approach 1:
A liquid bypass valve is introduced as an intermediary component between the condenser and evaporator. This valve allows liquid refrigerant to bypass the evaporator during defrost cycles, preventing liquid flowback into the compressor while maintaining the hot gas defrost function. The bypass valve acts as a mediator that separates the defrost function from the cooling function, allowing independent control of refrigerant flow paths.
Solution Approach 2:
The system dynamically switches between different refrigerant flow configurations based on operational mode. During cooling cycles, the bypass valve closes to allow normal refrigerant flow through the evaporator. During defrost cycles, the bypass valve opens to redirect liquid refrigerant away from the evaporator, preventing slugging. This dynamic adjustment of flow paths resolves the contradiction between achieving defrost and preventing compressor damage.
2Device complexity
If direct drive transport refrigeration system is used, then system simplicity is achieved, but compressor protection against liquid flowback is insufficient
Solution Approach 1:
The liquid bypass valve serves as a minimal additional component that provides comprehensive compressor protection. By placing this single intermediary valve in the liquid line between condenser and evaporator, the system gains automatic protection against liquid flowback during defrost cycles without requiring complex valve assemblies or multiple protective devices.
Solution Approach 2:
The bypass valve is integrated into the existing refrigeration circuit and operates automatically based on system conditions. During defrost cycles when liquid refrigerant would normally flow into the evaporator and potentially slug the compressor, the bypass valve automatically opens to redirect the liquid flow, providing self-service protection without requiring external intervention or complex control systems.
3Productivity
If compressor is initiated immediately after defrost cycle, then system productivity is improved, but liquid slugging risk increases
Solution Approach 1:
The bypass valve opens in advance before the compressor is initiated after a defrost cycle. This preliminary action ensures that the liquid refrigerant path is already diverted away from the evaporator before the compressor starts, preventing any risk of liquid slugging. The valve remains open for a predetermined period or until specific conditions are met, ensuring safe compressor restart while minimizing downtime.
Solution Approach 2:
The control system monitors system conditions and uses feedback to determine when to close the bypass valve and restart the compressor. After the defrost cycle completes, the system waits for appropriate conditions (such as pressure equalization or temperature thresholds) before closing the bypass valve and initiating the compressor, ensuring that liquid slugging is prevented while maintaining optimal productivity.
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 limits compressor liquid flow and optimizes defrost timing, preventing compressor slugging and extending its lifespan by controlling the restart process and managing liquid flow effectively.
Implementation Method 1
performing a defrost cycle on the refrigeration system by activating a heat source
Implementation Method 2
opening a pressure equalization valve in parallel with the compressor in response to the initiating
Data Source
AI summary
A method of refrigeration control through a refrigeration system of a refrigerated transport container includes performing a defrost cycle on the refrigeration system by activating a heat source; and restarting the refrigeration system after the defrost cycle has completed, wherein restarting the refrigeration system includes performing a liquid slugging avoidance process including: initiating a compressor of the refrigeration system at a speed; opening a pressure equalization valve in parallel with the compressor in response to the initiating; opening a liquid valve in series between a condenser and an evaporator after opening of the pressure equalization valve; and closing the pressure equalization valve after a period of time.