Return Air Grid Defrost Control in Refrigerated Containers
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Solution Overview
Problem
Refrigerated transport containers face challenges in preventing frost and ice buildup on components above and upstream the evaporator, particularly on the return air grid, and in the supply air ducts, leading to air circulation blockages and increased costs due to the need for repacking sensitive cargo.
Innovation Solution
A method to decide when to terminate a defrosting cycle by monitoring indicators of frost and ice buildup on the return air grid, prolonging the defrosting cycle until all frost and ice have melted, ensuring the entire cooling space remains free of ice and frost without requiring hardware modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the defrosting cycle is terminated early to maintain cooling efficiency, then energy consumption is reduced, but frost and ice buildup on the return air grid occurs leading to air circulation blockages
Solution Approach 1:
The system uses temperature sensors to continuously monitor the return air grid temperature and provides feedback to the controller. When the sensor detects that the return air grid temperature approaches the freezing point, the controller extends the defrosting cycle accordingly, creating a closed-loop control system that balances energy consumption with reliable air circulation.
Solution Approach 2:
The defrosting cycle is extended in advance based on predicted frost accumulation conditions. The controller proactively prolongs defrosting before complete blockage occurs, using temperature trends and environmental conditions to anticipate when frost will form on the return air grid, preventing air circulation issues before they arise.
2Reliability
If the defrosting cycle is prolonged to prevent frost and ice buildup on the return air grid, then air circulation reliability is improved, but energy consumption increases
Solution Approach 1:
The defrosting cycle duration is made dynamic rather than fixed. The controller continuously adjusts the defrosting cycle length based on real-time temperature sensor feedback, environmental conditions, and frost accumulation rates. This dynamic adjustment ensures the minimum necessary defrosting time is used to maintain air circulation reliability while minimizing energy consumption.
Solution Approach 2:
The system changes the temperature threshold parameters that trigger defrosting cycle extension. By adjusting these parameters based on cargo sensitivity, environmental conditions, and operational history, the system optimizes the balance between air circulation reliability and energy consumption, extending defrosting only when necessary to prevent blockages.
3Productivity
If traditional defrosting termination methods are used, then the cooling unit operates efficiently, but frost buildup on components above the evaporator is not prevented
Solution Approach 1:
The monitoring system is extended from the traditional evaporator level to include the return air grid and other components above the evaporator in the vertical dimension. Temperature sensors are positioned at multiple heights to detect frost accumulation trends, allowing the defrosting cycle to be extended to prevent frost buildup on upper components while maintaining cooling efficiency at the evaporator level.
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 prevents air circulation blockages and reduces the need for repacking sensitive cargo, maintaining the integrity of temperature-sensitive goods during transportation without additional hardware costs or installation, ensuring efficient operation of refrigerated transport containers.
Implementation Method 1
The evaporator is the part of the refrigeration system in which the refrigerant absorbs heat from the transport volume and thereby cools air forced over or through the evaporator
Implementation Method 2
moist and water carried by the air passing over or through the evaporator may settle on the cold surfaces of the evaporator thereby initiating frost and/or ice build-up
Implementation Method 3
means for actively heating said evaporator (16) during defrosting cycles
Implementation Method 4
A flow of warm air melts ice much slower than frost
Data Source
AI summary
The present invention relates to a method, device and computer program for terminating a defrosting cycle within a refrigerated transport container. The container may include: a transport volume, a cooling unit comprising an evaporator arranged in a cooling space, a return air grid arranged to separate said cooling space from said transport volume, means for sensing temperature indicative of the return air temperature of air returning to said cooling space from said transport volume or the temperature of the return air grid, means for actively heating said evaporator during defrosting cycles, and a processor configured for controlling the duration of said defrosting cycles. The method includes: establishing an indicator(s) indicative of frost and/or ice build-up on said return air grid, and terminating a defrosting cycle when an indicator(s) of frost and/or ice build-up on said return air grid indicates that said return air grid is free of frost and/or ice.