Supply Air Temperature Control for Refrigerated Containers
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Solution Overview
Problem
Refrigerated transport containers struggle to quickly reach desired temperature ranges when loaded with warm products, leading to quality loss due to high and low temperatures, as traditional temperature control methods rely on inadequate indicators and fail to efficiently manage supply and return air temperatures in non-steady state conditions.
Innovation Solution
A method and system for controlling supply air temperature in refrigerated transport containers, where the temperature is temporarily reduced below the set point during an initial period and then increased to the set point over a second period, using a master-slave controller to adjust the supply air temperature set point based on measured return and supply air temperatures, ensuring product temperatures reach the desired range quickly while minimizing quality loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If supply air temperature is controlled to set point from the beginning, then product temperatures will not fall below desired range, but temperature pull-down is slow and quality loss from high temperatures occurs
Solution Approach 1:
The control system performs preliminary action by temporarily reducing supply air temperature below the set point during an initial period when the transport volume is still warm. This preliminary cooling action accelerates the temperature pull-down process before transitioning to normal set point control, thereby resolving the contradiction between fast cooling and preventing over-cooling.
Solution Approach 2:
The invention applies dynamics by making the supply air temperature control strategy adaptive and time-dependent. The system dynamically switches between two control modes: aggressive cooling mode (supply temperature below set point) during the initial period, and normal control mode (supply temperature at set point) during the second period. This dynamic adjustment optimizes both cooling speed and temperature maintenance.
2Productivity
If supply air temperature is reduced below set point to accelerate cooling, then temperature pull-down speed increases, but product temperatures may fall below desired range causing chilling injury
Solution Approach 1:
The control system implements periodic action by dividing the cooling process into distinct time periods with different control strategies. During the first period, aggressive cooling below set point is applied to accelerate pull-down. During the second period, normal set point control is applied to maintain temperatures and prevent chilling injury. This periodic switching resolves the contradiction between cooling speed and product safety.
Solution Approach 2:
The system performs preliminary aggressive cooling action during the first period when products are still warm and less susceptible to chilling injury. After this preliminary cooling phase establishes the temperature trend, the system transitions to protective set point control in the second period, preventing temperatures from falling below the desired range and avoiding chilling injury.
3Device complexity
If traditional temperature control is used with inadequate indicators, then device complexity is low, but temperature control precision is insufficient in non-steady state conditions
Solution Approach 1:
The invention enhances temperature control accuracy by implementing a dynamic control strategy that adapts to non-steady state conditions. The system uses time-based control logic that recognizes different operational phases (initial warm period vs. cooling period) and applies appropriate control actions for each phase, thereby achieving precise temperature management without requiring complex additional hardware.
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 accelerates the temperature pull-down in the transport volume, reducing quality loss from high temperatures and preventing chilling or freezing injuries by gradually adjusting the supply air temperature, ensuring product temperatures remain within the desired range without falling below it.
Implementation Method 1
One typical type of a cooling unit or refrigeration unit used in refrigerated transport containers is based on the so-called vapour compression refrigeration cycle. This cycle comprises at least a compressor, a condenser, an expansion device, an evaporator and a capacity regulating device.
Implementation Method 2
The low pressure refrigerant then flows to the evaporator where the refrigerant evaporates while extracting the required heat from the refrigerated transport container.
Implementation Method 3
one or more fans providing an air flow through the cooling space
Data Source
AI summary
Temperature is controlled in a refrigerated transport container comprising a transport volume, a control unit, a cooling space, one or more fans providing air flow through the cooling space, where air passing through the cooling space passes a return air temperature sensor, a cooling unit, and a supply air temperature sensor. Supply air temperature (Tsup) is controlled to bring temperatures in the transport volume within a desired temperature range around a first temperature set point (Tset). The supply air temperature (Tsup) or a time-averaged function thereof is controlled to reach a temperature below the set point (Tset) during a first limited time period; and the supply air temperature (Tsup) is increased during a second limited time period following said first time period, so that the supply air temperature (Tsup) or a time-averaged function thereof at the end of said second time period is within said desired temperature range.