Refrigerated Trailer Freeze Protection Using Return Air Control
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Solution Overview
Problem
Current temperature control systems for refrigerated trailers struggle to prevent cargo from freezing while maintaining the set point temperature, often requiring complex fluid control systems and algorithms that interfere with each other, leading to software complexity and inefficiency.
Innovation Solution
A method and system that control the return air temperature by switching between cooling and heating modes, using timers and counters to adjust the target temperature gradually, preventing discharge air from dropping below freezing and maintaining the set point temperature by incrementing or decrementing the target temperature based on mode transitions and durations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If discharge air temperature is reduced to maintain set point temperature, then cooling efficiency is improved, but cargo near discharge air vent freezes
Solution Approach 1:
The patent segments the temperature control function into two independent control loops: one controlling return air temperature to maintain set point, and another controlling discharge air temperature to prevent freezing. This segmentation allows each control loop to optimize its function without interfering with the other, resolving the contradiction between maintaining set point temperature and preventing cargo freezing.
Solution Approach 2:
The patent introduces an intermediary null band temperature range between the set point temperature and freezing temperature. The discharge air temperature controller maintains discharge air temperature above this null band, creating a buffer zone that prevents cargo freezing while allowing the return air controller to maintain the set point temperature. This intermediary temperature band mediates between the conflicting requirements.
2Reliability
If complex fluid control systems and combined algorithms are used to prevent cargo freezing, then freeze protection is improved, but control system complexity increases
Solution Approach 1:
The patent divides the temperature control system into two separate, independent control loops: a return air temperature controller and a discharge air temperature controller. Each controller operates independently with its own control algorithm, eliminating the need for complex combined algorithms. This segmentation simplifies the overall control system architecture while providing reliable freeze protection through the specialized function of each controller.
Solution Approach 2:
The patent makes the temperature control system multi-functional by enabling the same refrigeration unit to operate in different modes (cooling and heating) based on temperature conditions. The controller automatically switches between cooling mode to maintain set point temperature and heating mode to prevent discharge air temperature from dropping too low, providing both temperature maintenance and freeze protection functions through a single integrated system.
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
Effectively prevents top freeze and maintains the cargo temperature close to the set point without requiring complex control systems, ensuring efficient and stable temperature regulation in refrigerated spaces.
Implementation Method 1
cooling the refrigerated space in a cool mode
Implementation Method 2
heating the refrigerated space in a heat mode
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A method for freeze protection for a temperature control system, and a temperature control system for controlling the temperature of a temperature-controlled space (14) at a set point temperature. The method includes monitoring a discharge air (54) temperature, monitoring a return air (50) temperature, setting a target temperature to equal the set point temperature, controlling the return air temperature at the target temperature, and adjusting the target temperature based on the return air temperature when the discharge air temperature drops to one of at or below freezing.