Control of pull-down in refrigeration systems
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Refrigeration systems in cargo containers consume excessive energy during the pull-down phase to achieve target temperatures, leading to inefficient cooling and increased operational costs.
Innovation Solution
Operating the evaporator fan at reduced speed during the pull-down phase, while maintaining constant compressor power, increases the temperature difference between return and supply air, reducing energy consumption and accelerating the cooling process without degrading system performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the evaporator fan is operated at high speed during pull-down, then the refrigeration effect is maximized and cargo is refrigerated quickly, but the energy consumption increases significantly
Solution Approach 1:
The evaporator fan speed is dynamically adjusted based on the refrigeration stage: high speed during pull-down to maximize cooling effect, then automatically reduced to low speed when target temperature is reached. This dynamic adjustment resolves the contradiction by matching fan speed to actual cooling needs, achieving fast refrigeration when required while minimizing energy consumption during maintenance phase.
Solution Approach 2:
The system changes the operating parameters of the evaporator fan from high speed to low speed based on temperature conditions. During pull-down, high fan speed provides maximum air circulation and heat exchange; when target temperature is reached, the parameter changes to low speed, maintaining adequate air flow while dramatically reducing energy consumption and friction heat generation.
2Productivity
If the evaporator fan operates at high speed, then air circulation is maximized for efficient heat exchange, but friction heat generated in the container increases
Solution Approach 1:
The system applies partial action by operating the evaporator fan at high speed only during the pull-down phase when maximum cooling is needed, rather than continuously. Once the target temperature is reached, the fan speed is reduced to low level, providing just enough air circulation for heat exchange while minimizing friction heat generation. This partial application of high speed action resolves the contradiction between heat exchange efficiency and friction heat.
3Power
If the compressor operates at full capacity during pull-down, then the refrigeration effect is maximized, but the pull-down period still extends longer than desired
Solution Approach 1:
The system maintains continuous useful action by keeping the compressor operating at full capacity throughout the pull-down phase without interruption. Combined with high-speed evaporator fan operation, this ensures maximum refrigeration power is continuously applied to the cargo, achieving the shortest possible pull-down duration while maximizing refrigeration effectiveness.
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 significantly saves energy and shortens the pull-down period, maintaining the set-point temperature effectively and reducing energy consumption by optimizing air flow and refrigerant circulation.
Implementation Method 1
The extracted return air is blown past the evaporator to refrigerate the air, and the refrigerated supply air is blown as into the container where it circulates and exchanges heat with the cargo and/or with the walls of the container
Implementation Method 2
The vapor-compression cycle is used in most household refrigerators as well as in many large commercial and industrial refrigeration systems
Implementation Method 3
The extracted return air is blown past the evaporator to refrigerate the air
Implementation Method 4
The vapor-compression cycle is used in most household refrigerators as well as in many large commercial and industrial refrigeration systems
Data Source
Figure 1~2
Figure 3
AI summary
A method for operating a refrigeration system (100) for a container to pull down the temperature of cargo from ambient to a predetermined set-point temperature, and a system employing the method. The method includes operating a compressor (110) at a first power to compress a refrigerant and direct the refrigerant through a condenser (120) and an evaporator (140) of the refrigeration system, initially operating an evaporator fan (150) at a first speed to supply refrigerated supply air from the evaporator to the cargo within the container, sensing the temperature of the supply air, comparing the temperature of the supply air with a predetermined set-point temperature, and increasing the speed of the evaporator fan (150) to a second speed faster than the first when the temperature of the supply air is lower than the predetermined set-point temperature to maintain the temperature of the supply air at the predetermined set-point temperature.