Compressor Cycling Control to Prevent Evaporator Ice Build-Up
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Solution Overview
Problem
Ice formation on and below evaporator coils of intermittently operated cooling units in refrigerated storage spaces, particularly in refrigerated transport containers, leads to efficiency decreases and potential blockages, as existing defrost cycles often require interruptions in cooling and may not effectively manage ice accumulation.
Innovation Solution
The compressor cycling pattern is altered to reduce melting-refreezing cycles and maintain a supply air temperature slightly above 0°C, using existing temperature sensors to prevent ice formation by extending the active state when temperatures approach freezing, ensuring proper condensate drainage and unit functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the compressor is intermittently operated to avoid energy-inefficient part-load operation, then energy efficiency is improved, but ice formation occurs on the evaporator surface
Solution Approach 1:
The control system performs preliminary action by extending the compressor active state before ice formation becomes problematic. When the supply air temperature approaches 0°C during intermittent operation, the controller proactively extends the active state to prevent the evaporator surface temperature from dropping below freezing, thereby preventing ice formation before it occurs.
Solution Approach 2:
The system uses feedback from temperature sensors monitoring the supply air temperature to dynamically adjust the compressor cycling pattern. When the supply air temperature approaches the critical 0°C threshold, the feedback signal triggers an extension of the active state, creating a closed-loop control system that prevents ice formation while maintaining intermittent operation for energy efficiency.
2Object-affected harmful factors
If defrost cycles are implemented to remove frost, then frost accumulation is reduced, but cooling process is interrupted
Solution Approach 1:
The system applies preliminary anti-action by preventing ice formation in the first place through extended active state operation when temperatures approach freezing. This preventive approach eliminates the need for subsequent defrost cycles, thereby maintaining continuous cooling operation and avoiding productivity interruptions.
Solution Approach 2:
The invention converts the potentially harmful effect of extended compressor operation (increased energy consumption) into a benefit by preventing ice formation. The extended active state, which might seem counterproductive, actually prevents the need for defrost cycles and maintains continuous cooling, ultimately improving overall system performance.
3Productivity
If the supply air temperature is maintained below 0°C for effective cooling, then cooling performance is improved, but ice formation risk increases
Solution Approach 1:
The system dynamically adjusts the supply air temperature based on real-time conditions. During active compressor states, the temperature is maintained below 0°C for effective cooling performance. However, when the temperature approaches 0°C during intermittent operation, the system dynamically extends the active state to prevent ice formation, creating a flexible temperature control strategy that balances cooling performance with ice prevention.
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 effectively reduces ice formation, maintaining a clean evaporator surface and ensuring airflow, while avoiding interruptions in cooling and minimizing the risk of freezing damage to perishable goods.
Implementation Method 1
The low pressure refrigerant then flows to the evaporator, situated in the cooling space, where the refrigerant evaporates while extracting the required heat from the refrigerated storage space
Implementation Method 2
The condenser ejects its heat to a medium outside the refrigerated transport container while condensing the refrigerant vapour
Implementation Method 3
Frost is formed when solid surfaces are cooled to below the so-called dew point of the adjacent air as well as below the freezing point of water
Implementation Method 4
The compressor sucks refrigerant vapour from the evaporator and compresses the refrigerant vapour which subsequently flows to the condenser at high pressure
Data Source
AI summary
Disclosed is a system for and a method of reducing and/or avoiding ice formation inside a cooling space (41) of a refrigerated transport container (1) comprising at least a cooling unit (40) and an evaporator (16) located in the cooling space (41), where the cooling unit (40) comprises at least an intermittently operated compressor (6) operated between a first active state and a second less active state, and wherein the method comprises: reducing and/or avoiding ice formation inside the cooling space (41), when the system is operated at a temperature setpoint where a potential risk of ice build-up on the external surface of the evaporator exists, by altering a cycling of the compressor (6) between the first active state and the second less active state such that the number of melting-refreezing cycles at an external surface of the evaporator is reduced. In this way, ice formation in the cooling space is reduced and/or avoided, which helps to maintain a clean external evaporator surface area and open condensate collection guide(s) (20). This in turn helps to ensure the proper drain off of melting water to outside the container and the persistent proper functioning of the cooling unit.