Low-Ambient Refrigerator Cavity Control by Compressor Duty Cycle
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Solution Overview
Problem
In refrigeration appliances, low ambient temperatures can cause the freezer compartment to warm up due to the cooling system not turning on, leading to undesired thawing, and simultaneously, the fresh-food compartment may cool down below freezing due to air leakage, necessitating a more effective temperature control method.
Innovation Solution
A microprocessor-based control system that calculates the compressor duty cycle to execute a low ambient mode control algorithm, which includes strategies such as keeping the compressor and evaporator fan on for specific periods to maintain freezer temperature and using a heating element to prevent fresh-food compartment freezing, without requiring an external heating element, ambient temperature sensor, or electronic damper.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the cooling system uses the fresh-food compartment temperature to determine when to turn ON or OFF, then the fresh-food compartment temperature control is simple, but in low ambient temperatures the cooling system might never turn ON causing the freezer compartment to warm up
Solution Approach 1:
The control system continuously monitors both fresh-food and freezer compartment temperatures and uses this feedback to intelligently control the cooling system operation. The microprocessor adjusts compressor and evaporator fan operation based on real-time temperature readings from both compartments, ensuring reliable freezer temperature maintenance while avoiding unnecessary complexity.
Solution Approach 2:
The system changes operational parameters (compressor duty cycle, evaporator fan operation) based on ambient temperature conditions. In low ambient temperatures, the system modifies the control logic to prevent the compressor from shutting off completely, thereby maintaining freezer temperature reliability without requiring a fundamentally different control architecture.
2Reliability
If the cooling system operates continuously to maintain freezer temperature in low ambient conditions, then the freezer temperature is maintained, but the fresh-food compartment may cool down below freezing due to air leakage
Solution Approach 1:
The control system applies different control strategies to different compartments. The evaporator fan is controlled to provide targeted cooling to the freezer compartment while limiting excessive cooling in the fresh-food compartment. The system adjusts air circulation patterns locally to prevent fresh-food items from freezing while maintaining freezer temperature.
Solution Approach 2:
The system dynamically adjusts the evaporator fan duty cycle and compressor operation based on real-time temperature conditions in both compartments. When the fresh-food compartment approaches freezing temperature, the system reduces cooling intensity or temporarily suspends evaporator fan operation to allow the fresh-food compartment to warm back up, preventing freezing while maintaining overall system reliability.
3Measurement precision
If additional components like external heating elements, ambient temperature sensors, or electronic dampers are added to control temperature in low ambient conditions, then temperature control accuracy improves, but device complexity and cost increase
Solution Approach 1:
The microprocessor-based control system performs multiple functions using existing components: it monitors both compartment temperatures, controls the compressor operation, manages the evaporator fan duty cycle, and adjusts cooling intensity based on ambient conditions. This multi-functional approach achieves accurate temperature control without requiring additional specialized components like external heating elements or electronic dampers.
Solution Approach 2:
The system uses the temperature data from the existing fresh-food compartment sensor to infer ambient temperature conditions and automatically adjusts its control strategy accordingly. The control algorithm self-regulates the compressor and evaporator fan operation based on the interaction between the two compartments, eliminating the need for separate ambient temperature sensors or manual intervention.
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 freezer thaw and fresh-food compartment freezing, maintaining optimal temperatures without additional costly components, ensuring reliable operation in low ambient conditions.
Implementation Method 1
using a heating element to prevent fresh-food compartment freezing
Implementation Method 2
cold air from the freezer compartment might cause the fresh-food compartment (and items stored therein) to cool down below the freezing point
Data Source
Figure 1
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Figure 4
AI summary
A method of controlling the temperature in cavities of a refrigerator (10) cooled by a refrigeration circuit having a compressor (18) and an evaporator (32) includes the steps of: monitoring the duty cycle of the compressor (18); determining whether the duty cycle is below a threshold; determining whether the temperature of the evaporator (32) is above a threshold; and if the duty cycle is below the threshold and if the evaporator temperature is above a threshold, activating the refrigeration circuit to start cooling of at least one of the refrigerator cavities. A refrigeration appliance (10) with a controller that activates the refrigeration circuit based on the monitored duty cycle of the compressor (18) and the evaporator temperature is also provided.