Evaporator Refrigerant Control During Sensor Failure

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Solution Overview

Problem

Existing vapor compression systems, such as refrigeration and air conditioning systems, face inefficiencies and risks of liquid refrigerant damage when sensors used for controlling refrigerant supply become unavailable or unreliable, preventing them from operating efficiently and adapting to changes in refrigeration load.

Innovation Solution

A method for controlling refrigerant supply to an evaporator in a vapor compression system by calculating a reference temperature based on previous measurements when sensors malfunction, allowing the system to maintain efficient operation and adjust to changes in refrigeration load by controlling the expansion valve's opening degree based on the calculated reference temperature.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the expansion valve opening degree is reduced to a fixed percentage of the average opening degree during contingency mode, then liquid refrigerant is prevented from passing through the evaporator, but the system cannot adapt to changes in refrigeration load and operates inefficiently

Engineering Contradiction:

Improveprevention of liquid refrigerant damageVSAvoidsystem efficiency and load adaptation

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The expansion valve opening degree is changed from a static fixed percentage to a dynamic value that continuously adjusts based on the difference between actual and reference refrigerant temperatures. This allows the system to adapt to changing refrigeration loads while maintaining safety margins against liquid refrigerant damage.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

A feedback control mechanism is implemented where the actual refrigerant temperature at the evaporator outlet is continuously measured and compared against a reference temperature. The expansion valve opening degree is adjusted based on this temperature difference, creating a closed-loop control system that maintains both safety and efficiency.

Inventive Principle:

Principle #23Feedback

2Adaptability or versatility

If the expansion valve opening degree is controlled based on air temperature measurements, then the refrigeration load can be managed, but the system becomes vulnerable when temperature sensors are unavailable or unreliable

Engineering Contradiction:

Improverefrigeration load managementVSAvoidsensor dependency

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

When primary temperature sensors fail, the system uses an intermediary approach by calculating a reference temperature based on historical data and using this calculated value as a substitute for the missing sensor input. This allows the control system to continue functioning with reduced sensor availability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system prepares for sensor failure by establishing a reference temperature from historical measurements before the sensor actually fails. This pre-calculated reference serves as a cushion that allows the system to maintain operation even when sensors become unavailable.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If the expansion valve opening degree is maintained at a reduced fixed value during sensor failure, then system safety is ensured, but energy efficiency is compromised

Engineering Contradiction:

Improvesystem safetyVSAvoidenergy efficiency

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The system dynamically changes the opening degree parameter of the expansion valve based on the temperature difference between actual and reference values. This allows the system to operate at optimal efficiency points while maintaining safety margins, rather than being locked into a conservatively reduced fixed opening degree.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS10663200B2Method for controlling a supply of refrigerant to an evaporator in contingency mode

Publication Date: 2020.05.26 DANFOSS AS

AI summary

A method for controlling a supply of refrigerant to an evaporator of a vapour compression system, such as a refrigeration system, an air condition system or a heat pump. During normal operation, the opening degree of the expansion valve is controlled on the basis of an air temperature, Tair, of air flowing across the evaporator and/or on the basis of superheat of refrigerant leaving the evaporator. If at least one sensor used for obtaining Tair or the superheat is malfunctioning, operation of the vapour compression system is switched to a contingency mode. A reference temperature, Tout, ref, is calculated, based on previously obtained values of a temperature, Tout, of refrigerant leaving the evaporator, during a predefined previous time interval, and subsequently the opening degree of the expansion valve is controlled on the basis of the obtained temperature, Tout, in order to reach the calculated reference temperature, Tout, ref.