Perturbation of expansion valve in vapor compression system

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Solution Overview

Problem

Vapor compression systems face issues with expansion valve control, leading to reduced capacity, potential liquid refrigerant compression, and increased wear on compressor components due to inadequate suction superheat management and high oil circulation ratios.

Innovation Solution

A controller is implemented to monitor and adjust compressor speed and fan speed based on compressor discharge superheat limits, reducing speed when superheat is below the limit and returning to demand levels when it exceeds, thereby perturbing the expansion valve to regain control of suction superheat.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the expansion valve is thermally controlled by temperature at the outlet of the evaporator to maintain desired superheat, then the superheat control should be improved, but the expansion valve does not control the suction superheat well and the primary accumulator overflows with liquid refrigerant

Engineering Contradiction:

Improvesuction superheat controlVSAvoidliquid refrigerant compression prevention

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The controller continuously monitors compressor discharge superheat and uses this feedback to dynamically adjust compressor speed and fan speed, creating a closed-loop control system that prevents liquid refrigerant compression by maintaining superheat within safe limits

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces the traditional thermal control mechanism of the expansion valve with an electronic control system that uses sensors and a controller to monitor and adjust operating parameters, substituting mechanical/thermal control with electronic feedback control

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If the expansion valve cannot control suction superheat properly, then liquid refrigerant compression occurs causing high stress on compression chamber components, but the system capacity is reduced by ~30%

Engineering Contradiction:

Improvecompression chamber component reliabilityVSAvoidsystem capacity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The controller dynamically adjusts compressor speed and fan speed based on real-time superheat measurements, allowing the system to adapt operating conditions to maintain reliability while optimizing capacity under varying load conditions

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes operating parameters (compressor speed, fan speed) in response to superheat conditions, enabling the system to maintain component reliability by preventing liquid compression while recovering system capacity through optimized operating points

Inventive Principle:

Principle #35Parameter changes

3Reliability

If high oil circulation ratio occurs due to inadequate superheat control, then less oil is maintained within the compressor shell leading to higher wear on rotor and bearing assembly, but the expansion valve cannot re-gain control of suction superheat

Engineering Contradiction:

Improverotor and bearing assembly reliabilityVSAvoidsuction superheat control recovery

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The continuous feedback loop monitors superheat and adjusts operating parameters to maintain proper oil circulation by preventing conditions that lead to high OCR, thereby protecting the rotor and bearing assembly while maintaining expansion valve control authority

Inventive Principle:

Principle #23Feedback

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 solution effectively maintains expansion valve control, reducing capacity loss, wear on compressor components, and enhancing system reliability by ensuring proper superheat management and oil circulation.

Implementation Method 1

a first fan configured to direct air over the first heat exchanger

Methodology Applied

Scientific EffectForced Convection: Forced Convection

Implementation Method 2

The expansion valve may be thermally controlled by temperature at the outlet of the evaporator to maintain a desired degree of superheat

Methodology Applied

Scientific EffectThermal control:

Implementation Method 3

Vapor compression systems typically include an expansion valve between a condenser and an evaporator

Methodology Applied

Scientific EffectCompression: Compression

Data Source

PatentUS10823474B2Perturbation of expansion valve in vapor compression system

Publication Date: 2020.11.03 CARRIER CORP

AI summary

A vapor compression system includes a compressor, a first heat exchanger, an expansion valve and a second heat exchanger arranged serial refrigerant flow path; a first fan configured to direct air over the first heat exchanger; a controller coupled to the first fan and the compressor, the controller configured to: set a compressor discharge superheat limit; determine a compressor discharge superheat; compare the compressor discharge superheat to the compressor discharge superheat limit; and when the compressor discharge superheat is less than the compressor discharge superheat limit, the controller reducing at least one of a compressor speed and a first fan speed.