VRF System Artificial Load Circuit for Extra Low Load Operation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

HVAC systems, particularly Variable Refrigerant Flow (VRF) systems, face inefficiencies and inability to operate effectively in extra low load conditions due to limitations in compressor speed ranges, leading to inefficient operation and rapid power cycling.

Innovation Solution

A VRF system with a controller that manages refrigerant flow by using valves and expansion valves to create artificial loads, allowing the compressor to operate at its lowest speed setting while meeting demands below the compressor's operational range, and adjusting fan speeds and metering device positions to optimize refrigerant flow and heat transfer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the compressor operates at its lowest speed setting to improve energy efficiency, then energy consumption is reduced, but the system cannot meet cooling demands below the compressor's operational range

Engineering Contradiction:

Improvecompressor energy consumptionVSAvoidsystem adaptability to low load conditions

Core Design Contradiction:

Use of energy by moving objectVSAdaptability or versatility

Solution Approach 1:

The refrigerant flow path is segmented into multiple independent circuits with separate expansion valves and coils. This allows the system to divide the cooling load across different refrigerant streams, enabling the compressor to operate at minimum speed while still meeting total cooling demand through coordinated operation of multiple segments.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An artificial load circuit is introduced as an intermediary element. This circuit includes an expansion valve and coil that create a dummy cooling load, allowing the compressor to maintain minimum operation while the artificial load absorbs excess refrigerant capacity, effectively enabling operation below the compressor's natural operational range.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If the compressor speed is reduced to meet low cooling demand, then the system matches the cooling demand, but the compressor experiences rapid power cycling which reduces reliability

Engineering Contradiction:

Improvecooling demand matchingVSAvoidcompressor reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The system maintains continuous compressor operation at minimum speed by introducing an artificial cooling load through the second expansion valve and coil circuit. This artificial load ensures the compressor continuously processes refrigerant without shutting down, eliminating rapid power cycling and extending compressor life while still meeting actual cooling demands through the first circuit.

Inventive Principle:

Principle #20Continuity of useful action

3Adaptability or versatility

If multiple valves and expansion valves are added to create artificial loads and enable low load operation, then the system can operate in extra low load conditions, but the device complexity increases

Engineering Contradiction:

Improveoperation rangeVSAvoidsystem complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The additional valves and expansion devices serve multiple functions: they create artificial loads for low-speed operation, provide independent flow control paths, and enable the system to operate across a broader range of cooling demands. This multi-functionality justifies the added complexity by providing versatile operation capabilities that a single-circuit system cannot achieve.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

Enables efficient operation in both low and regular load conditions, providing flexible climate control and extending compressor life by preventing short cycling, thus ensuring reliable heating and cooling performance across a broader range of demands.

Implementation Method 1

a compressor operable to compress refrigerant

Methodology Applied

Scientific EffectCompression: Compression

Implementation Method 2

a first expansion valve coupled to the first coil, a second expansion valve further coupled to a third coil

Methodology Applied

Scientific EffectPressure drop: Pressure Drop

Implementation Method 3

a first valve coupled to the compressor and coupled to a first coil

Methodology Applied

Scientific EffectHeat transfer: Convection

Implementation Method 4

the first expansion valve to direct a first amount of the refrigerant from the first coil to the second coil

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS11092368B2Methods and systems for operating HVAC systems in low load conditions

Publication Date: 2021.08.17 LENNOX IND INC

AI summary

A system comprising a compressor, a first valve coupled to the compressor and coupled to a first coil, a first expansion valve coupled to the first coil, a second coil, and a second expansion valve. The second expansion valve coupled to a third coil, a second valve coupled to the compressor and the third coil. A controller operable to operate the first valve, the first expansion valve, the second expansion valve, and the second valve. The second coil is coupled to the compressor and the refrigerant flows from the second coil to the compressor.