Ejector-Based Refrigerant Cycle for Efficient Part-Load Operation

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Solution Overview

Problem

Existing refrigerant cycles, such as air-to-water heat pumps, become oversized and inefficient at low-heat-load conditions, leading to frequent cycling, reduced system life, and increased energy bills, particularly in well-insulated homes, due to the inefficiencies in current hot-gas-bypass methods that degrade evaporator performance and require unnecessary compressor re-compression of refrigerant.

Innovation Solution

Incorporating an ejector with a primary nozzle connected to the compressor discharge and a suction nozzle connected to a secondary port of the evaporator, allowing for pre-compression of refrigerant vapor before the main compressor stage, thereby bypassing the condenser and reducing compressor load during part-load or low-heat-load operations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a variable speed compressor runs at minimum frequency to handle low-heat-load, then the heat pump can operate continuously, but the system becomes oversized and efficiency deteriorates

Engineering Contradiction:

Improvecontinuous operationVSAvoidenergy efficiency

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The compression process is segmented into two stages: a first compression stage using the ejector where high-pressure hot-gas pre-compresses the refrigerant vapour, and a second compression stage using the main compressor. This segmentation allows the main compressor to operate more efficiently by receiving pre-compressed vapour rather than handling the full compression load alone, thereby improving energy efficiency during continuous low-heat-load operation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The ejector performs preliminary compression of the refrigerant vapour before it enters the main compressor. By pre-compressing the vapour using the kinetic energy of the high-pressure hot-gas, the system reduces the work required by the main compressor, enabling efficient continuous operation at low-heat-load conditions.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If hot-gas-bypass method is used for load modulation, then the system can run at partial heat load, but evaporator thermal performance is downgraded due to increased refrigerant dryness

Engineering Contradiction:

Improvepartial heat load operationVSAvoidevaporator thermal performance

Core Design Contradiction:

Adaptability or versatilityVSProductivity

Solution Approach 1:

The ejector acts as an intermediary device between the high-pressure hot-gas and the evaporator outlet. Instead of directly mixing hot-gas with the evaporator outlet (which increases dryness and reduces performance), the ejector uses this hot-gas to drive a pre-compression process, thereby mediating the interaction in a way that maintains evaporator performance while enabling partial load operation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the conventional thermal mixing approach (hot-gas bypass directly into evaporator outlet) with a mechanical pre-compression approach using the ejector. This substitution transforms the harmful thermal effect (increased dryness) into a useful mechanical effect (pre-compression), allowing partial load operation without degrading evaporator performance.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If bypassed hot-gas is re-compressed by the compressor, then the refrigerant cycle is maintained, but compressor energy is wasted as the bypassed gas contributes nothing to heating efficiency

Engineering Contradiction:

Improverefrigerant cycle maintenanceVSAvoidcompressor energy waste

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent converts the previously harmful effect of bypassed hot-gas (which wasted compressor energy without contributing to heating) into a beneficial pre-compression stage. The high-pressure hot-gas that would have been merely recirculated is now used to drive the ejector and pre-compress the refrigerant vapour, transforming energy waste into useful work that improves overall system efficiency.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 configuration enhances efficiency by reducing compressor power consumption and preventing on-off cycling, maintaining heating capacity while optimizing refrigerant dryness and subcooling, thus improving overall system performance and energy efficiency at partial loads.

Implementation Method 1

an ejector which can use high-pressure hot-gas to pre-compress refrigerant vapour leaving from an evaporator as a first compression stage

Methodology Applied

Scientific EffectEjector effect: Injector

Implementation Method 2

passing this pre-compressed vapour to a main compressor for a second compressed stage

Methodology Applied

Scientific EffectCompression: Compression

Data Source

PatentEP3225939B1Refrigerant cycle with an ejector

Publication Date: 2022.11.09 MITSUBISHI ELECTRIC CORP

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AI summary

The present invention relates to a refrigerant cycle which can efficiently run at part-load and/or low-heat-load. The refrigerant cycle includes an ejector which can use high-pressure hot-gas to pre-compress refrigerant vapour leaving from an evaporator as a first compression stage before passing this pre-compressed vapour to a main compressor for a second compressed stage.