Compressor Hot Gas Bypass for Stable Low-Load Refrigeration

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Solution Overview

Problem

Conventional refrigeration systems experience compressor damage and operational disruptions due to frequent start-and-stop cycles when operating at low load conditions, which disrupts the system oil return.

Innovation Solution

A low load operating system is introduced, featuring a hot gas bypass line from the compressor's discharge side to its suction side and a desuperheat line from upstream of the expansion valve to the suction side, along with an oil return line, monitored and controlled by a controller to manage compressor operation during low load conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the compressor rack is unloaded to match low load conditions, then the system adapts to low load operation, but the compressors stop and start frequently causing damage and disrupting oil return

Engineering Contradiction:

Improveload matching capabilityVSAvoidcompressor operation stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

A hot gas bypass line is introduced as an intermediary pathway that allows high-pressure discharge gas to bypass the evaporator and return to the suction side. This mediator enables the compressor to maintain continuous operation at low load by recirculating gas, preventing the frequent start-stop cycles that would otherwise occur when load demand is below compressor capacity

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system performs preliminary action by proactively opening the hot gas bypass valve before the compressor would otherwise shut down due to low load conditions. This anticipatory measure maintains suction pressure and prevents compressor cycling, ensuring continuous operation and stable oil return

Inventive Principle:

Principle #10Preliminary action

2Productivity

If the compressors stop and start frequently to match very low load conditions, then the system maintains minimum capacity output, but this causes damage to the compressors and disrupts system oil return

Engineering Contradiction:

Improveminimum capacity outputVSAvoidcompressor damage and oil return disruption

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The hot gas bypass line serves as a mediator that allows the compressor to maintain continuous operation by recirculating discharge gas back to the suction side. This prevents the harmful effect of frequent start-stop cycles and ensures stable oil return to the compressor crankcase

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system converts what would be waste heat in the discharge gas into a beneficial resource by routing it through the hot gas bypass line to maintain suction pressure and prevent compressor cycling. The previously harmful frequent shutdowns are transformed into continuous stable operation

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 solution prevents frequent compressor starts and stops, ensures proper oil return, and extends the lifespan of refrigeration system components by maintaining stable operation during low load conditions.

Implementation Method 1

a vapor refrigerant is compressed within one or more compressors at high pressure and high temperature

Methodology Applied

Scientific EffectGas compression and pressure differential: Compression

Implementation Method 2

a hot gas bypass line extending from a discharge side of the compressor to a suction side of the compressor

Methodology Applied

Scientific EffectPressure gradient flow: Pressure Gradient

Implementation Method 3

the compressed vapor is cooled and condensed within a condenser by heat exchange with ambient air

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Implementation Method 4

the liquid refrigerant is passed through an expansion device that reduces both the pressure and the temperature

Methodology Applied

Scientific EffectPressure reduction: Depressurisation

Data Source

PatentUS10215465B2Systems and methods for low load compressor operations

Publication Date: 2019.02.26 HEATCRAFT REFRIGERATION WUXI CO LTD

AI summary

The present application provides a low load operating system for a refrigeration system having a compressor, a condenser, an expansion valve, and an evaporator. The low load operating system may include a hot gas bypass line extending from a discharge side of the compressor to a suction side of the compressor and a desuperheat line extending from upstream of the expansion valve to the suction side of the compressor.