HVAC Compressor Pump-Down and Accumulator to Prevent Slugging Damage

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Solution Overview

Problem

Conventional truck cab/sleeper HVAC systems face issues with compressor damage due to liquid refrigerant migration and subsequent compression, known as 'slugging', especially when the compressor is at a low point within the system.

Innovation Solution

A solenoid valve is activated to stop refrigerant flow before shutting down the compressor, allowing remaining low-pressure vapor to be pumped to the condenser, and an accumulator is added to prevent liquid refrigerant from entering the compressor upon restart, ensuring only vapor is compressed.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the compressor is positioned at a low point in the HVAC system, then installation ease and drainage are improved, but liquid refrigerant migrates to the compressor causing slugging and damage

Engineering Contradiction:

Improveinstallation easeVSAvoidcompressor reliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

An accumulator is introduced as an intermediary component between the evaporator outlet and compressor inlet. This accumulator captures liquid refrigerant that migrates from the evaporator and prevents it from entering the compressor, thus resolving the slugging problem while allowing the compressor to remain at a low point for easy installation and drainage.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Use of energy by moving object

If the compressor shuts down immediately when cooling is sufficient, then energy consumption is reduced, but liquid refrigerant accumulates at the compressor inlet causing slugging

Engineering Contradiction:

Improveenergy consumptionVSAvoidcompressor reliability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The system performs a preliminary action by continuing to run the compressor for a predetermined time after the cooling setpoint is reached. This preliminary continuation of operation prevents liquid refrigerant from accumulating at the compressor inlet by maintaining vapor flow through the system, thus preventing slugging when the compressor eventually shuts down to save energy.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If the compressor runs continuously to prevent slugging, then compressor reliability is improved, but energy consumption increases

Engineering Contradiction:

Improvecompressor reliabilityVSAvoidenergy consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The system uses feedback from temperature sensors and pressure switches to control compressor operation. The compressor runs continuously only when conditions indicate a risk of slugging (such as high ambient temperature or rapid cycling conditions), and shuts down when conditions are favorable, thus maintaining reliability while minimizing unnecessary energy consumption.

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 prevents compressor damage by eliminating slugging and ensures efficient operation by ensuring only vapor refrigerant is compressed, reducing the incidence of compressor failure and maintaining system performance.

Implementation Method 1

a solenoid valve is activated to stop refrigerant flow before shutting down the compressor, allowing remaining low-pressure vapor to be pumped to the condenser

Methodology Applied

Scientific EffectRefrigerant phase change and pressure differential: Phase Change

Implementation Method 2

an accumulator is added to prevent liquid refrigerant from entering the compressor upon restart, ensuring only vapor is compressed

Methodology Applied

Scientific EffectRefrigerant phase separation: Phase Change

Implementation Method 3

a compressor compresses vapor refrigerant from a low pressure to a high pressure

Methodology Applied

Scientific EffectGas compression: Compression

Implementation Method 4

As the condenser rejects heat QH to the environment, the high pressure vapor at the inlet of the condenser condenses into a high pressure liquid refrigerant

Methodology Applied

Scientific EffectHeat rejection and condensation: Condensation

Implementation Method 5

the low pressure liquid refrigerant flows from the expansion valve to an evaporator, where heat QC is received from the environment. In response, low pressure liquid refrigerant evaporates into a low pressure vapor refrigerant

Methodology Applied

Scientific EffectHeat absorption and evaporation: Evaporation

Data Source

PatentEP3581413B1Systems and methods for reducing slugging in HVAC compressor of vehicle

Publication Date: 2023.11.29 PACCAR INC

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AI summary

Systems and methods for heating and cooling a vehicle cabin (120) and a sleeper (140) are disclosed herein. A method for heating and cooling the vehicle includes: running a compressor (172) of an air-conditioning system; and sensing the temperature inside the cab of the vehicle. The method further includes, closing a path of refrigerant to the compressor by a solenoid valve (178-1, 178-2) upstream of the cabin evaporator (186-1) and the sleeper evaporator (186-2), pumping-down refrigerant by the compressor, and deactivating the compressor when a lower set point of the temperature inside the cab is reached.