Multi-Stage Compressor Pressure Control for Four-Way Valve Protection

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Solution Overview

Problem

The large pressure difference in multi-stage compression refrigeration cycles leads to increased load on the four-way switching valve, potentially causing damage and pipe damage due to the switching impact.

Innovation Solution

A controller is used to manage the operation of the compressors and four-way switching valve by stopping the low-stage compressor and reducing the rotational speed of the high-stage compressor, and utilizing a bypass pipe with a control valve to equalize pressures, thereby reducing the load on the four-way switching valve.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a four-way switching valve is used in a multi-stage compression refrigeration cycle, then the refrigeration cycle can be operated, but the large pressure difference increases the load on the valve causing potential damage

Engineering Contradiction:

Improvereliability of heat source unitVSAvoidload on four-way switching valve

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

The controller stops the low-stage compressor before actuating the four-way switching valve, and reduces the rotational speed of the high-stage compressor to minimize the pressure difference. This preliminary action of adjusting compressor operations before valve switching reduces the load on the valve and prevents damage while maintaining system reliability

Inventive Principle:

Principle #10Preliminary action

2Productivity

If the four-way switching valve is switched under large pressure difference, then the refrigeration cycle operation is maintained, but the impact generated may damage the pipe connected to the valve

Engineering Contradiction:

Improverefrigeration cycle operationVSAvoidimpact damage to pipe

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The controller performs preliminary actions by stopping the low-stage compressor and reducing the high-stage compressor rotational speed before switching the four-way switching valve. This minimizes the pressure difference and consequently reduces the impact force on the connected pipe during valve switching, preventing pipe damage while maintaining refrigeration cycle operation

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

By adjusting the operational state of compressors before valve switching, the system creates a cushioning effect that reduces the pressure difference and impact force on the pipe during the critical valve switching moment, thereby protecting the pipe from damage

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentEP4303504B1Heat source unit and refrigeration apparatus

Publication Date: 2025.07.02 DAIKIN INDUSTRIES LTD

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AI summary

A heat source unit (10) connected to a utilization-side unit (50) and configured to perform a refrigeration cycle includes a low-stage compressor (23), a high-stage compressor (21), a four-way switching valve (150), a low-stage pipe (24c), and a controller (101). The low-stage pipe (24c) is provided in parallel with the low-stage compressor (23), and the refrigerant flows therethrough while the low-stage compressor (23) is stopped. The controller (101) outputs an instruction signal for actuating the four-way switching valve (150), to the four-way switching valve (150) while the low-stage compressor (23) is stopped and the high-stage compressor (21) is operating.