Microchannel Condenser Start-Up Using Reheat Cycle Pressure Relief

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Solution Overview

Problem

Microchannel heat exchangers in refrigerant systems are susceptible to pressure spikes due to their low internal volume and sensitivity to refrigerant charge, leading to system shutdowns and compressor failure during start-ups, especially when high pressure spikes occur.

Innovation Solution

A reheat cycle is introduced with a refrigerant flow control device routing refrigerant through a reheat heat exchanger positioned on the high pressure side of the system, increasing the combined internal volume and reducing pressure spikes by actuating the reheat cycle at start-up and during conditions that may cause high pressure spikes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If microchannel heat exchangers are used as condensers, then heat exchange efficiency and compactness are improved, but the system becomes susceptible to pressure spikes and high pressure alarms during start-up

Engineering Contradiction:

Improveheat exchange efficiencyVSAvoidsystem stability during start-up

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The reheat cycle is activated before the main cooling cycle during system start-up. This preliminary action allows the refrigerant to circulate through the microchannel condenser gradually, preventing sudden pressure spikes that would trigger high pressure alarms and system shutdowns.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The reheat heat exchanger acts as an intermediary component that mediates between the compressor and the microchannel condenser during start-up. It provides an alternative pathway for refrigerant flow, reducing the thermal shock and pressure surge on the microchannel condenser.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Volume of moving object

If microchannel heat exchangers are used, then device compactness and structural rigidity are improved, but internal volume is reduced leading to higher sensitivity to refrigerant charge variations

Engineering Contradiction:

Improvedevice compactnessVSAvoidtolerance to refrigerant charge variations

Core Design Contradiction:

Volume of moving objectVSAdaptability or versatility

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes operational parameters by activating the reheat cycle, which modifies refrigerant flow distribution and pressure characteristics. This parameter change allows the system to operate safely with the reduced internal volume of microchannel heat exchangers.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the reheat cycle is activated during start-up, then pressure spikes are reduced and system reliability is improved, but device complexity increases

Engineering Contradiction:

Improvesystem operation continuityVSAvoidcycle configuration complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The reheat heat exchanger serves multiple functions: it acts as a heat exchanger during normal operation and as a pressure-regulating component during start-up. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in system complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The refrigerant flow control device dynamically switches between routing refrigerant through the reheat heat exchanger during start-up and through the normal cooling cycle during operation. This dynamic operation allows the system to adapt to different operational phases without requiring permanently active additional components.

Inventive Principle:

Principle #15Dynamics

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 nuisance shutdowns and maintains stable temperature and humidity control, reducing compressor failure risks and ensuring continuous operation by mitigating pressure spikes and allowing for efficient dehumidification and heating adjustments.

Implementation Method 1

The reheat heat exchanger is typically positioned in the path of the air downstream of the evaporator. With a reheat cycle actuated, air can be cooled in the evaporator below normally desirable temperature, allowing for a greater amount of moisture removal from the air stream. The air then passes over the reheat heat exchanger and is heated back toward the target temperature.

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 2

the refrigerant is evaporated and typically superheated, while cooling and often dehumidifying this secondary fluid

Methodology Applied

Scientific EffectCondensation: Condensation

Data Source

PatentEP2304340B1Start-up procedure for refrigerant systems having microchannel condenser and reheat cycle

Publication Date: 2018.09.12 CARRIER CORP

Figure 1A~3
Figure 2A~2B

AI summary

A refrigerant system has a condenser of microchannel design and construction and includes a reheat cycle. The reheat cycle includes a refrigerant flow control device, such as a three-way valve, for selectively routing at least a portion of refrigerant through a reheat heat exchanger from a location between a compressor and expansion device. A control for the refrigerant system selectively actuates this refrigerant flow control device to route at least a portion of refrigerant through the reheat heat exchanger at system start-up.