In HVAC systems, the thermal conductivity of ducts directly affects heat and cold loss, system energy efficiency, and operational stability. As a composite duct type integrating structure, insulation, and sound absorption, the thermal conductivity of fiberglass ducts has always been a key consideration in engineering selection. This article will systematically analyze the thermal conductivity of fiberglass ducts from the perspectives of material structure, heat transfer mechanism, and engineering performance.

I. Material Composition and Thermal Conductivity Basis of Fiberglass Ducts

Fiberglass ducts typically consist of the following parts:

Inner layer: High-density fiberglass insulation layer

Middle layer: Reinforced fiberglass structural layer

Outer layer: Moisture-proof and corrosion-resistant cladding material (aluminum foil, composite film, etc.)

Fiberglass itself is an inorganic fiber insulation material, composed of numerous fine fibers and still air. This structure lays the foundation for its relatively low thermal conductivity.

II. Mechanism of Thermal Conductivity in Fiberglass Ducts

1. Fiber Structure Extends Heat Transfer Path

The glass fibers are irregularly interwoven:

Heat constantly refracts between the fibers

The solid heat transfer path is significantly lengthened

The actual heat flux density is reduced

This "tortuous heat transfer path" is one of the core reasons for the stable thermal conductivity of fiberglass ducts.

2. Still Air Reduces Gas Thermal Conductivity

Fiberglass ducts contain a large amount of enclosed or semi-enclosed air:

Air has a low thermal conductivity

Air is confined by the fibers, making convection difficult

The contribution of gas thermal conductivity is effectively controlled

This makes convective heat transfer in fiberglass ducts almost negligible under normal operating conditions.

3. Synergistic Effect of Composite Coating Materials

The outer aluminum foil or composite film coating provides:

Blocks water vapor penetration

Reduces radiative heat exchange

Improves overall thermal resistance stability

While the coating material does not directly determine the thermal conductivity, it is crucial for the long-term stability of thermal conductivity.

III. Engineering Understanding of Fiberglass Duct Thermal Conductivity

In engineering applications, the thermal conductivity of fiberglass ducts is typically reflected in the following aspects:

Overall thermal conductivity is significantly lower than that of metal ducts.

Effectively reduces heat loss during air supply.

Stable performance in medium and low temperature air conditioning systems.

It should be noted that the thermal conductivity of fiberglass ducts is a comprehensive structural performance characteristic, not a single material parameter, and cannot be simply equated to a single numerical value for comparison.

IV. Key Factors Affecting the Thermal Conductivity of Fiberglass Ducts

1. Fiberglass Density

Too low density: Increased risk of air convection.

Too high density: Increased proportion of solid-to-solid heat transfer.

A reasonable density range helps to balance thermal conductivity.

2. Duct Thickness Design

The greater the thickness, the higher the overall thermal resistance.

Thickness should be determined comprehensively based on the system temperature difference and operating environment.

Thicker is not necessarily better; it should meet the design conditions.

3. Construction and Sealing Quality

Improper joint treatment can create thermal bridges.

Damaged lining can affect moisture-proofing and insulation performance.

Proper installation is a crucial prerequisite for ensuring optimal thermal conductivity.

V. The Practical Significance of Fiberglass Duct Thermal Conductivity in HVAC Systems

From a system perspective, good thermal conductivity can bring the following benefits:

Reduced energy loss during heat and cold transfer

Improved air conditioning system operating efficiency

Reduced condensation risk

Extended equipment and pipe lifespan

This is one of the reasons why fiberglass ducts are widely used in public buildings, commercial spaces, and industrial plants.

VI. Comparison of Thermal Conductivity between Fiberglass Ducts and Traditional Metal Ducts

Under the same operating conditions:

Metal ducts require an additional insulation layer.

Fiberglass ducts already possess insulation properties.

After comprehensive construction, fiberglass ducts more easily achieve a continuous and stable insulation system. Therefore, from the perspective of system integrity, fiberglass ducts have a significant advantage in thermal conductivity control.

The thermal conductivity of fiberglass ducts stems from their fiberglass-air composite structure and integrated design. By extending the heat transfer path, suppressing air convection, and employing a well-designed surface covering, fiberglass ducts effectively control heat and cold loss in HVAC systems, providing stable support for energy-efficient system operation.