What Is the Ventilation Duct?

Ventilation ducts are essential components in ventilation and air conditioning systems, serving as the common pipelines that transport air. They vary in material and design, each offering unique characteristics. This article explores different types of ventilation ducts, their advantages and drawbacks, and provides guidance on selecting appropriate air duct fabrication machines to meet project needs.

Iron Sheet Air Duct

Advantages of Iron Sheet Air Duct

Iron sheet air ducts, typically made from galvanized steel, offer high strength and can withstand wind pressures up to 3000 Pa, making them suitable for high-, medium-, and low-pressure air systems. They can be processed directly on-site, which reduces transportation costs, allows for easy adjustments, and ensures minimal impact on the construction timeline.

Defects of Iron Sheet Air Duct

Despite their strengths, iron sheet air ducts have several limitations. They are prone to rusting, resulting in a shorter service life that negatively affects indoor air quality; in humid environments, they may last only 5-7 years, with rust accumulating inside after 4-5 years. Their air leakage rate is high, around 10% (as permitted by national standards), leading to increased energy consumption. The thin walls generate noticeable noise under wind speed and pressure. They are also heavy, exceeding 10 kg per square meter, which adds significant load to the building structure. High thermal conductivity requires external insulation, raising project costs and extending timelines; improper or damaged insulation can create cold bridges, causing condensation that damages ceilings and nearby items. Production and installation cycles are lengthy due to the need for large-scale machinery, undercutting, and flanging. Maintenance is costly, as regular rust prevention is required. The appearance is often unappealing, especially after external insulation, and they occupy substantial ceiling space (typically 40-60 mm) when including flanges and insulation thickness.

Aluminum Foil Composite Glass Fiber Duct

Aluminum foil composite glass fiber ducts are produced directly from superfine glass wool, the insulation material commonly used with iron sheet ducts. Introduced to the domestic market in 1992 as super air ducts (glass fiber ducts), they have been available for over three decades but maintain a relatively small and even shrinking market share.

Advantages of Aluminum Foil Composite Glass Fiber Duct

These ducts provide excellent sound absorption due to the loose structure of the superfine glass wool. They are also lightweight, weighing approximately 3 kg per square meter.

Defects of Aluminum Foil Composite Glass Fiber Duct

The material has poor strength and low pressure-bearing capacity, limiting use to low-pressure, small ducts. It requires careful finished product protection, as it is easily damaged during subsequent hydropower or decoration work, and cannot be cleaned effectively. It is highly susceptible to moisture, with ultrafine glass wool absorbing significant water if the surface sealing is inadequate, particularly after slotting, which reduces insulation performance and strength. Fibers can disperse if sealing is poor, posing health risks. The surface roughness (0.9-1.1 mm) creates large wind resistance, often requiring a 10% increase in unit power and raising energy consumption.

Aluminum Foil Polyurethane Duct

Aluminum foil polyurethane ducts feature polyurethane in the middle with composite aluminum foil on both sides. They are notably lightweight, but their primary shortcoming is poor fire performance that fails to meet national standards. Regulations for high-rise and civil buildings require non-combustible materials for ventilation ducts, yet these reach only B1 level at best, including accessories and glue. They also suffer from low strength and limited pressure-bearing capacity.

Aluminum Foil Composite Phenolic Duct

Phenolic ducts use phenolic as the insulation material with composite aluminum foil on both sides. They offer the advantage of being lightweight, but exhibit significant drawbacks, including poor strength, easy pulverization, delamination between aluminum foil and phenolic, use of strong acids in foaming, and organic glue containing formaldehyde, making them less environmentally friendly.

Color Steel Plate Air Duct

Color steel plate air ducts come in single-sided and double-sided varieties. Single-sided versions relocate the superfine glass wool from the outside to the inside, with color steel on the exterior and glass wool inside. Double-sided versions add an iron sheet protection layer outside the insulation cotton of traditional iron sheet ducts. These represent limited technological advancement over iron sheet ducts, essentially modified versions. Key improvements include using PVC inserts instead of biting and flanging, along with one-time forming of insulation cotton and color steel plate without secondary insulation.

Advantages of Double-Sided Color Steel Plate Air Duct

Airtightness improves due to PVC inserts replacing biting and flanging, reducing the air leakage rate. No secondary insulation is needed, enhancing construction efficiency. The service life is extended compared to basic iron sheet ducts.

Defects of Double-Sided Color Steel Plate Air Duct

Replacing biting and flanging with PVC inserts compromises the duct's integrity, reducing fire resistance (PVC reaches only B1 level) and eliminating the iron sheet's toughness advantage. Better sealing could be achieved through improved construction quality or plugging in traditional iron sheet ducts. Internal glass wool can disperse after slotting, with sealing challenges affecting health. Cleaning is difficult: glass wool interiors resist cleaning, while color steel interiors risk paint damage from brushes, shortening lifespan. Strength is significantly lower than iron sheet ducts, as color steel thickness is only 0.3 mm (versus 0.5 mm minimum for iron sheet), requiring reinforcement and closer support spacing, increasing costs. Factory-produced ducts limit on-site adjustments. PVC flanges lack the strength of metal biting and flanging, creating weak points.

Glass Magnesium Duct

Glass magnesium ducts stand out for their energy-saving and environmental benefits, reducing system operating costs by more than 10% compared to iron sheet ducts. Performance is evaluated by resistance, air leakage rate, and insulation; glass magnesium excels in these areas with low resistance, minimal leakage, and superior insulation.

It delivers clean air and improves indoor air quality (IAQ) by avoiding rust, mildew, dust, bacteria, fungi, odors, and fiber dispersion. Sound insulation averages 21 dB, with insulation material providing vibration reduction and sound absorption to minimize noise from air vibration, machinery, and duct expansion/contraction.

High-quality glass magnesium ducts feature excellent fire performance (Class A non-combustible, per national standards), high strength (bearing over 1000 N and 3000 Pa wind pressure for all pressure systems), superior moisture-proofing (maintaining 80% wet strength even when immersed), space-saving design via flange-free connections, lighter weight (7 kg per square meter, 30% less than iron sheet), attractive appearance allowing secondary painting, no cold bridges for better energy efficiency, and efficient on-site assembly without heavy machinery.

Other Commonly Used Ventilation Ducts in HVAC Systems

In addition to the above, several other types are prevalent in HVAC engineering.

Galvanized iron sheet air ducts remain a traditional option, suitable for low-moisture gas transmission but limited by rusting, poor corrosion resistance, lack of noise reduction and insulation (requiring added mufflers and layers), long production cycles, inconvenient installation, persistent noise, and short lifespan.

FRP (glass fiber reinforced plastic) air ducts, made from magnesium oxychloride reinforced with glass fiber, offer fire and corrosion resistance but are heavy, lack noise elimination and insulation (needing added layers), and resist on-site modifications post-design.

Composite fiberglass ducts (also known as new super ducts) use centrifugal fiberglass boards with anti-moisture aluminum foil outside, glass fiber cloth inside, and glue spraying. They are lightweight, compact, easy to install, space-efficient, modifiable, fire- and moisture-resistant, noise-reducing, insulating, low-leakage, durable, and cost-effective, providing strong advantages for modern applications.

Application Performance of Ventilation Ducts

Composite fiberglass ducts demonstrate superior thermal insulation with low thermal conductivity and high heat reflection from outer aluminum foil, using tenon/T-shaped joints for uniform insulation without cold bridges (unlike galvanized iron or inorganic FRP ducts requiring added layers).

Fire performance is excellent (Class A non-combustible per standards), using flame-retardant adhesive and non-combustible base (compared to variable insulation in others).

Noise elimination is strong (18-21 dB/m for medium/high frequencies), acting as a natural muffler (unlike others needing added mufflers).

Moisture resistance is high with zero-permeability outer foil and low water absorption (≤2%), maintaining properties in humid conditions (unlike galvanized iron's corrosion or FRP's instability).

Air leakage is minimal (near 0% for non-reinforced, ≤2% system-wide), far below standards.

Weight is very low (2.8 kg/m² including hangers), the lightest among options.

Friction resistance is slightly higher but negligible in overall system impact.

Fiber shielding prevents dispersion, meeting health standards.

Application Effect and Prospect of Ventilation Ducts

Galvanized iron sheet ducts suit low-requirement environments for dry gases but may be phased out due to noise, short insulation life, and other issues.

FRP ducts offer fire/corrosion resistance for outdoor/corrosive settings but face declining use due to moisture issues, unstable quality, and unreasonable pricing.

Composite fiberglass ducts, a recent innovation, are gaining market share with superior overall performance, scientific design, ease of use, noise/insulation benefits, space savings, long life, and cost-effectiveness. They promise widespread adoption as technology advances.

In summary, composite fiberglass ducts excel in noise elimination, insulation, fire safety, moisture resistance, low leakage, stability, and value, adapting to various requirements while offering lightweight handling, easy modification, efficient construction, fewer seals, high thermal efficiency, quiet operation, and low comprehensive costs. Advancing new materials and technologies will better meet market demands.