Rectangular air ducts are core components used for air conveyance in ventilation and air conditioning systems, with a rectangular cross-section, widely applied in central air conditioning, fire smoke exhaust, and industrial ventilation. Compared to circular air ducts, rectangular air ducts have unique advantages in space utilization, aesthetics, and connection convenience, but also present challenges such as higher resistance and lower strength. The following is a comprehensive analysis of rectangular air ducts from multiple dimensions to help users deeply understand their characteristics and applications.

 

The core advantage of rectangular air ducts lies in their efficient space adaptability. In ceiling spaces with limited building height, rectangular air ducts can be fabricated into flat shapes, easily integrating with building structures, avoiding conflicts with pipelines such as water pipes and cable trays, and maximizing space utilization. Additionally, the rectangular structure facilitates decorative concealment, seamlessly integrating with interior decoration styles to enhance aesthetics. Connection with equipment such as rectangular diffusers and louvered air outlets is also more direct, simplifying the installation process.

 

However, rectangular air ducts have certain limitations. Under the same cross-sectional area, their wetted perimeter is larger than that of circular air ducts, leading to increased friction area between air and duct walls, resulting in higher wind resistance and energy loss. In terms of strength, rectangular air ducts rely on angle steel flanges or internal supports for reinforcement to prevent suction collapse under negative pressure or bulging under positive pressure. In manufacturing processes, rectangular air ducts mostly rely on manual plate cutting, seaming, and flange connection, with higher sealing requirements and lower production efficiency compared to automatically produced spiral circular ducts.

 

Materials for rectangular air ducts should be selected based on the properties of the conveyed air (such as temperature, humidity, corrosiveness) and engineering requirements. Galvanized steel sheets are the most commonly used material, with the galvanized layer providing good rust resistance, suitable for most air conditioning supply, return air, and general exhaust systems. Stainless steel sheets are used in场合 involving corrosive gases, high-temperature flue gas, or high cleanliness requirements (such as laboratories, hospitals). Aluminum alloy sheets are used in explosion-proof systems or special anti-corrosion scenarios.

 

Composite air ducts (such as phenolic and magnesium oxide materials) have become the preferred choice for medium and low-pressure air conditioning systems due to their inherent thermal insulation, light weight, and easy installation. FRP (Fiberglass Reinforced Plastic) air ducts, with characteristics of light weight, high strength, corrosion resistance, and high temperature resistance (up to 200℃), are widely used in harsh environments such as chemical, power, and environmental protection industries. In addition, color steel plates, combining corrosion resistance and decoration, are suitable for exposed installation occasions.

 

The manufacturing of rectangular air ducts mainly adopts two methods: seaming connection and welding. Seaming connection is suitable for thin-plate small-sized air ducts, with common forms including common-plate flanges (air duct steel plates directly folded to form flanges, fixed by angle codes and spring clips) and angle steel flanges (angle steel flanges welded or riveted at both ends of air ducts, connected by bolts). The former has high production efficiency and material savings, while the latter has high strength and is suitable for high-pressure systems. Welding is mainly used for stainless steel or steel plate air ducts, meeting scenarios with high temperature, high humidity, or high sealing requirements.

 

The following parameters should be noted when designing rectangular air ducts:

- Dimension annotation: Expressed as width (W) × height (H) (unit: mm or m), e.g., 400mm×200mm.

- Wall thickness: Selected according to air duct size and working pressure (low pressure, medium pressure, high pressure) in accordance with specifications; larger sizes or higher pressures require greater wall thickness.

- Wind speed: The wind speed in main ducts is usually 6-10 m/s, and reduced to 3-5 m/s in branch ducts and before air outlets to control noise and resistance.

- Air leakage rate: High-pressure systems have stricter sealing requirements.

- Reinforcement: When the length of the long side exceeds the specification value (e.g., 630mm), reinforcement is required through angle steel frames, screw internal supports, or beading to prevent deformation and vibration.

 

Rectangular air ducts are widely used in civil buildings (office buildings, shopping malls, hospitals), public facilities (subway stations, airports), and industrial plants. Their core advantage of space saving makes them irreplaceable in the construction field. Selection requires comprehensive evaluation of system pressure, noise, space, and cost requirements: circular air ducts can be used for main pipelines to reduce resistance, and branch ducts can be switched to rectangular air ducts for convenient connection to air outlets. For corrosive, high-temperature, or high-pressure environments, FRP or stainless steel materials can be selected; for scenarios with high space and aesthetic requirements, composite air ducts or color steel plates are more suitable.

 

In conclusion, rectangular air ducts are the cornerstone of ventilation systems. Reasonable selection of materials, processes, and parameters can significantly improve system efficiency and reliability.