Achieving Airflow and Static Pressure Regulation in Fabric Duct Systems

       Fabric ducts are made of special polymer fiber materials. Internally pressurized by fans, they release air uniformly through micro-perforations or custom openings in the fabric. Unlike traditional metal ducts that rely on discrete outlets, the fabric duct itself serves as the air terminal, with the entire surface acting as an outlet. This enables comfortable, large-area, low-velocity, draft-free air distribution.

During operation, the system maintains a specific internal static pressure to ensure stable airflow release from the duct surface. The balance of airflow distribution and static pressure depends on the synergy of fabric permeability, opening patterns, duct geometry, and auxiliary regulation devices.

       The core of fabric duct systems lies in their "permeable" nature. Manufacturers offer fabrics with different permeability classes (e.g., Class 0 to Class 5) based on ventilation requirements. Low-permeability materials (e.g., Class 0) are nearly airtight and require sewn or laser-cut openings, while high-permeability materials (e.g., Class 3–5) allow air to seep naturally through micro-perforations. Selecting the appropriate permeability class allows for pre-setting the overall airflow distribution during the design phase.

       For areas requiring precise local airflow control, the system can use laser cutting or thermal forming to create circular, slit-shaped, or custom-shaped openings at specific locations. The size, density, and arrangement of these openings are optimized via CFD (Computational Fluid Dynamics) simulations to ensure on-demand airflow distribution along the duct length. For example, in large workshops, openings near the fan can be smaller, while those farther away are larger, compensating for pressure losses along the duct and achieving uniform airflow.

        Although fabric ducts possess excellent self-balancing characteristics, mechanical regulation is still necessary in complex scenarios (e.g., multi-branch systems or spaces with frequent load changes). Modern fabric duct systems often integrate adjustable dampers, zippered airflow regulators, or internal damping curtains. Operators can use external handles or electric actuators to adjust local resistance in real time, changing the airflow from that duct section and achieving dynamic airflow balancing.

       A major advantage of fabric ducts is their "self-balancing static pressure" capability. When the total airflow is constant, if a section of outlets is partially blocked or environmental resistance changes, the static pressure in that area automatically increases, forcing more air to flow out from unobstructed areas. This maintains overall airflow uniformity. This passive regulation requires no additional control equipment, significantly enhancing system robustness.

       When inflated, fabric ducts expand slightly, with their cross-section tending toward a circular shape and the inner wall becoming smooth, effectively reducing airflow friction resistance. More importantly, this flexible structure can deform slightly with changes in internal static pressure: when static pressure increases, the duct diameter slightly increases, expanding the flow area and helping to suppress pressure spikes; the opposite occurs when pressure decreases. This physical feedback mechanism acts as a "buffer," stabilizing the system's static pressure.

       At the connection between the fan outlet and the main duct, a plenum chamber or stabilization section is typically installed. This structure eliminates fan pulsations, equalizes airflow, and provides a stable inlet static pressure for the fabric duct. Especially in VAV (Variable Air Volume) systems, the plenum chamber, used in conjunction with variable-frequency fans, can dynamically adjust the total airflow based on terminal demand while maintaining the minimum required static pressure for the fabric duct (typically 50–150 Pa), preventing airflow unevenness or duct collapse due to insufficient pressure.

        With the development of building automation, high-end fabric duct systems are beginning to integrate sensors and intelligent control modules. By placing static pressure sensors and airflow probes at key nodes, the system can monitor operating conditions in real time and feed data back to a central controller. Combined with variable-frequency fans and electric control valves, this enables closed-loop control based on actual loads: when temperature or CO₂ concentration changes in a specific area, the airflow to that zone is automatically adjusted while coordinating global static pressure balance.

       Furthermore, the application of BIM (Building Information Modeling) technology makes duct design more precise. Engineers can simulate different permeability classes, opening schemes, and static pressure distributions in a virtual environment, optimizing system performance in advance and reducing on-site commissioning costs.