An Analysis of the Working Principles of Fiber Fabric Ducts

       As modern buildings place increasing demands on indoor air quality, energy efficiency, and comfort, traditional metal duct systems are gradually revealing limitations in certain application scenarios. Against this backdrop, fiber fabric ducts (also known as textile ducts, fabric air dispersion systems, or fabric ductwork), as a new type of ventilation terminal device, have been widely adopted in fields such as food processing, pharmaceutical cleanrooms, sports venues, commercial spaces, and industrial plants due to their advantages of being lightweight, aesthetically pleasing, easy to install, and providing uniform air distribution. This article systematically elaborates on the working principles of fiber fabric ducts, deeply analyzing their operating mechanisms from aspects such as structural composition, airflow organization methods, permeation and jet mechanisms, and temperature and humidity control characteristics, while briefly comparing their differences with traditional metal ducts.
1. Basic Composition of Fiber Fabric Ducts
       Fiber fabric ducts are typically made of polymer fibers (such as polyester, polypropylene, etc.) through special weaving processes, possessing certain air permeability, strength, and flame-retardant properties. According to air supply requirements, the fabric materials can be categorized into fully permeable, micro-permeable, non-permeable, and hybrid types. Insulation layers are generally not installed inside the ducts; instead, thermal insulation is achieved through the low thermal conductivity of the fabric itself and the air layer. Some high-end products also feature internal coatings with antibacterial, anti-mold, or anti-static properties to meet the requirements of specific environments (such as cleanrooms and cold storage).
       The ducts are suspended below ceilings or roof trusses via hanging methods and connect to the main ducts of central air conditioning systems. Their cross-sections are mostly circular or semi-circular, with diameters determined based on airflow volume and velocity calculations. Unlike traditional metal ducts, fiber fabric ducts serve as the air supply terminal themselves and do not require the additional installation of diffusers or vents.
2. Core Working Principle: Combination of Permeation and Directional Jet
       The core working principle of fiber fabric ducts lies in utilizing the controllable permeability of the fabric material and preset air supply holes/slits to achieve two main airflow organization methods: overall permeation air supply and directional jet air supply. These two methods can be used individually or combined according to engineering requirements, thereby achieving more precise and uniform air distribution.
(1) Permeation Air Supply Mechanism
       For ducts using microporous or fully permeable fabrics, when the fan delivers treated air into the duct, due to the static pressure inside the duct being higher than the external environment, the air slowly and uniformly "seeps out" into the surrounding space through the tiny pores between the fabric fibers. This air supply method has the following characteristics:
Draft-free and Low Noise: Air diffuses at an extremely low speed (usually less than 0.2 m/s), avoiding the localized draft sensation caused by traditional vents and enhancing human comfort.
Large-area Uniform Air Supply: The entire surface of the duct can serve as the air supply surface, effectively eliminating dead zones, making it particularly suitable for high-ceiling spaces (such as gymnasiums and warehouses).
Condensation Suppression: In low-temperature air supply scenarios (such as cold storage), permeation air supply can make the duct wall temperature approach the supply air temperature, reducing the temperature difference between the inside and outside, thus effectively preventing condensation.
Permeability is a key parameter measuring the fabric's air supply capacity, with units of L/(m²·s) or CFM/ft². During design, the fabric type must be precisely selected based on the required air volume, duct length, and static pressure loss.
(2) Directional Jet Air Supply Mechanism
       In scenarios requiring long-distance air supply or guidance of airflow in specific directions, fiber fabric ducts open circular holes, strip slits, or install specialized nozzles at specific locations. These openings are optimized through fluid dynamics design to form air jets with a certain initial velocity and range, achieving directional air supply. Its working principle is similar to that of traditional diffusers but offers greater flexibility:
Customizable Air Supply Angle and Distance: By adjusting the size, number, and arrangement of the holes, the coverage range and landing points of the jets can be controlled.
Induction of Surrounding Air Mixing: High-speed jets entrain surrounding air during movement, enhancing air mixing efficiency and helping to quickly eliminate indoor temperature differences.
Suitable for Stratified Air Conditioning: In high-ceiling spaces, upper jets can achieve an "upper supply, lower return" stratified air conditioning strategy, saving energy.
It is worth noting that jet air supply usually coexists with permeation air supply. For example, the main body of the duct uses micro-permeable material to maintain basic uniform air supply, while additional jet holes are added above densely populated areas or heat sources to enhance local ventilation.
3. Static Pressure Distribution and Airflow Stability
        The static pressure distribution inside the fiber fabric duct is crucial to its air supply uniformity. Ideally, the entire duct should maintain a relatively constant static pressure to ensure consistent permeation at all locations. However, due to pressure losses caused by frictional resistance along the path and local air supply, the actual static pressure gradually decreases along the airflow direction.
To solve this problem, modern fiber fabric ducts often adopt "variable diameter design" or "zoned air supply" strategies:
Variable Diameter Design: The duct diameter gradually decreases along the airflow direction to compensate for the static pressure drop, maintaining a constant air supply volume per unit area.
Multi-segment Independent Air Supply: Long-distance ducts are divided into several sections, with each section supplied by an independent branch duct to avoid insufficient air supply at the terminal.
Furthermore, the flexibility of the fabric material allows it to slightly expand or contract with changes in internal pressure. This "self-adaptive" characteristic also helps buffer transient pressure fluctuations, improving system stability.
4. Temperature, Humidity, and Cleanliness Control Characteristics
        Fiber fabric ducts exhibit unique advantages in temperature and humidity control. Due to their large air supply area and low wind speed, cold/hot air can blend into the indoor environment more gently, reducing vertical temperature differences (such as the "hot head, cold feet" phenomenon). In low-temperature air supply systems, permeation air supply can make the duct wall temperature approach the supply air temperature, significantly reducing the risk of surface condensation—a problem difficult for traditional metal ducts to overcome.
        In cleanroom applications, some high-end fabric ducts use antibacterial fibers or internal filter linings to effectively inhibit microbial growth. Meanwhile, their smooth inner surface does not easily accumulate dust and can be disassembled and cleaned as a whole, making maintenance convenient and meeting hygiene standards such as GMP and HACCP.