Air duct classification and system composition

Classification and system composition of air ducts

Ⅰ. Classification of air ducts

1. Air ducts for ventilation and air-conditioning projects are classified by material: metal air ducts, non-metallic air ducts and composite material air ducts.

(1) Metal air ducts are generally made of galvanized steel plate, ordinary steel plate, aluminum plate, stainless steel plate and other materials:

(2) Non-metallic air ducts are made of non-metallic materials such as FRP and PVC:

(3) The composite air duct is made of non-combustible material cladding and thermal insulation material inner plate, mainly including polyurethane aluminum duct, rice aldehyde aluminum foil, glass fiber composite board air duct, etc.

2. Air ducts are divided into shapes: rectangular air ducts, circular air ducts and oval air ducts.

3. According to the working pressure of the air duct: The air duct is divided into four grades: micro pressure, low pressure, medium pressure and high pressure according to its working pressure.

Ⅱ. The composition of the air duct system

The air duct system is composed of fans, air ducts and accessories, various valves, static pressure, muffler devices, flexible connections, and return air outlets.

1. The fan is the power equipment that conveys the air volume. According to the working principle, it is divided into three types: centrifugal type, axial flow type and tubular type. According to the purpose, it is divided into general, fire and smoke exhaust, roof, induction, anti-corrosion, dust exhaust and explosion-proof type. The main parameters of the fan include: air volume, air pressure and power.

2. The main accessories of the air duct. Including: elbows, three-way, four-way, various types of reducing pipes, special-shaped pipes, guide vanes, three-way lever valves, etc. of air ducts.

3. Air system valve. Mainly include fire dampers, regulating valves, check valves, etc.

4. Static pressure muffler. Including: static pressure box, muffler, muffler duct, muffler elbow, etc.

5. Flexible connection. Connect the short pipe between the fan and the air duct, take vibration reduction measures for the connection between the fan and the air duct, and use flexible connections. Generally, materials such as canvas, silicon-titanium composite, thermal insulation reinforced aluminum foil, etc. are used, and the length should be 100 ~ 300mm.

6. The air outlet is divided into supply air outlet and return air outlet. Types include single-layer louver, double-layer louver, diffuser, orifice outlet, rotating outlet, spherical outlet, etc.

Technical requirements for ventilation and air-conditioning duct systems

Ⅰ.General requirements for the production of air duct systems

1. The production and installation of the air duct system should be carried out in accordance with the approved construction drawings, contract agreements or project negotiation records, relevant internal construction plans and standard specifications.

2. The plates, profiles and other main materials used to make the air ducts should meet the design requirements and the relevant regulations of the current national standards, and have corresponding factory inspection certificates. The selected finished air duct shall be provided with a product qualification certificate or an on-site re-inspection of strength and tightness shall be carried out.

For example, the cladding material of the composite air duct sheet must be non-combustible material, and the internal thermal insulation material of the air duct with thermal insulation properties should not be lower than the non-combustible B1 level. The connectors used in the production of air ducts are all non-combustible or flame-retardant B1 grade materials. The specifications of the plates used in the air ducts should meet the requirements. The fire resistance grade of the air duct of the smoke prevention and exhaust system should meet the design requirements. The main body of the air duct, the frame connection fixing material and the gasket material, the valve parts, the thermal insulation material, the flexible short pipe and the muffler must be made of non-combustible materials. If there is no design requirement for the thickness of the air duct plate of the exhaust system, it can be selected according to the thickness of the air duct plate of the high-pressure system.

3. The production of air ducts and accessories should use mechanical processing. Usually semi-mechanical manual production on site, simple air duct production line production, factory air duct automatic production line production.

4. The splicing of metal air duct plates adopts bite connection, riveting, welding connection and other methods, and the connection between air duct and air duct adopts flange connection, thin steel plate flange connection, etc. The bite seam of the splicing of the air duct plate should be staggered, and there should be no cross-shaped seam; the plate connection seam should be straight, flat, tight and firm, without exposing the insulation layer, and meet the strength requirements of the connection with the structure. The welding seam of the flange connection should be well fused and full, and the four corners of the rectangular flange should be provided with bolt holes. For flanges of the same specification processed in the same batch, the arrangement and spacing of the bolt holes should be uniform and interchangeable.

For example, generally, metal plates with a thickness of less than or equal to 1.2mm are connected by a bite. Electric welding, hydrogen arc welding and other methods are used for air ducts with a thickness greater than 1.5mm. The air duct and the flange are connected by riveting or welding. The distance between rectangular flange bolts and rivets for medium and low pressure systems is less than or equal to 150mm, and for high pressure systems is less than or equal to 100mm.