Air ducts for ventilation systems
Air ducts and shaped parts used in ventilation, air conditioning and air heating systems. Air ducts can be made of different materials - depending on the nature and properties of the air blend, it can be sheet galvanized or black steel, stainless steel, aluminum, various plastics. As ducts can also be used built-in channels from brick, concrete. The widest use was made of air ducts made of sheet galvanized steel. The shape of the air ducts and shaped parts to them can be round and rectangular. Round air ducts for metal consumption and labor costs with comparable aerodynamic characteristics are more cost effective than rectangular air ducts. But often in practice, based on a specific situation (design of a suspended ceiling, design of a room, etc.), it is more expedient to use air ducts of a rectangular section. For the convenience of calculating, manufacturing, installing ducts and other elements of air networks the size of air ducts and components of ventsystems (their connecting sizes) are unified. Accepted invasive ruler of the sizes of air ducts (diameter, height or width on an external dimension), mm:
100; 112; 125; 140; 160; 180; 200; 224; 250; 280; 315; 355; 400; 450; 500; 560; 630; 710; 800; 900; 1000; 1120; 1250; 1400; 1600; 1800; 2000; 2240; 2500
Round air ducts
The air ducts of a circular cross-section, in which the air is transported at a temperature below 80oС, must be made of steel sheet thickness, no more than:
- round ducts with a diameter less than 250 mm - 0,5mm;
- round air ducts in diameter from 250 to 450mm - 0,6mm;
- round air ducts in diameter from 500 to 800mm - 0,7mm;
- round air ducts in diameter from 900 to 1250mm - 1,0mm;
- round air ducts in diameter from 1250mm - 1,2mm.
The network of air ducts should be made up of unified fittings (straight sections, drafts, transitions, tees, trunks, crosspieces and stubs) of appropriate diameters.
Air circuits of circular cross-section are spiral-swirling, straight-line, flanged and flexible.
Recently, spiral air ducts have become increasingly widespread due to the low cost of manufacturing. Spiral airborne ducts made of galvanized steel tape of 0.55 and 0.7 mm thickness in a fully automated cycle are manufactured. Their length can be from 1 to 6 m. Spiral-inverting air ducts are interconnected with the help of internal or external nipples. In addition, they produce a wide range of shaped parts. These are central and one-way transitions, divides into 15o, 30o, 45o, 60o and 90o, straight and angular tees, crosses, trunks, stubs and umbrellas. When mounting the channels, the connecting sections of the shaped parts are inside the air ducts, while there is an automatic sealing of the joints.
Somewhat less, but still apply straight-line round air ducts. The straight-line air ducts of a circular section made of sheet galvanized steel in the thickness of 0,5 - 0,7 mm are made in such a way that at the installation of the end of one air duct enters the beginning of another. Due to the high cost of production, straight-line round air ducts are used in ventsystems of small length or with certain technological requirements.
In ventsystems with large diameters and wall thickness of air ducts, where they require their periodic disassembly, as well as in systems of aspiration, circular air ducts with flange connection are used. Flanges are made from an angle, bent at a certain diameter and welded at the junction and stuffed on the air line. The sealing of the joints between the air ducts is carried out with the help of rubber or felt pads installed between two adjacent flange bolts.
Now very popular at installation of not very long ventilation systems have got flexible ducts. Flexible ducts are made of aluminum-polymer sleeves, reinforced with steel wire or corrugated aluminum sheet. In channel air conditioning systems and inflatable ventilation systems, insulated (insulated) flexible air ducts are used, with an outer layer of syntepon heater. Applied on long (more than 4m) sections, flexible ducts are not worth due to significant aerodynamic resistance. But in combination with steel rigid air ducts, flexible ducts get quite wide application. The sizes of flexible ducts are also standardized:
100mm - 4"; 125mm - 5"; 150mm - 6"; 200mm - 8"; 250mm - 10"; 315mm - 12"; 355mm - 14"
Flexible air ducts of larger diameters are also offered by some manufacturers, but they are extremely rarely used.
It should be noted that for special systems of ventilation, systems of aspiration, for various technological processes also flexible aerosols from polymeric materials, reinforced with a steel wire are used. The diameters and the material from which such flexible ducts are made are presented in large assortment, but are used mainly in special manufactures.
Rectangular air ducts
Rectangular air ducts should have a ratio of sides to no more than 6.3.
Rectangular air ducts, on which air is transported under temperature of 80oC, must be made of steel sheet thickness, not more than:
- Rectangular air ducts with a larger side size are less 250 mm - 0,5 mm
- Rectangular air ducts with a larger side from 300 to 1000 mm - 0,7 mm;
- Rectangular air ducts with a larger side from 1250 to +2000 mm - 0,9 mm
Rectangular air ducts are interconnected with shaped products by means of pre-filled flanges on their ends or a rail connection. The rail connection due to the great complexity of its manufacturing is used less often. The flanges are currently made from special mounting bushings and corners of appropriate sizes. Sealing between flanges of air ducts is carried out with the help of a special seal, adhered to one of the adjacent flanges. Air pipelines of a rectangular cross section are convenient to use where, for various reasons, there is a limit on the height of the ceiling laying.