Installation, starting and adjustment of ventilation and air conditioning systems A Guide
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Cylindrical fabric ducts are the most common. They are convenient if you need to provide intensive air exchange, preventing drafts. Semicircular air ducts are used in rooms with low ceilings, for example, in catering establishments, non-food stores, hotels, etc. Air ducts in a quarter-section of a circle can also be used, installed around the perimeter of the room.
Installation of steel ducts in rooms with high ceilings is quite laborious and time-consuming. The use of textile air ducts greatly facilitates the work. Sections of air ducts (usually 5 m long) are connected to each other with the help of zippers. The air ducts are suspended using stretched cables or rails. In the latter case, the fastening is more rigid, and the duct retains its shape even without air supply. When condensation occurs, a nutrient medium is formed that promotes the development of microorganisms. Textile ducts can be easily dismantled, washed or cleaned. They are produced with a diameter of 100 to 1000 mm and a length of up to 100 m, as well as various densities that allow changing the air supply from 160 to 500 m3 / g * m2 at a static pressure inside 100 Pa.
When transporting hot gases with a temperature of more than 100
In ventilation systems of residential, public and administrative buildings, as well as office and auxiliary premises of industrial enterprises, air ducts made of slag-alabaster, cinder-concrete, reinforced cement and plastic plates, bricks, concrete, etc
. are used for portable ventilation installations rubberized, as well as metal flexible hoses.
When laying rectangular vertical air ducts, they try to make the most of the internal walls, in which appropriate channels are left for this purpose. If this is not possible, side channels and shafts are mounted to the walls.
In addition, spiral-wound metal air ducts are used in construction practice, as well as plastic air ducts that resist corrosion (made of vinyl, polyisobutylene, etc.). Their disadvantage lies in the fact that they can only be used at a temperature of transported air no higher than 70 °C.
In addition to these modifications, the ducts can be flexible, semi-flexible, thermally insulated, and also acting as a muffler.
4.2. Metal air ducts
Most often, metal ducts are used in air conditioning systems, which have great strength and resistance to fire.
They are made of galvanized or stainless steel.
Spiral-lock round (with a folding connection). They are made of steel tape with an anti-corrosion coating 0.5–1 mm thick, about 130 mm wide. They have increased rigidity compared to straight-seam ducts, there is no length restriction, aesthetic appearance, high seam density. The disadvantages include the fact that the seam takes about 15% of the metal from which the duct is made.
Spiral-welded round. They are made of steel tape with an anti-corrosion coating 0.8–2.2 mm thick, about 400–750 mm wide. The joints are welded overlap. Spiral-wound air ducts have less metal consumption compared to spiral-lock air ducts, there is no length restriction, high seam density. However, they cannot be made from steel thinner than 0.8 mm.
Rectangular straight-folding air ducts. They are made of steel sheet, it is desirable to place the seam on the bend so that it serves as an additional stiffener. Such ducts are easier than round ones to place in a space with a limited height, they fit better into the interior of the building. Rectangular ducts have greater aerodynamic drag than circular ducts with similar performance.
Round straight-folding air ducts. According to the manufacturing method and material, they are similar to rectangular air ducts, they differ only in a circular cross section.
4.3. Metal-plastic air ducts
Metal-plastic air ducts consist of two layers of metal, between which foam plastic is laid. Usually such a construction is used: foamed plastic 2 cm thick, located between layers of corrugated aluminum 80 microns thick. They have a small mass with high strength. They have a smooth surface, aesthetic appearance, do not require additional thermal insulation.
4.4.Non-metallic air ducts
Non-metallic air ducts are made of synthetic materials: polyethylene, fiberglass, etc.
Polyethylene air ducts: are usually used in supply ventilation systems. When the fan is turned on, the duct (in the form of a sleeve) is inflated with air.
Fiberglass ducts: usually used to connect the fan and air distributors. They are stretched on a metal frame.
Vinyl plastic air ducts: used when moving air containing acid vapors, etc., causing corrosion of steel. The thickness of the vinyl plastic is 3–9 mm, connected by welding.
Non-metallic air ducts are resistant to corrosion, they can be bent in any plane and at any angle.
4.5. Flexible air ducts
Flexible ducts of circular cross-section, lightweight, do not need special turns, as a result of which the duct has fewer connections, which simplifies installation. However, flexible ducts create a large aerodynamic drag, which may be excessive with an extended network, so they are often used as connecting pipes of small length. Flexible ducts are divided into:
• Flexible aluminum ducts without heat and noise insulation;
• Aluminum ducts with polymer coating without heat and noise insulation;
• Highly flexible polyvinyl chloride ducts;
• Highly flexible insulated air ducts consisting of two layers of polyvinyl chloride coated with polyamide fabric. A flexible steel wire spiral is located between the two layers.
• Semi-rigid aluminum ducts with thermal insulation;
• Flexible heat-insulated sound-absorbing air ducts. They consist of:
– Micro-perforated air duct made of high-strength metallized polymer;
– 25- 50 mm of thermal insulation layer with a density of 16 kg/m3;
– An outer coating made of aluminum seamlessly reinforced with fiber.
These ducts have excellent noise reduction performance in the low frequency range. To reduce the possible consequences of the use of mineral fibers on human health, the inner sleeve has minimal perforation, a special acoustic film is placed between the inner sleeve and the insulation layer. This reduces the probability of fiber entrainment at normal air flow speeds to almost a minimum.