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Application of air-conditioning duct and thermal insulation material
In the ventilation project, the air duct should be made of suitable material according to the project requirements. Design and construction personnel need to fully understand the air ducts of different material properties and their use, application occasions, and under what circumstances the air ducts need to be insulated, so as to build a reasonable and durable ventilation pipe network system.
The materials used in ventilation ducts are commonly used in the following categories:
A: Sheet metal, sheet metal is the main material for making air ducts and components.
(1) Ordinary thin steel plate has good processing performance and structural strength, and is often used in general ventilation ducts and dust removal ducts. The surface is easy to rust and should be painted for anti-corrosion.
(2) Galvanized steel sheet is made of ordinary thin steel sheet galvanized, and its surface is protected by a zinc layer to prevent rust. Because of its silver-white surface, it is also called "white iron sheet". White iron sheet is generally thin in thickness, and is often used in air-conditioning systems without dust and wear in the gas and in humid environments that are not affected by acid mist.
(3) Aluminum and aluminum alloy plates have good processing performance, corrosion resistance, and are not easy to generate sparks during friction, but the cost is high, and they are often used in ventilation systems that require explosion-proof.
(4) Stainless steel plate has good corrosion resistance, and its cost is high, but it is only required for high corrosion resistance, such as ventilation pipes of chemical systems.
B: Non-metallic materials. There are many types of non-metallic materials used in ventilation pipes, but their applications are not as common as metal sheets.
(1) Hard polyvinyl chloride, strong acid, alkali and corrosion resistance, good machinability, smooth surface and convenient construction. Often used in ventilation systems with corrosive gases. However, rigid PVC is not resistant to high temperature, the operating temperature is generally not more than 60 degrees, and the linear expansion coefficient is large, so it is not easy to age and fire.
(2) FRP, which is a composite material made of glass fiber products as reinforcing materials and resins as binders through a certain molding process. Good corrosion resistance, commonly used in exhaust systems containing corrosive gases and water vapor
(3) Plastic composite steel plate, which is to spray a layer of 0.2-0.4mm thick plastic layer on the surface of ordinary thin steel plate. This kind of steel plate is more expensive, 50% more expensive than ordinary carbon steel plate.
(4) Bricks and concrete, which are the most common building materials, are often used to utilize building space or lay underground air ducts.
Usually, the ducts of the above materials are used in the following applications:
1) Thin steel plate: general ventilation and air conditioning system: 0.5~1.5mm; dust removal system: 1.5~3.0mm.
2) Plastic plate: Ventilation system containing corrosive gas.
3) Inorganic FRP: occasions with high humidity.
4) All kinds of hoses: metal, plastic, and some with insulation layer.
5) Composite air duct: double-layer aluminum foil plus phenolic resin, single-layer aluminum foil plus glass fiber, commonly used in air-conditioning systems with high dust-proof requirements and corrosion-resistant systems at -10℃~70℃.
6) New flexible air duct: uniform and superior air distribution, avoiding the feeling of blowing; light weight, convenient and fast installation, low structural requirements; good flexibility, easy to change the system; easy to clean.
In the following cases, our construction personnel should insulate the air duct:
(1) Due to the excessive cold and heat loss, the lack of heat preservation is economically unreasonable;
(2) Due to the loss of cold and heat, the temperature of the medium cannot reach the temperature required by the design;
(3) Due to heat loss, the temperature of the gas transported in the air duct is reduced to the point where it is possible to condense or freeze in the air duct or in the subsequent dry dust collector;
(4) Condensation occurs on the outer surface of the air duct due to the loss of cooling capacity;
(5) Due to the transport of high-temperature gas, the temperature of the outer surface of the air duct is too high (for example, greater than 50 °C), which may cause burns to operators and maintenance personnel, or cause gas, steam, and dust explosions and fires.
The specific requirements for insulation materials are:
(1) The thermal conductivity is small, generally not exceeding 0.23W/m•K;
(2) The material has high porosity and low density, and the density generally does not exceed 600kg/m3;
(3) It has a certain compressive strength and is not easy to deform;
(4) Low hygroscopicity and no corrosive effect on the pipe wall;
(5) It is not suitable to use organic substances and flammable substances, otherwise anti-corrosion and fire-proof treatment should be carried out.
(6) When used in high temperature pipelines, it should be resistant to high temperature and have stable performance at high temperatures;
(7) It is easy to construct and install, and the cost is low.
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