Common Ventilation Duct Classification and Performance Comparison!
1. The air duct we generally refer to is mainly about the ventilation duct for the central air-conditioning system. And it is an important part of the air-conditioning system. At present, there are mainly four kinds of common air ducts:
1) Galvanized sheet steel air duct; 2) Inorganic FRP air duct; 3) Composite fiberglass air duct; 4) Fiber fabric air duct.
2.The basic characteristics of the four air ducts.
Galvanized steel sheet air duct: one of the earliest used air ducts, made of Galvanized steel sheet, suitable for the transportation of general gas with low moisture content, easy to rust, no heat preservation and noise reduction functions, with long production and installation period.
Inorganic FRP air duct: a relatively new type of air duct, made of glass fiber reinforced inorganic materials, non-combustible in case of fire, corrosion-resistant, heavy, hard but brittle, easily deformed and cracked by its own weight, no heat preservation and noise reduction performance. The production and installation period is long.
Composite glass fiber board air duct: the latest type of air duct in recent years, with centrifugal glass fiber board as the base material, glass cloth inside, and moisture-proof aluminum foil outside (imported board is coated with heat-sensitive black acrylic polymer inside, and the outer layer is di fabric/aluminum foil/kraft paper), which are compounded and dried with a special fireproof adhesive, and then made by cutting, slotting, bonding and reinforcement procedures, and are connected and sealed with special sealants, pressure-sensitive tapes, or heat-sensitive tapes. The cross-sectional size of the air duct and the size of the wind pressure shall be followed by appropriate reinforcement measures. It has the advantages of noise reduction, heat preservation, fire prevention, moisture resistance, small air leakage, light material, easy construction, saving installation space, long service life, economical and applicable, etc.
Fiber fabric air duct: also known as cloth bag air duct, fabric air duct, fiber fabric air duct, fiber fabric air distributor, is the latest type of air duct, and is a flexible air distribution system woven from special fibers (Air Dispersion), is an air delivery end system that replaces traditional air supply pipes, air valves, diffusers, heat insulation materials, etc.
3. Performance comparison of four air ducts
3.1 Thermal insulation performance
Galvanized steel sheet air duct: the thermal conductivity is very large (60.4 W/m·K), and it has no thermal insulation performance, so an insulation layer and a protective layer must be added. It is difficult to ensure the insulation thickness at the flange of the air duct or there is no insulation, which will cause a cold bridge phenomenon, and the coverage uniformity of the insulation layer on the wall surface of the air duct is sometimes difficult to ensure due to insufficient installation clearance.
Inorganic FRP air duct: It has a large thermal conductivity (0.5W/m·K), has no thermal insulation performance, and must be additionally covered with an insulation layer and a protective layer. The characteristics of the insulation layer are the same as those of the galvanized steel sheet air duct.
Composite glass fiber board air duct: small thermal conductivity (0.029W/m·K at an average temperature of 24°C, 0.04W/m·K at 70°C), especially the composite aluminum foil cloth on the outside has a high heat reflection ability. Because the air duct wall is the insulation layer, the duct adopts mortise joint, T-shaped inner frame butt joint and iron sheet connection (or outer flange connection), so that all parts of the entire air duct are insulated evenly, without cold bridge phenomenon, and has good performance Thermal insulation performance.
3.2 Fire performance
Galvanized steel sheet air duct: non-combustible, but whether the insulation layer is combustible depends on the material, and non-combustible thermal insulation materials such as centrifugal glass wool are usually used.
Inorganic FRP air duct: same as galvanized steel sheet air duct.
Composite glass fiber board air duct: use non-combustible glass fiber cotton board as the base material, use flame-retardant adhesive, and compound aluminum foil cloth and glass fiber cloth on both sides of the base material, so the finished air duct is a non-combustible material, with Good fire performance.
3.3 Noise reduction performance
Galvanized steel sheet air duct: no noise reduction performance, a muffler and fabric expansion joints must be installed, and the muffler and fabric expansion joints must achieve the desired effect, and its setting position has certain requirements, which is difficult to achieve in actual engineering, making it difficult to guarantee the actual noise reduction effect . Moreover, secondary noise is generated when the wind speed is high, the length of one side is large and the reinforcement is not enough, or it is matched with a high-frequency fan.
Inorganic glass fiber reinforced plastic air duct: no sound attenuation performance, sound insulation performance is better than galvanized steel sheet air duct.Also must be equipped with a muffler and fabric expansion joints, just like galvanized steel sheet air duct, it takes up more space, and the effect of noise treatment is not ideal.
Composite glass fiber board air duct: its pipe wall is a porous sound-absorbing material, which has a good sound-absorbing effect on medium and high-frequency sound waves. It is a good tubular muffler and fabric expansion joints, which can eliminate primary noise and the secondary noise generated by the valve body, pipe fittings, etc. will become more effective with the extension of the pipeline, and the special muffler and fabric expansion joints can be omitted.
3.4 Moisture-proof performance
Galvanized sheet steel air duct: susceptible to moisture corrosion and rust, especially when transporting air with high moisture content. During the manufacture of the air duct, the galvanized layer at the bite of the iron sheet was damaged, so it is not easy to make up and do anti-corrosion treatment. Condensation will also occur at the place where the cold bridge occurs to corrode the pipeline, thus affecting its overall life.
Inorganic FRP air duct: restricted by the ratio of raw materials, its moisture-proof performance is poor in stability.
Composite glass fiber board air duct: no perishable materials and parts, the outer surface of the air duct is moisture-proof aluminum foil cloth, its moisture permeability is zero, but it has strong anti-corrosion ability, the water absorption rate of glass fiber board is not more than 2%; when the duct is in a humid environment for a long time, its sound attenuation and thermal insulation properties will not change. Because it is a porous material, it is necessary to prevent the inside of the pipe, the pipe end and the cut from being soaked in water for a long time.
3.5 Air leakage
Galvanized sheet steel air duct: When the total length of the air duct is less than 50m, the air leakage rate usually reaches 8% to 10%. When the total length of the air duct increases, the air leakage rate should increase appropriately. When the static pressure inside the pipe is 500Pa, the air leakage per unit area of the air pipe is 6mᶟ/h·㎡.
Inorganic FRP air duct: When the total length of the air duct is less than 50m, the air leakage rate usually reaches 6% to 8%. When the total length of the air duct increases, the air leakage rate should increase appropriately.
Composite fiberglass board air duct: the air duct is connected by slotting, mortise, and glue, and the joint is sealed with aluminum foil tape. The air leakage rate of the unreinforced air duct is basically zero, and the air leakage rate of the reinforced air duct is not more than 1%. Air leakage rate is not more than 2%. When the static pressure inside the pipe is 500Pa, the air leakage per unit area of the air duct is less than 1.8mᶟ/h·㎡.
3.6 Strength
Galvanized steel sheet air duct: high strength, strong static pressure resistance, must be reinforced according to regulations when the section size is large.
Inorganic FRP air duct: high strength, but relatively fragile, because of its heavy weight, it is not easy to handle, and it is easy to be cracked and damaged by collision. Due to the large self-weight, the wall thickness of the air duct increases rapidly when the side length of the horizontal plane is large, and the weight of the pipe wall per unit area increases greatly, which is prone to permanent damage.
Vertical deformation and settlement.
Composite glass fiber board air duct: It can meet the pressure bearing requirements of general ventilation and air conditioning. When the wind pressure is 500Pa, the deformation of the pipe wall is not more than 1%. When the wall thickness is 25mm, it can withstand 800Pa static pressure. If it needs to withstand greater pressure or the side length of the air duct is more than 630mm, it can be reinforced according to the wind pressure and design requirements, and the maximum wind pressure can withstand 1500Pa.
3.7 Weight
Galvanized steel sheet air duct: the bulk density is 7870kg/mᶟ, the weight per unit area is 10kg/㎡～16kg/㎡ (thickness of thin steel plate δ=0.5mm～1mm, including the weight of insulation layer and protective layer, including flange and hanging bracket The weight is 4kg～4.8kg).
Inorganic FRP air duct: the bulk density is 2100kg/mᶟ, and the weight per unit area is 11kg/㎡～23kg/㎡ (wall thickness δ=3mm～8mm, including the weight of the insulation layer and protective layer, including the weight of the suspension bracket 1.7kg).
Composite glass fiber board air duct: The bulk density is 64kg/mᶟ, and the weight per unit area is 2.8 kg/㎡ (wall thickness δ=25mm, including the weight of the suspension bracket 1.5kg).
3.8 Friction resistance
The inner wall of the composite glass fiberboard air duct is glass cloth, and the surface roughness is 0.2mm, which is slightly larger than the measured value of the galvanized steel sheet. Under the condition that the wind speed in the air duct is less than 15m/s, its resistance along the way is the same as that of the galvanized steel sheet air duct. Compared with no more than 7% (including the resistance increased by the reinforced struts in the air duct), the resistance along the way in the general air conditioning system ventilation duct only accounts for about 10% of the local resistance (basically the same as the local resistance of the galvanized steel sheet air duct ), so the increased ventilation resistance of the glass fiber duct compared with the Galvanized steel sheet duct is less than 1%, and the influence on the whole duct system is not obvious and can basically be ignored. The frictional resistance of the inorganic FRP air duct is greater than that of the galvanized steel sheet air duct, and is close to that of the composite glass fiber board air duct.
3.9 Shielding fiber capacity of glass fiberboard air duct
The inner wall of the air duct is composited with glass cloth, which has the ability to shield the dispersion of fibers. Under the condition of the wind speed in the pipe of 15m/s, the fibers on the inner wall of the air pipe will not fall off, which fully complies with the national hygienic standard and ensures the indoor air quality and environment.
3.10 Service life
Galvanized steel sheet air duct: Poor moisture resistance, which reduces the overall life of the air duct, and its life is generally 5 to 10 years.
Inorganic FRP air duct: heavy, difficult to carry, and fragile, vulnerable to cracks and damages caused by collisions, and prone to permanent vertical deformation and settlement, affected by environmental changes of dryness, humidity, high temperature, and low temperature; it is easy to cause its material is more fragile, cracked, and peeled. If the ratio of raw materials does not meet the standard, the phenomenon will be more serious, thereby reducing the overall life of the air duct, which is generally 5 to 10 years .
Composite glass fiber board air duct: light weight, corrosion resistance, anti-aging, easy to disassemble, repair and change pipelines, and the service life can be as long as 10 to 30 years.
1. Construction and installation of air ducts
Galvanized sheet steel air duct: the pipe is heavy, the production and installation period is long, and the change of pipe size and direction is labor-intensive. The insulation layer is installed on site after the air duct is installed, the process is cumbersome, and the insulation thickness at the air duct flange is not easy to guarantee or there is no insulation. There should be sufficient space for the installation and operation of the insulation layer around the air duct, otherwise the uniformity of the insulation layer coverage will be difficult to ensure due to insufficient installation clearance, and the appearance will not be beautiful. Adding a muffler and fabric expansion joints requires more space, and increases the difficulty and workload of installation.
Inorganic FRP air duct: The duct is bulky, not easy to carry, and has high strength, but it is relatively fragile, and it is easily cracked and damaged by collision. The production and installation period is long, and the change of pipe size and direction is labor-intensive and time-consuming. In terms of noise reduction and heat preservation, it is the same as that of galvanized steel sheet.
Composite glass fiber board air duct: the duct is light, and the installation speed is fast. Because the duct and the insulation layer are integrated, the installation procedure can be completed at one time, which is convenient for installation changes according to site conditions or design during the installation process, without affecting other processes. Compared with other materials, it can save the operating space of the insulation layer, and can save the ceiling clearance of 150mm~200mm. It has a beautiful appearance and is also suitable for surface installation. It can also be decorated with colorful paints, so as to achieve harmony with the surrounding environment. But because it is a non-rigid material, it should be handled with care to avoid man-made damage.
5.Market analysis of various air ducts
Galvanized steel sheet air duct: It is a traditional product with a wide range of uses. Its advantages and disadvantages have long been understood and recognized by the majority of users.
Inorganic FRP air duct: It is a new product. Because of its advantages of fire prevention, anti-corrosion and noise isolation, it once seized more than half of the air duct market. Some of the deficiencies in the industry have been understood, and the market share of inorganic FRP ducts has gradually shrunk.
Composite fiberglass air duct: It is a new product in recent years, because it has a major change over the previous products, as time goes by, it has changed from people’s ignorance, doubts, and wait-and-sees to the current cognition, affirmation and recognition. Large-scale promotion and application have been widely used in large cities such as Beijing and Shanghai. Under certain conditions and according to specific requirements, the fiberglass board can also be used as the lining of other pipes to make heat-insulating and noise-absorbing galvanized steel sheet air ducts or inorganic glass fiber reinforced plastic air ducts.
Post time: Mar-13-2023