The change of ventilation duct

Ventilation duct is an accessory product of buildings, few people study it. With the increase of air duct function, the ventilation duct has not only the requirements of ventilation intensity, but also has the functions of fire prevention, energy saving, environmental protection and easy cleaning. The use of ventilation ducts in China began in the 1940s. In the textile industry, in order to improve the quality of spinning and weaving, it is necessary to keep the set temperature and humidity in the workshop. The pipe conveying air with specific temperature and temperature was called air duct at that time. In the early days, the air duct was made of wood, and then iron sheet was used.

In the 1980s, glass fiber reinforced polyester duct (commonly known as FRP duct) appeared. Glass fiber polyester air duct is an organic material, which is resistant to water and gas corrosion and does not rust. It solves the shortcomings of galvanized iron sheet air duct that is easy to rust and has a short service life. It is widely used in textile factories.

As the glass fiber polyester air duct is a combustible material, once there is a fire due to short circuit or accidental fire, the polyester air duct will be ignited, which will spread to various workshops and cause fire. In this way, the combustible polyester duct caused the attention of the fire department. Code for fire protection design of high rise buildings (GB 50045-1989) stipulates that "the ventilation duct shall be made of non combustible materials". From then on, in addition to the strength requirements, the fire protection requirements were increased.

With the demand of building energy conservation, gb20189-2005 "design standard for energy efficiency of public buildings" has been implemented, which puts forward energy-saving design requirements for ventilation duct: thermal resistance value of general ventilation pipe is ≥ 0.74m2 · K / W, thermal resistance value of low-temperature air duct is ≥ 1.08m2 · K / W, which increases the energy-saving requirements for air duct.

In addition to the requirements of building energy conservation, the air quality in the building also began to attract more attention. Especially after SARS, the ventilation pipe is regarded as the channel of breeding bacteria and spreading diseases. GB 19210-2003 "air conditioning and ventilation system cleaning specification" has made provisions on the ventilation pipes in public places, adding the sanitary requirements of cleaning, cleaning and anti bacteria breeding.

Defects of galvanized iron sheet air duct

As we all know, galvanized iron sheet wind has several disadvantages, such as easy rusting, short service life, large ventilation noise, large air leakage, easy to produce hot bridge (cold bridge) due to external moisture damage.

1.1m2 iron sheet (0.1m2 loss) per m2 iron sheet, 2 m angle iron and 10 sets of bolts and nuts are used for the production, installation and consumption of air duct of iron sheet. The equivalent weight is: iron sheet 1.1m2 × 7.8kg/m2 = 8.58kg, angle iron 2m × 2.4kg/m = 4.8kg, 10 sets of bolts and nuts × 0.05kg/set = 0.5kg. The steel consumption per m2 of iron sheet air duct is 13.88kg, which is a large steel consumption.

Galvanized iron sheet air duct is easy to grow in humid environment, but its service life is only 7 years. According to the steel consumption of 13.88kg per m2 of air duct and the service life of 7 years, the annual consumption of steel per m2 of air duct is 13.88kg △ 7 = 1.98kg. In China, the use of 100 million m2 of iron sheet air duct is equivalent to the annual loss of 198 million kg steel due to rust corrosion.

According to the test of energy consumption, the production of iron sheet per m2 (7.8kg) consumes 20kwh. According to the weight of 13.88kg steel per m2 of air duct, the power consumption per m2 of air duct material is 42kwh. Using galvanized iron sheet to make air duct is more energy consuming.

The air leakage of galvanized iron sheet air duct is large, and the designer usually calculates it according to 10% air leakage coefficient. However, the thermal conductivity of galvanized iron duct is high, which requires external insulation, and the energy loss of external thermal bridge (cold bridge) reaches 5%. In this way, the energy loss of the iron sheet air duct can reach 15% by adding the air leakage loss and the heat bridge loss. According to the air volume of 20000m3 / h, the cooling capacity of 300kW and the use of air duct of 2000m2, the power consumption of each m2 of air duct per hour is 0.15kwh, 24h power consumption is 3.6kwh, and annual power consumption is 1296kwh. According to the loss of 15%, 1296kwh × 15% = 194.4kwh. The annual consumption of iron sheet air duct is 100 million m2, and the annual loss of electric energy is 19.44 billion kwh.

Under the action of wind, the wall of iron air duct vibrates, producing resonance sound and increasing noise. Noise is also a loss of energy. In order to reduce the noise, a muffler is added to increase the use cost of the air duct.

According to the existing problems of galvanized iron air duct, it can be seen that galvanized iron air duct is a large steel consumption, operation energy consumption and energy consumption loss. Galvanized iron sheet air duct is a product with backward technology, high energy consumption and low benefit. Therefore, it is imperative to replace galvanized iron duct with nonmetal air duct.

Characteristics of three mechanism glass magnesium composite plate air duct

The Ministry of construction [2007] No. 127 document issued the task of compiling the industry standard of machine-made glass magnesium composite plate air duct. The standard is edited by Zhejiang Tianren air duct Co., Ltd. The mechanical glass magnesium composite plate air duct is made of glass fiber reinforced material and magnesium oxychloride cement as cementitious material. The glass magnesium composite board is made on the two sides of the foam board with composite glass fiber and magnesium oxychloride cement, and then combined with the glass magnesium composite board to form the ventilating duct of the wind pipe.

The high strength machine-made glass magnesium composite plate air duct can meet all kinds of wind pressure requirements below 3000pa. Under 3000pa wind pressure, the air duct will not crack and leak. In 2003, the library of Hubei University adopted gm-ii Tianren composite duct produced by Zhejiang Tianren air duct Co., Ltd. (the representative product of machine-made glass magnesium composite plate air duct). The project is installed by China Construction Third Engineering Bureau and supervised by Beijing Pan Hua company. The installation and supervision units carried out the air duct pressure test on site. The air duct size of the sample is 400mm × 400mm × 1000mm (length), and both ends are closed. Add air pressure to the air duct of the sample. When the air pressure is increased to 1000Pa, stop pressurization (because the design pressure is 500pa, the design requirements have been met). One hour later, check the pressure, or 1000Pa, to show the sealing effect of the special adhesive.

After the purpose of pressure test is achieved, the product continues to carry out destructive test. When the pressure is increased to 15000pa, a piece of air duct plate of the sample air duct is cracked, and there is no crack in the adhesive bonding place. The special adhesive for glass magnesium composite air duct is made of oxychloride cement, which is the same material as the air duct plate. Therefore, the adhesive strength is high and the bonding strength is good. It will not crack even under the wind pressure of 15000pa. The strength of the machine-made glass magnesium composite plate air duct can meet all kinds of wind pressure requirements.

The construction is convenient, the machine-made glass magnesium composite board air duct is assembled at the construction site, and there is no flange connection, so the construction speed is fast and the cost is low. The gm-ii Tianren compound of Hubei University Library is 15000m2, which is basically completed in two months. The project manager of China Construction Third Engineering Bureau summed up three advantages of Tianren composite air duct. First, the equipment for making air duct is simple, which can be combined by hand-held cutting machine and painter's knife, and large and small air ducts. But the iron sheet air duct must need large-scale equipment such as shearing machine and molding machine to make air duct. Second, convenient handling. As long as the air duct board is moved to each layer, the large and small air ducts can be made in each layer. Third, the construction speed is fast. The installation of 15000m2 air duct is basically completed in two months, and the iron sheet air duct is impossible.

The insulation layer of glass magnesium composite board air duct is in the middle without external insulation mechanism, and both sides are protected by magnesium oxychloride cement board. It will not be damaged during construction and staggered operation. Therefore, the phenomenon of energy loss of hot bridge (cold bridge) will not occur. The air duct installed can not be ground and beautiful.

After pressure test of Tianren composite air duct in Hubei University Library, the wind pressure of 1000Pa is still 1000Pa after one hour. It shows that the air duct bonded with special adhesive has good sealing performance and no air leakage. The air leakage of the iron sheet air duct is large, and the designer designs it according to the air leakage coefficient of 10%.

The air duct can be cleaned, and the manipulator is allowed to enter the air duct. The inspection door is opened on the air duct wall, which is more convenient than the iron sheet air duct.

The glass magnesium composite board air duct is made of magnesium oxychloride cement. The chlorine salt has disinfection effect, and the surface of the air duct is treated with anti mold. The air duct wall will not produce mold, which is an environmental protection type air duct.

(IV) reasons for substitution

Magnesium oxide and magnesium chloride are the main materials of the glass magnesium composite plate air duct. 80% of the world's magnesium oxide ore is in China, with abundant reserves and low price. Magnesium chloride is a by-product of potassium salt and sodium salt industry, which is used as waste utilization of air duct materials. Low cost materials and waste materials are used to produce ventilation pipes instead of galvanized iron sheets. Its social benefits are very huge.

Taking 100 million m2 of galvanized iron sheet air duct used in China every year: after the replacement of machine-made glass magnesium composite plate air duct, 1.388 billion kg of steel can be saved every year (including angle iron and flange); according to 20 kwh power consumption of 7.8kg/m2 galvanized iron sheet, 4.2 billion kwh of steel production can be saved every year. The power consumption per m2 of machine-made glass magnesium composite plate air duct is 2 kwh, and 100 million m2 is 200 million kwh. The machine-made glass magnesium composite plate air duct can replace the iron sheet air duct, which can save 4 billion kwh annually.

The strength is higher. Some people think that the iron air duct looks strong, and they worry about the strength and durability of the machine-made glass magnesium composite plate air duct. In fact, the service life of machine-made glass magnesium composite plate air duct is longer than that of iron sheet air duct, which is no less than 20 years, and its strength is higher. Magnesium oxychloride cement is an inorganic material, which does not age. Only weathering can affect the strength of air duct. However, the indoor use of air duct does not have weathering conditions, just like the service life of ordinary cement. In addition, the strength and wear resistance of magnesium oxychloride cement are 3 times higher than that of ordinary cement, which ensures the service life of machine-made glass magnesium composite plate air duct.

The machine-made glass magnesium composite plate air duct is a frame structure with bearing capacity of more than 1000N, and its anti deformation ability is much higher than that of iron sheet air duct. It fully meets the requirements of air duct strength under the comprehensive action of pressure, air flow and fatigue. The adhesive joint of the air duct composed of air duct sheets is L-shaped structure, and the bonding area is equal to twice of the thickness of the air duct plate. The tensile force and shear force are formed. The experiment of Hubei University Library has proved that there is no crack in the bonding joint under 15000pa wind pressure. In addition to the high bonding strength of the special adhesive, L-type bonding structure is also an important guarantee.

The air leakage of energy-saving iron sheet air duct reaches 10%, the energy loss of cold and hot bridge is 5%, and the total energy loss is 15%. The machine-made glass magnesium composite board air duct is bonded with special adhesive, basically no air leakage. The air duct does not need external insulation, and the energy loss is small, which can reduce the energy loss by 13% at least. The annual power consumption of 1296kwh / m2 × 13% = 168.48kwh/m2. Based on the annual use of 100 million m2 of glass magnesium composite air duct, the annual operation energy saving of air duct is 16.848 billion kwh, and 1 / 8 of air duct operation cost is saved for users.

The installation is more convenient, the iron sheet air duct flange increases the air duct height and reduces the indoor clearance height. The machine-made glass magnesium composite air duct adopts non flange, counterpart, longitudinal and dislocation connection, which not only increases the indoor clearance height, saves flange, but also is beautiful.

The service life of the iron sheet air duct is longer than 7 years in wet environment and more than 15 years in dry environment, and the average service life is 11 years. The service life of glass magnesium composite air duct is more than 20 years, nearly twice as much as that of iron sheet air duct, and the investment cost is saved by 50%. Zhejiang Tianren air duct Co., Ltd. has been producing ventilation duct with magnesium oxychloride cement for 18 years. The inorganic glass fiber reinforced plastic air duct produced 18 years ago is still in use, which proves the durability of glass magnesium air duct. Ningbo Youngor Group used Tianren composite air duct in 2003. The largest section of air duct is 6000 × 2800mm. It has been running for more than 4 years without any quality problems. Users are satisfied.

The cost and installation cost of machine-made glass magnesium composite plate air duct is lower than that of galvanized iron sheet air duct. Compared with iron sheet air duct, the project cost can be saved by 10% - 15%. According to the calculation of saving 15 yuan / m2, the project cost of 100 million m2 air duct project can be saved by 1.5 billion yuan.

Table 1 performance comparison of manufactured glass magnesium composite plate air duct and galvanized iron sheet air duct