Ventilation and air conditioning related equipment installation and air leakage test ----------------------------------------- ---------------------------------------
Ventilation and air conditioning duct production and installation of key learning
With the continuous improvement of the high-grade office and office environment, the air-conditioning system has become more and more popular in daily life. How to make the selected air-conditioning system play the best effect, in addition to the rationality of the design, the construction of air-conditioning ventilation project is also an important factor. As an important part of the air conditioning and ventilation engineering, the air duct has a direct impact on the installation quality and operating results of the construction quality. In many air-conditioning and ventilation projects, due to problems in the production and installation quality of air ducts, the air supply volume is insufficient, and the amount of air leakage exceeds the regulatory requirements, resulting in phenomena such as energy waste, lack of heat sources, and unstable operation of air-conditioning ventilation projects, all affecting the normal operation of air-conditioning. .
In the following, with reference to specific engineering examples of an air-conditioning ventilation project, the production and installation techniques of air ducts and common quality problems and corresponding countermeasures are introduced for reference by colleagues.
1. Duct assembly technology
A building is a comprehensive building that gathers guests, negotiates, conference centers, and exhibitions. It is located on the second floor underground and five floors above the ground. The second underground floor is a power distribution room, equipment room, and property management room. The air-conditioning of this building adopts two kinds of air-conditioning chilled water, one of which is 3.3°C~14.4°C, which is provided by an ice storage device for all air-conditioning unit of the building; the other is 7.8°C~14.4°C, and consists of a conventional cold water. The unit provides, supply wind coil and later development use. The ice storage system is set up according to the partial load ice storage method. The ice storage host and the ice storage tank are connected in series, and the host is upstream. The operating mode of the design conditions adopts the host priority mode, and the ice priority mode can be used most of the time. The ice-carrying capacity is a 25% ethylene glycol aqueous solution, which serves as the primary side of the cold source of the air-conditioning. The two-plate heat exchangers provide the building with 3.3°C air-conditioning chilled water. In the chilled water system, a 420RT conventional screw-type chiller is installed. In addition to the pre-cooling provided by the return water of the 3.3°C chilled water system, the unit also directly provides 7.8°C fan coil equipment. The air-conditioning variable air all-air-conditioning system adopts a low-temperature air supply method and serves the commercial area, conference center, and exhibition area. These systems send cooling air to the interior through the end of the air volume at the end of the room, which can solve the perennial cooling load in the commercial areas, conference centers, and exhibition halls. The air-conditioners in the front room and the basement equipment room of the staircase, and in individual offices, etc. are fan coiled. The assembly of the project air duct itself adopts a composite connection method, and the connection between the pipe sections adopts two connection methods of flangeless and flanged.
1.1 can not connect blue
Due to the fact that the air pipe can not be connected with joints with tight joints and good quality, the joints are light, the materials are saved, the construction process is simple, the man-hours are saved, it is easy to realize full mechanization, automatic construction, and the construction cost is low, so it is widely used. At present, there are dozens of types of wind pipes that can not be connected in blue form, and new forms are still emerging, but according to its structural principles can be divided into five kinds of sockets, cuttings, bite, tin flange and hybrid connection. The flangeless connection is mainly used for ducts with small side lengths, with C-shaped and S-shaped plug connections. The ducts of each floor above the second floor of the Songhu Building are of small size. The ducts with the length of less than 450mm are connected by C-shaped cuttings. The ducts with the length of more than 450mm and less than 1000mm are vertical S-cuts. After connecting, connect the ends of the cuttings and the air pipe riveted with a hollow rivet, and then apply sealant at the gap to ensure the tightness of the air pipe. The basic measures to improve the quality of wind passengers can not be linked to the construction quality are as follows:
(1) Strictly control the use range of each flangeless joint according to the specification requirements, such as the use range of “S†and “C†cutting inserts is that the long side of rectangular wind pipe is not more than 630mm, and the vertical bite mouth is not more than 100mm. The width of the 90-degree affixing angle should be consistent with the height of the standing gusset, and the 90-degree should be accurate. When the joint is connected to the hem, the pieces are stitched one by one in order, and the back is covered with square iron, so that the flange is flattened and the 90-degree line is straight.
(2) Strictly according to the wind pipe size tolerance requirements. If the misalignment of the mouth is obvious, the cuttings will be misplaced; if the mouth is caught in a large mouth, it will be unable to be fastened or the joints will be skewed or distorted. The cuttings cannot be deflected significantly, and the opening joints should be in the middle. No matter whether the cuttings or the pipe end cuffs should be accurately folded, the connection joints will be neat and tight.
(3) The sides of the four sides of the cuffs should be flush on one side, and the small ones can be folded out with a folding machine at a time. The cuffs should be equal in width along the entire extension line. This is also necessary when the duct connection is straight when the docking is installed.
(4) In addition to the iron flange spring clip (including the metal flange insert) in the installation of the docking surface plus seals, and other after the connection is applied to the outside of the seam sealant, seam cleaning before coating. Sealant can not be replaced with putty, lime paste, etc., apply air duct special plastic bags.
(5) The air duct installation hanger is set according to the specifications. After the air ducts are connected, the duct air leakage test shall be conducted according to the requirements of the specification class.
1.2 with flange connection
The connection between the two air ducts is accustomed to adopting angle steel flanges at home. The practice of labor-consuming materials has been extended for many years. The flange connection of the air-conditioning ducts of the building draws on foreign advanced technologies and processes, combined with their own actual conditions. , using the TDF and TDC connection method.
(1) The TDF connection is a self-flange of the two ends of the air pipe itself, and then the two air ducts are buckled by the flange angle and the flange clamp.
a. The four corners of the air duct are inserted into the flange corners;
b. Evenly fill the sealant around the flange surface where the air pipe is welded.
c. The combination of flanges, and insert the flange clips from the four corners of the flange;
d. 4 flange bolts;
e. Using a vise, clamp the flange clamp together with the two flanges;
f. The flange clamp is 1500mm away from the flange angle, with 4 flange clamps; the flange side is 900-1200mm long.
3 flange clamps; flange length 600mm, with 2 flange clamps; flange length below 450mm, use 1 flange clamp in the middle.
(2) The TDC connection is a plug-in duct flange connection. This method of connection is suitable for connections where the length of the large side of the air duct is between 1500-2500 mm.
a. According to the length of the four sides of the air duct, prepare four flange strips;
b. Insert four flange strips and four flange corners on each side of the air duct;
c. Check and adjust the leveling of the flange opening;
d. Flange strips and air ducts are riveted with hollow rivets;
e. Combination of two air ducts. The flange surface is evenly filled with the sealant, the two flanges are combined and inserted into the flange clamps, the bolts are tightened at the four flange corners, and finally the hand vise is used to clamp the flange clamp together with the two flanges.
f. For larger air ducts on the common floor, when the length of the large side of the air duct exceeds 2500mm, the angle flange connection is still used.
2, the detection of air leakage
In order to check the air leakage condition of the flangeless connection and TDF, TDC flange connection new technology and new technology, it is verified whether it meets the requirements of the national standard specification (GB50243-2002), and the wind pipe and TDF flange connected to the C-shaped cutting insert respectively. Connected air ducts, TDC flanged air ducts, and C-shaped, S-shaped, TDF, TDC mixed air ducts were tested for air leakage.
2.1 Test Methods
The duct test section to be tested is closed and tested using a Q89 duct air leakage tester. First, connect the test fan air supply hose and the air duct test section, and then connect a small hose in the air duct test section to the tilting pressure gauge on the tester, and then start the tester fan, so that the stepless adjustment The rotation speed of the fan is from slow to fast, and the pressure in the test section of the air duct is also increased. When the pressure is increased to the pressure required for the test, it is made stable. At this time, the amount of air leakage in the test section is equal to the amount of air added to the fan. The negative pressure reading is displayed directly on the tilt gauge.
Air leakage in the test section: Q=http://Html/fj-ziliao/F*a*P*p
In the formula: F — cross-sectional area of ​​fan ducts;
a - flow coefficient, winning 0.97 ~ 0.98;
P — negative pressure displayed by the tilt gauge;
P—air density, taking 1.293.
Then, according to the area of ​​the air duct in the test section, calculate the amount of air leakage per unit area.
2.2 Actual test results
(1) In case of C-shaped cutting inserts, the amount of air leakage is 4.5m3/(m2·h) when the sealant is applied.
(2) Joints of vertical S-shaped cutting inserts and C-shaped cutting inserts. When the sealant is applied, the amount of air leakage is 4.8m3/(m2·h).
(3) When the TDF is flanged and the seal is not applied with a sealant, the air leakage is 1.86 m3/(m2·h).
(4) C-shaped cutting inserts, vertical S-shaped cutting inserts, TDF flanges and TDC flanges are mixed and connected, and the air leakage is 1.95m3/(m2·h) when the sealers are not coated with sealant; In the case of the sealant, the amount of air leakage was 1.83 m3/(m2·h).
2.3 Standard Requirements
(1) National Standard "Code for Construction and Acceptance of Ventilation and Air Conditioning Engineering" (GB). The allowable air leakage volume for low pressure air ducts is 6 m3/(m2·h) or less.
(2) European Standard "European Air Conditioning Contracting Association Construction Standards" (DW/143), Low-pressure air ducts allow air leakage of less than 5.5 m3/(m2·h).
2.4 Actual test results
The central air-conditioning project of this building is a commercial comfort low-pressure air-conditioning. According to the test data, it is fully qualified if the seam of the air pipe itself is not coated with sealant. After the sealant is applied to the bite joint, the amount of air leakage from the air duct is less and the situation is better. The engineering volume of ventilation ducts for the project is about 50,000 m2, and the quality requirements are high. The progress of the main project is fast. According to the traditional small workshop production model, the company's total ventilation workers are not enough to cope with this project, because the wind pipe production process has been realized. Mechanization and automation have improved the professional production technology level and technical level, and promoted the improvement of product quality and production efficiency. Under normal circumstances, four workers of the wind pipe production line operate, and can produce square air duct semi-finished products of 1,000 m2 per day, which significantly reduces The cost increases economic efficiency. At the same time, the wind pipe processing production line uses the computer to loft and cut materials, cut reasonably, and the plate is fully utilized. According to calculations, it is possible to save 6% more material than the traditional production process. According to the calculation of the air duct for ventilation and air conditioning in this project, it is possible to save 7,800 m2 of galvanized sheet, about 40 tons, at 7,000 yuan per tonne, only for this engineering material fee. Save 280,000 yuan.
The air duct produced in the form of assembly line has stable quality, precise appearance, and uniform length specifications of the straight pipe. When assembled at the construction site, the interchangeability of the same specifications is good, the assembly is convenient, and the installation is quick. Taking the installation of the air duct on the second floor as an example, due to the TDF, TDC flange connection, and C-shaped cutting and vertical S-shaped cutting, the 12,000 m2 air duct used to require 20 workers for 122 days. Now, 20 workers have completed it in only 65 days.
3, wind control safety problems and prevention
3.1 Material does not meet quality requirements
(1) Phenomenon: The surface of the sheet is uneven and uneven in thickness. There are obvious indentations, cracks, blisters, scabs, and rust. The plane of the air duct sinks, and the side surfaces of the air duct bulge outwards, with obvious deformation.
(2) Hazard: When the system is running, the air duct leaks air, causing unnecessary air conditioning load loss and affecting the service life of the air duct. The surface of the air duct flutters and generates noise.
(3) Reason analysis: Before making the air duct, no quality inspection was performed on the materials used; there was no measurement of the thickness of the steel plate.
(4) Prevention and control measures: firstly check the material factory qualification certificate and material quality certificate, then check the appearance of the material; measure the thickness of the steel plate.
3.2 Inaccurate wind pipe angle, twist and elbow angle
(1) Phenomenon: The two opposite planes of the rectangular air duct are not parallel and the two end surfaces are not parallel; the folding angle is not straight; the diagonal lines are not equal; the bite mouth is not strict.
(2) Harmfulness: Will make the wind pipe connection force is not uniform, the wind pipe is not straight after installation, flange gasket is not tight, the system leaks air, causing air conditioning load loss, and shorten the service life; affect the wind pipe, The tuyere installation position is accurate.
(3) Reason analysis: The board blanking is inaccurate; the air ducts are parallel, and the length and width of the opposite sides are not equal; the widths of the mouths at the four corners of the air ducts are not equal; The size of the mouth seam is not the same; no corresponding reinforcement measures have been taken.
(4) Prevention and control measures: When the material is unrolled, it shall be strictly squared on the sheet material, the length and width of each sheet material and the diagonal line shall be checked to make their deviations within the allowable range; , should be the opposite side of the wind pipe two sheets of material together to verify the accuracy of the size; sheet metal bite reserved must be correct to ensure that the width of the mouth bite; bite joints in the four corners, manual bite joint When sewing, use a wooden hammer to first tighten the center of both ends of the bite, and then evenly press along the full length; implement the relevant provisions of the national standard "Code for the Construction and Acceptance of Ventilation and Air Conditioning Engineering".