Explain the production and installation technology of ventilation and air conditioning ducts?

With the continuous improvement of high-end office buildings and office environments, central air-conditioning systems have also been widely integrated into daily life. How to make the selected central air-conditioning system achieve good results? In addition to the rationality of the design, the construction of the air-conditioning and ventilation project is also a very important part. The production and installation of air ducts is an important link in the air conditioning and ventilation system. The quality of its construction directly affects the installation quality and operating results of the system. Due to problems with the quality of air duct production and installation, the air supply volume is insufficient and the air leakage volume exceeds the specification requirements, resulting in energy waste, insufficient heat sources and unstable operation of air conditioning and ventilation projects, etc., which greatly affects the normal operation of air conditioning.

This article summarizes my many years of experience in ventilation and air-conditioning project construction, and combines the specific engineering examples of the ventilation project of a five-star hotel I participated in in the past to introduce the production and installation technology of air ducts and common quality problems and corresponding Countermeasures.

Air duct assembly technology

A hotel project is located on the south side of Chang'an Street. It is another landmark building along Chang'an Street undertaken by our company. It is a comprehensive five-star hotel integrating accommodation, catering, conferences and entertainment. There are twenty-five floors above ground and three floors underground. The second and third underground floors are garages, and the air-conditioning equipment floor is located on the first underground floor. Central air conditioning system cold source: The engineering cooling load is 6000KW, and three centrifugal chillers are selected, with a single cooling capacity of 600PT. The refrigeration machine room is located on the underground floor. The cooling tower is located on the roof of the 25th floor of the building. Chilled water temperature is 7/12℃, cooling water supply and return temperature: 32/37℃. Heat source: Heating is provided by the hotel's original heating station, and the heat exchange station is located on the underground floor. The heat medium used for air conditioning is: 60℃-50℃ hot water, manually switched between winter and summer. Thermal load is 4800KW. Air-conditioning water system form: The cold source side of the air-conditioning water system is a constant flow system, and the load side is a variable flow system. The air-conditioning hot and cold water system is equipped with separate pumps for winter and summer, a two-pipe system, and an expansion water tank device is used for system expansion and constant pressure. Fan coil units and air conditioners are equipped with dynamic balance valves to control water volume. Air-conditioning system form: According to the building's use function, this project mainly adopts a full air-conditioning system and a fan coil plus fresh air system. The fan coil unit adopts a horizontal high static pressure type with air box, and the indoor temperature controller has three levels of adjustment. The return air outlet is equipped with an aluminum alloy filter. The exhaust air from the corridor is recycled through the full heat recovery fresh air ventilation unit located on the roof.

1 Assembling the air duct

The air duct itself in this project is assembled using a composite connection method, and the connections between the pipe sections are flangeless and flanged.

Two connection methods.

1.1 No flange connection

Because the air duct flange connection has tight joints, good quality, light joint weight, material saving, simple construction process, time saving, and easy to realize full mechanization , automated construction, low construction cost and many other characteristics, it has been widely promoted and applied. At present, there are dozens of flangeless connection forms for air ducts, and new forms are constantly emerging. However, according to their structural principles, they can be divided into five types: socket, insert, bite, iron flange and hybrid connection. Flangeless connections are mainly used for air ducts with smaller side lengths, including C-shaped insert connections and S-shaped insert connections. After connection, use hollow rivets to rivet the end of the insert and the air duct, and then apply sealant to the gap to ensure the tightness of the air duct. The basic measures to improve the construction quality of air duct flangeless connections are as follows:

(1) In accordance with the specification requirements, strictly control the use range of each flangeless joint, such as "S" and "C" shapes

The use range of inserts is that the long side of rectangular air ducts is not larger than 630mm, and the vertical bite is not larger than 100mm. The vertical bite is 90 degrees

The width of the sticking angle should be consistent with the height of the vertical bite, and the 90 degrees should be accurate. When the interface joint is connected to the flange, it should be struck piece by piece in sequence

and tied on the back Pad it with square iron to make the flanged surface flat and the 90-degree line straight.

(2) Strictly follow the duct size tolerance requirements. If the misalignment of the opposite ends is obvious, the inserts will be inserted sideways; the small opening will fall into the large opening, causing the joint to be unable to be fastened or the joint to be skewed and twisted. The cuttings cannot be obviously skewed, and the opening seam should be in the middle. Whether the cuttings or the pipe end are flanged accurately and tightly, the joints will be neat and tight in the future.

(3) The four sides of the flanged pipe should be flush with one surface. The small tube can be folded out with a square folding machine at one time. The flanged pipe should be equal on the entire extension line.

Width. This is also necessary to ensure that the air duct interface is straight during installation and docking.

(4) Except for iron flange spring clips (including iron flange inserts) with sealing gaskets on the installation interface, most of the others

are outside the joint after the connection is completed. Apply sealant and clean the seams before applying glue. The sealant cannot be replaced by putty, lime paste, etc., and special plastic sealing bags for air ducts should be used. The sealing of air ducts should be mainly based on the sealing of plate connections. Sealant caulking and other methods can be used for sealing. The performance of the sealant should meet the requirements of the use environment, and the sealing surface should be located on the positive pressure side of the air duct.

(5) The supports and hangers used for air duct installation shall be set up according to the specifications. After the air duct is connected, the air leakage test of the air duct should be carried out according to the specification level requirements.

1.2 Flange connection

For the connection between two sections of air ducts, angle steel flanges are used in China. This labor- and material-consuming method has been used for many years. In practice, TDF and TDC connection methods are generally used.

(1) TDF connection is that the two ends of the air duct itself are flanged, and then the two sections of the air duct are connected by using flange angles and flange clamps.

a. Insert the four corners of the air duct into the flange corners;

b. Fill the flange surface evenly with sealant around the edge of the air duct;

c. Assemble the flange and insert the flange clamp from the four corners of the flange;

d. Tighten the bolts at the four flange corners;

e. Clamp the flange clamp together with the two flanges with a hand vise;

f. If the distance between the flange clamp and the flange angle is 1500mm, use 4 flange clamps; If the side length is 900-1200mm, use 3 flange clamps; if the flange side length is 600mm, use 2 flange clamps; if the flange side length is less than 450mm, use 1 flange clamp in the middle.

(2) The TDC connection is a plug-in duct flange connection. This connection method is suitable for connections where the length of the large side of the air duct is between 1500-2500mm. Generally divided into the following categories: according to the length of the four sides of the air duct, prepare 4 flange strips respectively; insert 4 flange strips and 4 flange corners on the four sides of the air duct; check and adjust the flatness of the flange mouth ; The flange strip and the air duct are riveted with hollow rivets; the combination of two sections of air duct. Fill the flange surface evenly with sealant, assemble the two flanges and insert the flange clamp, tighten the bolts at the 4 flange corners, and finally use a hand vise to clamp the flange clamp together with the two flanges. For larger air ducts on the first floor of the building, when the length of the large side of the air duct exceeds 2500mm, the angle steel flange connection method will continue to be used. The smoke prevention and exhaust air ducts are all designed to be connected with angle steel flanges.

Detection of air leakage in air ducts

In order to check some air leakage conditions of new technologies and processes of flangeless connection and TDF and TDC flange connection, and verify whether it meets the national standards and specifications According to the requirements, air leakage tests are conducted on C-shaped insert connected air ducts, TDF flanged connected ducts, TDC flanged connected ducts, "C"-shaped or "S"-shaped and TDF and TDC mixed-connected ducts.

1. Test method

Enclose the test section of the air duct to be tested, and use a Q89 air duct air leakage tester to conduct the test. First connect the tested fan supply hose and the air duct test section, then lead a small hose from the air duct test section to connect it to the tilt pressure gauge on the tester, and finally start the tester fan to make the stepless Adjust the fan speed from slow to fast, and the pressure in the test section of the air duct will increase accordingly. When the pressure rises to the required test pressure of 500Pa, stabilize it. At this time, the air leakage volume in the test section is equal to the fan The supplementary air volume displays a negative pressure reading on the tilt pressure gauge.

Air leakage volume in the test section: Q=F*a*P*p

In the formula: F - cross-sectional area of ??the air supply pipe;

a - flow coefficient , generally 0.97 ~ 0.98;

P - the negative pressure displayed using a tilt manometer;

p - the density of air, generally 1.293.

The air leakage per unit area is calculated based on the area of ??the test section air duct.

2. Test results

C-shaped inserts, when coated with sealant, the air leakage volume is 4.5m3/(m2?h); vertical S-shaped inserts, C-shaped inserts When the joint joint of the insert is coated with sealant, the air leakage volume is 4.8m3/(m2?h); when the TDF flange connection is not coated with sealant, the air leakage volume is 1.86m3/(m2?h) ; Mixed connection of C-shaped inserts, vertical S-shaped inserts, TDF flange and TDC flange. When the bite mouth is not coated with sealant, the air leakage volume is 1.95m3/(m2?h); when the bite mouth is coated with sealant Down, the air leakage volume is 1.83m3/(m2?h).

2.3 Standard Requirements

According to the national standard "Code for Construction and Acceptance of Ventilation and Air Conditioning Engineering" (GB50243-2002), the allowable air leakage of low-pressure air ducts is less than 6m3/(m2?h); Europe According to the standard "Construction Standard of the European Air Conditioning Contractors Association" (DW/143), the allowable air leakage of low-pressure air ducts is less than 5.5m3/(m2?h).

Common air duct safety quality problems and prevention

1. Materials do not meet quality requirements

(1) Phenomenon: The surface of the board is uneven, the thickness is uneven, and there are Obvious indentations, cracks, blisters, scarring and corrosion; the plane of the air duct sinks, the sides bulge outward, and there is obvious deformation;

(2) Hazardousness: When the system is running, The air duct leaks, causing undue air conditioning load loss and affecting the service life of the air duct; the surface of the air duct vibrates, causing noise;

(3) Cause analysis: Before making the air duct, conduct inspection on the material The quality inspection is not strict; the thickness of the steel plate is not enough;

(4) Prevention and control measures: first check the material factory certificate and material quality certificate, then check the appearance of the material; measure the thickness of the steel plate. The main materials used such as plates and shaped steel should have factory certificates or quality appraisal documents. The materials, varieties, specifications, performance and thickness of metal air ducts should comply with the design and current national product standards. The thickness of the steel plate or galvanized steel plate shall not be less than the relevant regulations. The surface of the galvanized steel plate shall not have defects such as cracks, scars and watermarks, and there shall be crystallized patterns on the galvanized layer.

2. The warping, twisting and elbow angles of the air duct are inaccurate

(1) Phenomenon: The surface of the air duct is uneven; the diagonals are not equal; adjacent surfaces are not perpendicular to each other ; The two opposite surfaces are not parallel and the planes of the two pipe ends are not parallel;

(2) Harmful effects: It will cause uneven stress on the air duct connection, the air duct after installation will not be straight, and the flange will If the gasket is not tight, the system will leak air, resulting in air conditioning load loss and shortened service life; affecting the accuracy of the installation positions of air ducts and air outlets;

(3) Cause analysis: Inaccurate placement of plate blanks; air ducts The two pairs are not parallel, and the length and width of the opposite surfaces are not equal; the bite widths at the four corners of the air duct are not equal; the bite seam is set in the wrong position, and the manual bite seam force is different; no corresponding reinforcement measures are taken; The angle of the angle steel air duct flange is less than 90°;

(4) Prevention measures: When unfolding and blanking, the angle of the sheet should be strictly controlled, and the length, width and diagonal inspection of each sheet should be lines, so that their deviations are controlled within the allowable range; the bite width and allowance are determined according to the thickness of the board and should meet the requirements of relevant regulations; after blanking the sheet, the two sheets on the opposite side of the air duct should be overlapped Get up and check the accuracy of the dimensions; the reserved size for the bite of the sheet must be correct to ensure that the width of the bite is consistent; the bite seams are located at the four corners. When closing the joints manually, use a wooden hammer to center the two ends of the bite first The parts are tightened, and then evenly pressed along the entire length; the folded or rounded steel plates are seamed using a seaming machine or manually. When operating, use even force and should not be too heavy. The single and double mouths are firmly interlocked, without cracks or half-bites. Implement the relevant provisions of the national standard "Code for Construction and Acceptance of Ventilation and Air-Conditioning Projects". Strictly control the entry angle steel to ensure the angle. At the same time, spot welding is first performed during welding, and then full welding is performed after adjustment to ensure that the size and angle of the angle steel flange meet the specification requirements. Air duct reinforcement: Reinforcement measures should be taken if the diameter of a circular air duct is greater than or equal to 80mm, and the length of its section is greater than 1250mm or the total surface area is greater than that of If the single-sided flat area of ??the low-pressure air duct is larger than that of the medium- and high-pressure air ducts, reinforcement measures should be taken.

3. The production quality of air duct accessories is poor, the air leakage is large, and the appearance is ugly

(1) Phenomenon: tees, elbows, reducers and back-and-forth in rectangular air ducts The gaps at intersections and joints during bending are too large and not dense;

(2) Harmful effects: It will cause the air duct to be loose, the system to leak, resulting in air conditioning load loss, and some even cause air flow noise in the duct Increase;

(3) Cause analysis: The board blanking and setting out is complicated, and the staff has inaccurate grasp of the process; the air duct blanking error is large, and the air duct bite is not dense; the processing technology is rough, Failure to strictly follow the construction process;

(4) Prevention and control measures: Construction personnel are required to be familiar with the construction process of air duct accessories, and mass production can only be carried out after the samples are qualified. Inspection of intersections and interfaces is strengthened, and the air ducts are Special sealant treatment. The seams between the air duct and the accessories should be tight and the width should be consistent; the folded corners should be straight and the arcs should be uniform; both ends should be parallel. The air duct has no obvious twists or warping angles; the surface should be smooth, with unevenness no greater than 10mm;

4. The air duct passes through the firewall incorrectly

(1) Phenomenon: Ventilation and air conditioning system When the air duct passes through the firewall of the fire protection zone, fireproof materials are not used in accordance with the requirements of the regulations;

(2) Harmfulness: It fails the acceptance inspection and does not comply with the fire protection regulations. In the event of a fire, it passes through the fire protection zone through this place. , expand the fire area and make the fire protection zone lose its function;

(3) Cause analysis: The sealing gasket of the ventilation and air conditioning system requires flame-retardant B1 grade sealing material. When passing through the fire protection zone, both sides Non-combustible materials must be used within the 2M range. The requirements of the fire protection zoning are not considered during construction, and the construction is uniformly carried out in accordance with the requirements for ventilation and air conditioning ducts;

(4) Prevention measures: Construction managers should pay attention to the air ducts passing through the fire protection zoning. Provide timely guidance according to different requirements to prevent unnecessary rework. This article combines specific projects to compare several common connection methods of air ducts used in ventilation and air conditioning systems, and conducts a quantitative analysis through air leakage tests. The quality problems that are likely to occur during the construction of air ducts, their prevention and control methods, and matters needing attention are put forward. Air duct production requires attention to detailed quality management and strict control to achieve first-time quality and prevent unnecessary rework, which will help reduce production costs and improve overall benefits.

4. Tightness test after air duct installation

After the air duct system is installed, it must be inspected for tightness and must pass the test before it can be handed over to the next process. The tightness inspection of the air duct system mainly focuses on the main and main pipes. On the premise that the processing technology is guaranteed, the low-pressure air duct system can be detected by the light leakage method. Medium-pressure air ducts should be tested for air leakage in strict accordance with the requirements of construction specifications.

After the air duct system is installed, tightness inspection should be carried out according to the system category. The tightness inspection of the air duct system should meet the following requirements:

(1) Low-pressure system air duct The strictness inspection shall adopt random inspection, with a random inspection rate of 5% and shall not be less than 1 system. On the premise that the processing technology is guaranteed, the light leakage method is used for detection. If the test fails, the air leakage volume test should be carried out according to the specified sampling rate.

(2) For the tightness inspection of the air duct of the medium-voltage system, after passing the light leakage test, the system air leakage test shall be randomly inspected. The random inspection rate shall be 20%, and shall not be less than 1 system.

(3) The systems to be randomly inspected for system air duct tightness inspection shall be deemed to have passed if they are all qualified; if any are unqualified, the sampling inspection shall be doubled until all are qualified.

Light leakage method detection: The tested air ducts are tested in sections, and the sampling rate is 50%. The number of light leakage points per 10m of low-voltage system air ducts should not exceed 2, and the average light leakage points per 100m should not be more than 2. There should be more than 16 points; the air duct should have no more than 1 light leakage point per 10m, and the average light leakage point should not exceed 8 per 100m. If there is any light leakage from the seam during the test, it should be sealed with glue.

Conclusion

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 air leakage exceeds the specification requirements, resulting in energy waste, insufficient heat sources and Unstable operation of air conditioning and ventilation projects and other phenomena will affect the normal operation of air conditioning. Therefore, the production and installation technology of air ducts and corresponding prevention and control measures are extremely important for the quality control of ventilation and air conditioning.

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