Fabrication and Installation of Large Air-Conditioning Ducts

The crackle of air ducts leads to improper connection of air ducts, air outflow affecting the effects of air conditioners.

Related to the fabrication control of large-scale air conditioners and their installations, the below-delivered aspects are identified.  

1. Raw Materials

Designing of an air duct takes flex force more than 1.8 Mpa, thicknesses of 2.6 mm for a heat isolated duct, thicknesses within 1.8 mm for a non-isolated duct.

To be sure in the reliability of a material applied in the fabrication, in the efficiency of the whole process, selected brands must be approved by supervisors and owners to get assured of proper productivity and repute of the quality.

Each entry material has to be rigorously and thoroughly checked according to the procurement verification process to be certain about the excellence and reliability of the used materials.

2. Cutting of Sheets.

Sheets must be aligned prior to the cut.

The main lines: direct angular lines, vertical bisectors, collateral lines, angle bisectors, direct bisectors, circular bisectors and so on.

The deployment technique adopts methods of the parallel lines, radiation, and triangular lines.

In accordance with the various geometrical forms and technical characteristics of the design drawing and large-volume drawing, each line is deployed separately.

Check the cut suitability of sheets to escape errors, use a manual cutter in accordance with the scribe shapes.

 While cutting, do not allow the mechanic roller to fall into the gap.

No tool or item is allowed in the top knife carrier.

Do not step upon the pedal in the adjustment process of sheets.

If static vibration shears are used, steel plates should be held by hand. Hands should be kept off the blade at least 5 cms. 

The shears should be used with uniform strength.

The cut lines are upright, and the errors in diagonal lengths of ducts must not surpass 0,5 mm.

The depths of step lines are within 18-21 mm, the cut line should appear at 90-degree angularity making the joint angularity possible to 90 degrees.  

The upright tube part of rectangular ducts should be of great accuracy, The angular lines must be direct.

The 4 ending sides of sectional ports of air ducts (wyes, elbows and so on) must appear upon the same upright level as the central part of the tube.

Put numbers on each board to make use while assembling.

Air Conditioning Ducts
Air Conditioning Ducts

3. Assembly of Ducts

To meet the designing needs, to provide excellence in it and facilitation for the supervisors of the workshop and owner check-up, departments of design arrange the processing of ducts.

1. Preparation of particular glue

This glue is featured with reliable connections suitable for the assembly of air ducts. It is resistant to burns, watertight, convenient for use, proper for the materials of air ducts.

This particular glue consists of powder and fluid, the ratio of which is 10:9. Electric mixers should be used to stir the glue. It must be slightly fluid, not extremely dry or thin.

2. Process of Assembling (straight pipes)

2.1 First, cut the stepped heat-insulating coat of the lateral panel through knives, carefully trim it to provide leveled location for the step.

2.2 The particular glue should be applied to the steps of the lateral planes. Provide even and full glue application. The extra suspension should be removed while joining the top and bottom slabs.

2.3 The lower slab must be placed on group support.

Inset the left-side and right-side slabs on the ridge of the lower panel move 100 mm from the lengths of the top and bottom panes. Next, insert the top pane between the left-side and right-side panes.

Then tie the newly assembled ducts tightly together through straps. The distance between the straps is usually around 600 mm. Each corner must be defended by angular steel. Angular steels are pre-coated with mold lubricant. The latter consists of 1 kg saponified oil, 5 kg water, a little diesel oil. To eliminate the effects brought about by wet extension as well as a dry shrink of ducts, if the continual lengths of the direct section are above 15 m, it is necessary to install a compensator.

The internal angularity of the four tied ducts is 90 degrees. The extruded adhesive should be removed, the gaps should be filled to eliminate the deformity of ducts and to provide efficient splice for ducts.

Take away the straps and pulp leftovers off the butt joint, dependent on the suspension hardened condition. In the case of extreme solidification, the removal of the suspension remnants becomes hard. In case of the insufficient hardening strengths, the air ducts tremble to influence the bond strengths. The straps must be removed within the permitted time, take off the remaining suspension and carefully inspect the shakes of the duct. Typically, the surrounding temperatures are 10-20 degrees for a 24-hour period, more than 0 degrees for a 48-hour period and less than 0 degrees for the 72-hour period.

The fabrication is carried out in the wintertime, in severe conditions, so, naturally occurring cooling affects the fabrication process more or less. It is preferable to apply the central layer and heat methods to facilitate concretion. Assemble the air pipes for the connection in the room, close each door and window. Install an electrical heat inside and switch them all through the day to raise the temperatures in the room.

Thanks to the following arrangements, the temperatures will increase from 11 degrees, and the hardening duration of the ducts will change from a 72-hour-long period to 24-hour-long, which significantly reduces the curing duration and ensures effectiveness in the fabrication process.

3. Fabrication of attachments of the same cross-sections.

Shear duct plates in accordance with the sizes of the drawing, and forty-five deflection angularities in the wind directions.

After folding each elbow and the 3 heads in half, the inner expulsion technique is applied rather than the outer disclosure one. This implies cutting a V-shape stitch on the inner side of the plate while holding the plate in half. The middle froth should be removed, then suitable proportions of adhesive have to be applied. Next, the sheets must be twisted in half (it is better to squeeze out only a little of the adhesive). The lateral pane is sheared in shapes of stairs. Apply adhesive to them and fix them through bindings. Remove the adhesive leftovers, fill each gap, harden in a smooth place.

4. Duct Lifting

Installation of a duct hanger and support.

For the reliability of large air pipes, the space from one boom to the other must not surpass 2.0 m. The beams are composed of 50×50×5 mm angular steels, hangers are composed of Ф10 round sheets of steel and the dowels are attached to the supporting structures. 

Enhancing arrangements for a large air duct.

Air Conditioning Ducts
Air Conditioning Ducts

It is possible to strengthen air pipes in the fabrication and setting process.

If the long sides of air ducts are more than or the same as 800 mm or no more than 1250 mm, there will need to implement measures of strip strengthening. This means 25×40 mm strengthening strips should be attached to each corner of the air duct inner side, the application of the adhesive must be thick and without seams, The lengths must not differ from those of ducts. If the duct longer side exceeds 1250 mm, a stiffener is applied, which implies a connection between supporting columns and the air duct top and bottom slabs. Supporting columns use Ф10 screws and are attached to the top and bottom slabs of air ducts through nuts. A silicon-magnesium sheet of 80×80×5 mm is applied as a kind of strip upon the inner and outer sides of the top and bottom slabs, plastic insulating covers are used from the outer side. The between-rib space should not exceed 1.5 m.

Air Conditioning Ducts
Air Conditioning Ducts


The air duct must be lifted after complete solidification.

A lifting duct might be linked with the ground, then lifted to its position. The connection link must not surpass 10 m., otherwise, fractures can be caused. The air duct is possible to hoist through chain blocks and pulleys. The lifting is carried out step by step.

1. Choose 2 secure hoist spots upon the beam-columns in accordance with each condition of the area. Having done this, you can suspend chain blocks and pulleys.

2. Air ducts should be tied with hemp ropes, typically 2 bonds are made at ¼ from either end. Avoid tying the ropes right to the ducts. Provide cushions of mild materials for the points at which hemp ropes contact the duct corners to escape deformities caused by ropes.  

3. While lifting, one is not allowed to be beneath the air duct or step on it. As soon as the duct is lifted within 200-300 mm, thoroughly inspect the tension points of blocks, pulleys as well as ropes binding the air ducts, get certain about the security of the buckles and the proper gravity core. Go on lifting in case no error exists. For a long duct, lifting speeds must be synchronized to avoid deformity caused by extremely large tension on the central duct.

Air Conditioning Ducts
Air Conditioning Ducts

4. After the ducts rise to the carcass heights, the hanging portion of the carcass must be wrapped so as not to puncture the duct while lifting, which will damage the protective coating, the insulating covering as well as the air leak.

5. When the duct is finally mounted upon supports or hangers, link each tray and boom, be sure about the stability of the duct prior to untying the cable.

6. The lifted ducts must be exposed to splicing timely. They should not be shaken while being spliced. Use 2 wood boards of 1000 × 200 mm to stand on to avoid the tension growing in the space and to provide secure advancement.

7. Remove the residual adhesive when it is hardened, fill each gap timely. After the entire solidification of the adhesive, the ducts are checked through the control device, when they are approved, aluminum foil tapes can be attached.

8. Implement all the required measures to protect the finished products in the aftermath of fabrication. Attach labels “Care about the protection of finished products” in noticeable places to draw the staff`s attention to this and stick to it.