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Ventilation Ducts

Ventilation Ducts


Ventilation duct occupies a more important position in ventilation and air conditioning. It has a large construction area, a long construction period, and a relatively large proportion of the total cost. For budgeting work, the amount and price of ventilation ducts will consume a lot of time and energy from budget staff. Therefore, we must be familiar with the relevant regulations.


Section 1 Explanation of terms:

1. Air vents air intake and exhaust ducts made of brick, concrete, slag gypsum board, and wooden materials are generally constructed by civil engineering teams and do not belong to the scope of installation projects.

2. Air duct round or rectangular pipe made of sheet metal, polyvinyl chloride sheet or glass fiber reinforced plastic sheet. Phenolic series composite air ducts include: double-sided aluminum foil composite phenolic ducts, single-sided color steel phenolic ducts, double-sided color steel phenolic ducts, galvanized embossed phenolic composite ducts, etc.

3. Pipe fittings pipe components that connect pipes of different pipe diameters or different directions. Pipe fittings include elbows, tees, crosses, reducers, sky-circle, flanges, guide vanes, etc.

4. Guide vane a partition plate installed inside the air duct to reduce the influence of turbulence, noise and pressure drop. According to specifications, when the size of duct elbow A is greater than or equal to 500mm, guide vanes should be provided. The area of guide vanes can be calculated by formula method or look-up table method. Because the general construction drawings do not give detailed drawings of the guide vanes, we mostly use the look-up table method for calculations.

5. Canvas interface It is used for the connection between the inlet and outlet of the fan and the air duct. Those who use artificial leather instead of canvas shall not be converted.


Section 2 Three major elements of duct production and installation:

In the production and installation of the air duct, the three elements of the interface form of the air duct, the thickness of the steel plate used for the air duct and the cross-sectional size of the air duct are determined, and the cost of the air duct is also determined. Therefore, these three elements are also called the three elements.

1. The interface form of the air duct

There are two types of joints for the air duct: welding and snapping (riveting is relatively less used, and it has been comprehensively considered within the quota, so it will not be introduced separately).

Bite: Bite is a connection between ducts or steel plates. It uses the folding of the steel plate to realize the connection. Common forms of bite are: single bite, vertical bite, corner bite, joint angle bite, and snap bite. Among them, the splicing of the plates and the circular duct can adopt a single bite, the circular duct can adopt a vertical bite, and the rectangular duct or accessories can adopt a corner bite, a joint angle bite, and a snap-type bite.

The interface form is determined in principle according to the design regulations. If there are no regulations in the design, it can be selected according to the following principles.

(1) When the thickness of the steel plate is less than or equal to 1.2mm, snapping can be used;

(2) When the thickness of the steel plate is more than 1.2mm, welding can be used;

(3) If the duct is made of galvanized steel sheet, biting or riveting shall be adopted.


2. The thickness of the steel plate

The thickness of the steel plate for the production of the thin steel plate air duct shall in principle be subject to the design specification. If the design is not specified, it can be selected according to the national standard (GB50243-2002).


3. The cross-sectional size of the duct

Commonly used air duct cross-sectional dimensions are rectangular and circular. The dimensions on the drawing are indicated. The outer diameter of the circular duct shall prevail, and the length of the outer side of the rectangular duct shall prevail.

The calculation formula for the area of circular duct and rectangular duct is as follows:

Circular duct area S=×πDL

Rectangular duct area S=2L (A+B)

About above:

π —— Pi (3.14159)

—— Outer diameter of circular duct

—— length of duct

——Rectangular duct side length (visible surface on the drawing)

——Rectangular duct side length (invisible surface on the drawing)

The interface form, the thickness of the steel plate and the cross section (perimeter or diameter) of the duct are the three major elements for selecting the quota sub-item. In principle, these three elements must be satisfied at the same time when selecting the quota sub-item.


Section 3 The cutting job of ducts:

    On the market, we can see many kinds of traditional cutting tools, saw, manual blades, etc. These tools are useful and less expensive, but they require huge man power and are time consuming. In the modern HVAC industry, more and more companies and factories have started to use machinery and automation to reduce labor. We can find make kinds of cutting machine on the market too. What you need to find is specifically for cutting ductwork, which will highly increase your efficiency.

For galvanized ducts, you have metal duct  laser cutting machine. For PI ducts, you have PI duct cutter. For thermal insulation cotton, you have insulation cutting machine. All you need will find a solution. We always pursuit high quality and professional work.

We have introduced the basic situation of the production and installation of steel ducts. In actual construction, there are also ducts made of other materials (such as aluminum, stainless steel, and glass steel). The construction methods, acceptance specifications and The selection of quotas all have their own characteristics. We cannot make generalizations, but should pay attention to their corresponding regulations.

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