Ventilation Duct Design

A ventilation duct is one of the most important components of a ventilation system, and its proper functioning is integral to the effectiveness of the entire mechanism. In order to ensure that this particular component functions properly, extreme care must be given to ventilation duct design.

Principles of ventilation duct design

When it comes to ventilation duct design, there are a few basic principles that manufacturers must adhere to, just as others involved in any other type of industrial design would follow. One of the most important things to remember is that as air is coursed through a duct, the action of it rubbing against the side of the duct causes a considerable amount of friction. This of course results in air resistance, which increases with the increasing roughness of the inside surface of the duct. Proper ventilation duct design will therefore take into consideration the smoothness of the duct’s inside surface.

A note on static pressure

This air flow resistance, which is also known as static pressure, actually applies to every part of the ventilation duct design. Experienced ventilation systems designers will therefore make allowances for static pressure in every section of the ventilation system, from the elbows to the branches. Taken all together, this static pressure adds up to what is known in ventilation duct design as back pressure.

Although ventilation duct design that aims to minimize air flow resistance is an important step of the process, it is equally important to choose a fan that is appropriate to the particular system. Some of the most commonly used fans in ventilation duct design are:
Keep in mind that not all fans are the same, and it is interesting to note that a ventilation duct design that employs a family with a simple propeller will provide the most air pressure with the least power requirements. Furthermore, such a fan design will result in virtually zero static pressure.

Conversely, a ventilation duct design that utilizes a centrifugal fan will require a lot more power to produce the same amount of air, and will result in much higher amounts of static pressures as well.

Efficiency in ventilation system design

What all this means is that a ventilation duct design that has high backpressure will be far less efficient than a similar model with low backpressure. You should therefore take this factor into consideration when planning your ventilation duct design.

The duct size will also play a significant role in the effectiveness of a ventilation system. Keep in mind that a larger duct will result in lower static pressure, and smoother duct walls will result in a correspondingly lower static pressure level as well.

The same goes with the design of the duct itself. A straight duct will have much lower static pressure than a similar design with more fittings and transitions. Therefore, it is usually a good idea to go with as simple a ventilation duct design as possible.

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