ventilation and fan selections

[kathir]

dear all...

please guide me to select a fan for a ventilation system.ie. fan selection,static pressure,rpm,cfm calcuations...etc

regards/kathir

[Brian_UK]

As a wise gentleman from your country stated some years ago....

For designing an Air Handling Unit, you should first have to design the Coil size. The next thing is to select the proper fan. If you are proposing to manufacture AHU then you got to have a knowledge on the same. Otherwise there are a lot many AHU manufacturers in our country. You can get a lot of good informations from the web site shown below.

http://www.swegon.com/

Click on resources.

[Sridhar1312]

what is the application? It depneds on the load or heat to be removed or air changes required then only the fan selection will come.
Standard way is to arrive at the air quantity and the components like Fan transformation, filter, intake lovers, cooling coil, ducting registers etc which come in air distribution circuit.
Every companent will have resistance against the air quantity which are summed up to get the total static required.

[ahmed eltaweel]

brain_uk sir
i'm pleased to know you sir

[Brian_UK]

Originally Posted by ahmed eltaweel

brain_uk sir
i'm pleased to know you sir

And you also Ahmed,

[B G Scott]

Originally Posted by kathir

dear all...

please guide me to select a fan for a ventilation system.ie. fan selection,static pressure,rpm,cfm calcuations...etc

regards/kathir

I don't know if the best book on air side design is still in print but do try and locate a copy of "WOODS practical guide to fan engineering", it will not matter if it is OLD fan laws do not change.
The definition of a fan is a "machine which propels air continuously by aerodynamic action"
There are three basic types of fans, centrifugal, propeller and axial.
All three are selected for different types of applications the major selection criteria being external resistance, noise etc.
Fan Laws.
With constant impeller size
1. Volume flow varies directly as speed of rotation
2. Pressure developed varies as (speed of rotation)2
3. bhp absorbed varies as (speed of rotation)3

With constant speed of rotation
4. Volume flow varies a (impeller size)3
5. Pressure developed varies as (impeller size)2
6. bhp absorbed varies as (impeller size)5

Consequently with varying speed of rotation and impeller size
7. Volume flow varies as (speed of rotation) x (impeller size)3
8. Pressure developed varies as (speed of rotation)2 x (impeller size)2
9. bhp absorbed varies as (speed of rotation)2 x (impeller size)5

I am sorry that the system does not allow the (squared 2) or the (cubed 3) etc. to be put in the correct location ie against the bracket above the base line.

To answer your original question, first you have to determine the air volume required to ventilate the space under consideration. The next phase of selection requires a calculation of the air distribution system, ductwork, grilles, diffusers etc. to provide an assessment of the anticipated external resistance to air flow the fan will have to over come to deliver the calculated air volume.
The type of fan would be selected based on the type of application, for example an axial 2 pole would be acceptable in an industrial application but due to the noise generated a centrifugal would be more appropriate for commercial and residential ventilation systems.

I hope some of this helps.

[kathir]

thanks for the replies..

[Frikkie]

The Woods guide to fan engineering is here for free.

There is also a beautiful noise control book there as well.