ID Fan Selection

What is an ID fan?

Induced Draft I believe is what it is!?!?

Are there fans that do not induce a draft???

Hockey fan?

But they indulge in draft

Many sports fans can induce a draft. One of my favorites is Black Butte Porter.

It depends which side of the active component the fan is located.

Fans are usually described as Forced Draft (FD) if they are are upstream of the user or Induced Draft (ID) when downstream. As to whether there is any real difference in the mechanical design of the fans in the two services - I don't think so but that i outwith my experience

If the process is hot, corrosive, or otherwise problematical....

Indeed

My mind has been on Cooling Towers lately and they can have either FD or ID - partly its size, layout, but there isn't such a definitive reason for choosing one or the other.

With a furnace though the combustion air is most commonly FD to avoid fancy materials to cope with the temp and corrosive environment.

However if you were to have an ID fan on the back end of the furnace while it would be expensive based on the exotic materials would the impeller etc be that diffenrent in design.

I feel that it is easier to have a higher head fan if it is FD rather than ID as my gut instinct is that its easier to drive +100mbarg rather than to suck -100mbarg but again this is just an argument of scale.

Too bad there isn't a "great answer" button for me to press! Nice simple graphic to show the problem.

Trade off of expensive alloys for a boiler ID fan is less pressure and stress in the boiler firebox.

So the answer is to use the selection criteria for an FD fan! Why didnt you say so?

Yes, as usual several posters have gone into it more than requested. No doubt the OP should be looking at various aspects, but for motor sizing the main thing needed is the fan absorbed power at duty.

You wish to spin over 3 metric tonnes at 900 RPM?

NO!

This requires qualified mechanical and structural engineers to attempt a safe design of this system. Your question is an admission that you lack any qualification to work on such a system.

Redfred,

Come on..... Let him do it.....

Just make sure you and I are well away from the area.

It would be interesting to see them try picking this fan up.

jitendra...

Lets think about this a bit....

You have not given the massflow rate for the fan (the desired amount of air flow) through the fan) Do you think that this would this affect the motor size ?

How about the media ? Is it air ? Do you think that the air temperature is a factor ?

How about the mechanical connection of the components ? Are they connected by gears, pulleys or couplings ? Each of these has a different parasitic draw on the motor.

Lastly, is this your first involvement with an ID fan ? Is this a re-used fan ?

Direct your question to someone who sells ID fans, not a group of total strangers.

Fans come with motor attached, usually.

What does the fan manufacture recommend? Do you have the installation instructions for the fan? Have you contacted the fan manufacture about the missing documents?

This sure looks like a school homework/ test question

If you have electricity, you could use an electric motor.

If you don't have electricity, you could use an IC engine or some sort of turbine.

That's a heavy fan.

It'll take one of these to turn it.

So he needs a heavy motor. Step one is determining what type of motor and power source.

Nice photo, BTW. Might need to scale the engine size and gearing to drive at 900 RPM.

Nah.

At 14,000 pounds, getting it turning will be the only problem.

I think hand propping will be out of the question.

First obtain the fan performance curves, pressure vs flow and power vs flow. Then work out the system curve, pressure drop varies as flow squared. Plot both on same graph to find duty flow. Get power required from power vs flow curve. Power usually rises with rising flow, so do not overestimate system loss. You might want to select motor for highest point on the power curve.

Usually for a fan starting does not limit motor size, but when you know the power as above you can check acceleration, starting time etc.

You don't. If you've got any sense, you let the fan supplier do it!

This is a MAJOR piece of plant. If this is a new installation either consult the drawings and the consultant that produced them for the answer or, for an existing site requiring a fan motor replacement, consult the drawings or the existing fan motor nameplate and documentation for the answer.

This is not something the purchasing department (for example) should be selecting. Neither is sizing the wiring or protection for said massive fan motor (so don't ask).

Consult the site's consultant(s) or qualified design Engineers (if any) for correct fan motor selection. This will also likely require signoff by either or both parties first before purchase.

If this is a homework question, we don't do those here.

Flow rate is one of the important data required. You can check the fans manufactures technical literatures and get motor details.