pressure in VFD room

[abeerkhayyat]

I am working on the design of HVAC system for a VFD room, which is a part of a modular building.
My main concern is to apply positive pressure inside the VFD room.
How do I achieve that and what is the recommended positive pressure?


VFD produces 15000cfm hot air.
Room Dimensions are 20’Lx15’Wx14’H
HVAC unit used = 6 tons

Thank you

 

[MintJulep]

Where does the 15,000 cfm come from? Where does it go?

 

[abeerkhayyat]

The 15000cfm is produced from the VFD itself and is blown into the room where the vfd exists.
Thanks

 

[Bribyk]

You're going to have a wind tunnel for a room to keep it cool. Forced draft (fan forcing air into the room) will keep a positive pressure on it. I think 0.25-0.5 inWC is a typical positive room pressure but I'm no HVAC expert. You might want to look for ways to use all this VFD heat.

 

[abeerkhayyat]

Yes, the 15000cfm will be used during winter in heating the VFD room,While during summer it has to be exhausted from the room.It can be also 50% exhausted and 50% blown into the room in certain times.

 

[AbbyNormal]

wow must be a monster drive, sure there is no extra zero or two in there

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

7500 CFM would probably make a F1 votex in that little room

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

let me know if I am just a wise guy with my foot in my mouth on this one, but the airflow sounds pretty high for a room that is only 4200 cubic feet

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[abeerkhayyat]

You are right,let me check this back with the supplier.I guess it has to be 15oo cfm(not 15000cfm)

 

[abeerkhayyat]

Well,I checked the specs. of the VDF --and it produces 15000cfm. I have to explain more ..the room has an external door of 4' x 9' and internal one of 4'x9'.The external temp. is ranging from -2C to 40C. There is another sourse of leakage which is the louvers of the intake fan.
Please tell me what other info might be helpful.

 

[MintJulep]

So the VFD produces air from nothing? That's a neat trick.

Where is the air intake? Where is the air discharge?

With 15,000 cfm to work with in a 4200 cubic foot room you will have no problems establishing a positive pressure - at least until the walls fall down.

 

[abeerkhayyat]

There are air blowers (intake fans) which are blowing external air to the room.
The vfd has a rectifier and a transformer(this is the source of heat).
Exhaust louver to be used to discharge the air outside the room,and an intake grill to be used to recerculate it through the room.

 

[Bribyk]

Then, is your only issue determining, calculating and maintaining a positive pressure?

Since you are blowing air into the room you "should" have a small positive pressure. If you need more you either need a higher pressure fan, smaller outlet louvers or to fix your leaks.

 

[abeerkhayyat]

First,I want to be sure about the recommended positive pressure for such a room?
Is their a formula to calculate?and how to maintain this.
Any other design or control options?

 

[MintJulep]

Generally, the purpose of positive pressure is to prevent dirt from entering the room under doors, and through other leaks in the envelope.

In your case, you are bringing in an AWFUL LOT of outside air via the drive's cooling fans. Every cubic foot of this outside air has some amount of dust in it. Is this outside air filtered? To what degree?

 

[MintJulep]

And take a look at thread403-218830

 

[abeerkhayyat]

The air is filtered through built in filters in the VFD unit

 

[Bribyk]

Why do you need a positive room pressure?

It sounds like your VFD is bringing in filtered air to cool itself and I would bet the VFD is designed to maintain its own positive internal pressure to prevent dust ingress.

 

[delimashare]

At a certain point,during summer time, all the air blown by the intake fans will be exhausted. What is the effect on pressure in this case?

 

[abeerkhayyat]

Now,checking back my A/C unit capacity. Assuming exhausting all the 15000cfm from the VFD to outside.
Do you think 6 ton A/C unit will be good enough to cool the room.