Exhaust Fan Calculation for a Generator

[mohsinrkhan86]

Hi all,

I work in dubai as HVAC designer. Can anyone please help me in sizing an exhaust fan for a generator with an exhuast of 118 m3/min. However the exhaust gas will have its own velocity to carry itself through the duct, but to avoid any back drop I have decided to provide a fan which wil boost up the flow.

Exhaust outlet of generator is of 200mm dia, & it shall be connected to a duct of 300mm dia as we proposed.

But my query is, how much shall be the capacity of exhaust fan?
I believe it shall not be equal to the exhaust flow (which is too high) but much lesser than it as the fan is just to assist in the gas flow out of the room.

I have roughly selected a fan of 470m3/hr.
Please help me know the flow & esp the fan shall have?

[Brian_UK]

How can you state that the exhaust flow is too high?

If that is the flow from the engine exhaust then it is what it is.

Any extract fan has to create a negative pressure to be able to be effective in it's role.

[mohsinrkhan86]

Ya true. We shall consider the actual exhaust no matter how high it is.
But if we think logically the exhaust itself have some velocity and capable of moving itself out through the duct.
The fan i was planning to install was for some boost to the exgaust as a preventive step against the back drop pressure.
However some people have commented on this page that fan is not required at all. Jus connect the duct to exhaust and it will be carried out.

[knighty]

can you not blow air in instead of sucking it out ?

then you can put the exhaust next to / up to / through the air out duct and forget about it

fan will provide airflow for generator cooling, and exhaust will have no option but to be blown out :-)

[Brian_UK]

You need firstly to find out from the engine manufacturer what is the maximum back pressure allowed in their exhaust calculations so that your duct is sized correctly.

Remember also that the exhaust contains life threatening gases and must be vented safely out of the building.

[mohsinrkhan86]

Thank you all for your valuable time and support. It was a great help