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  1. #1

    Exclamation Exhaust fan capacity for generator

    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?

  2. #2
    Join Date
    Jun 2003
    Location
    Chicago, IL
    Posts
    4,490
    Are you talking about the combustion exhaust (smoke) or heat exhaust (from the radiator)

    The combustion exhaust should not have any fans. It should be a sealed, insulated piping system the goes straight to the outdoors.

  3. #3
    Quote Originally Posted by craig1 View Post
    Are you talking about the combustion exhaust (smoke) or heat exhaust (from the radiator)

    The combustion exhaust should not have any fans. It should be a sealed, insulated piping system the goes straight to the outdoors.
    Thanx a lot mr.craig for your valuable time and response.
    You caught it ryt. Its combustion exhaust. As i am from construction field and so doesnt have much knowledge about this subject.
    Can you please give me some details about what shall be done. And how it has to be carried out. I mean, is the duct/pipe size that was selected is ok to carry away the air.
    And we will be running a straight duct of GI sheet above false ceiling through which the droplets will be connected to the outlet of the generator.
    Turbo exhaust temp of generator is specified to be 550C. Do we have to use a fire rated duct for the process or the temp will fall down more until it reach outlet?
    Should i remove the fan and just directly run the duct outside the room into the atmosphere?
    Please help as this issue shall be resolved soon.
    Thanx for your concern again !!

  4. #4
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,051
    Sounds dangerous.

    Is this generator room or attic space anyway joined with occupied areas?

    The sheer temp is way higher than we deal with typically. Ive seen exhaust glow red before. And you mention its turbo diesel?

  5. #5
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,051
    A fan wont live lng in that app.

    Abandon that idea.

    Although you will need some serious air moving to keep coolant from overheat no???

  6. #6
    The temperature mentioned is actually the turbo exhaust temp of diesel generator.
    So i believe that temp might be within the generator during its operation. But the exhaust smoke coming out may not be so hot (my assumption)
    Its just a normal training room with a generator where its operation will be shown to the trainees.

  7. #7
    Join Date
    Sep 2007
    Location
    edmonds wa
    Posts
    251
    I would start with the gen mfr for all the exhaust venting and let them spec it out. They deal with it, puts you out of the loop.If its just venting the room the gen is in they should be able to help out there also. If this is a new job I would write the spec,s into the job, that all this is covered by them,if they want to sell you a gen.

  8. #8
    I was desiring that i can do this on my own with the help of folks on this page.
    And if sent to mnfrer it wil take longer time to get a feedback.
    This was not present during tender stage of project. The project is almost finished and during handing over the client requested for this. So, u may understand the rest..!

  9. #9
    I wish mr.craig come up with a solution for my query !!

  10. #10
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by craig1 View Post
    Are you talking about the combustion exhaust (smoke) or heat exhaust (from the radiator)

    The combustion exhaust should not have any fans. It should be a sealed, insulated piping system the goes straight to the outdoors.
    +1 anytime I've seen this done its vented outdoors directly. Unless its a really long run, you should be able to size a flexible ss pipe designed for this application.

    This can basically be treated the same add a oil boiler....except ours a positive displacement pump so you need a heavier duct/pipe. A diesel vs. tolerate some backpressure. Its common to use those small flappers on to of the stacks to keep rain out.

    Sent from my DROID RAZR using Tapatalk 2

  11. #11
    Quote Originally Posted by motoguy128 View Post
    +1 anytime I've seen this done its vented outdoors directly. Unless its a really long run, you should be able to size a flexible ss pipe designed for this application.

    This can basically be treated the same add a oil boiler....except ours a positive displacement pump so you need a heavier duct/pipe. A diesel vs. tolerate some backpressure. Its common to use those small flappers on to of the stacks to keep rain out.

    Sent from my DROID RAZR using Tapatalk 2
    Ya its not a long run. Maximum 13m of run. So do you think the fan is not necessary to be installed?
    What about the selection of duct material etc?

  12. #12
    Join Date
    Sep 2007
    Location
    edmonds wa
    Posts
    251
    The mfg should have all this info in the install doc,s or be able to provide on short notice.There is a lot of knowledge on this site but asking to design a fix for this problem,this late in the job, should be on the people who sold and installed said gen. Or maybe do not buy the same brand again.

  13. #13
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,413
    Hmmm...

    About 13 meters (around 40 ft US) is a fair run for a flue (what we call an exhaust pipe from a stationary fuel burning appliance). Flue engineering is VERY complicated... more going on than meets the common thought process.

    I would definitely contact the manufacturer on this... and while you are at it; do you have enough MUA; that is 'make up air'? MUA is the air which MUST come in to displace the exhaust going out. This is a zero sum game, if you do not have enough air coming in... well your diesel generator will choke and quit. Another thing to verify with the manufacturer is BTU's of heat you need to exhaust to cool the engine.

    I am not being difficult; just trying to get you to realize you are asking for trouble if you do not think out these things and find solutions that work.

    Good luck!
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

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