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  1. #1
    Join Date
    May 2011
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    Vietnam
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    Flow calculation

    Hi everybody, this is my first post in this forum. It is nice to learn from you guys about HVAC. My question is for a small application of HVAC.

    When I have to do electrical calculation, the first thing I will think about is the load capacity. But this time I need to do calculation for ventilation of a room (an electrical room). The maximum temperature is about 45degC. The room dimension, as I guess, it covers in 5 meter wide, 10 meters long and 3 meter high. So, we will install a ventilation fan for this room. Yes, this is a requirement.

    So, what is the factor I should think of to do the calculation? What I need to do? What is the method applied for this? If I use an electrical ventilation fan for this room, is that so-call mechanical ventilation? Then what to be called if I use an air conditioner instead?

    Thank you,

  2. #2
    Join Date
    May 2011
    Posts
    33
    He , it is not Flow Cal!!!! ,you must tell more detail about the room where it seat,what kind of Insualation ?what kind of electrical room ? constant produce heat or inpeak time produce heat only ? In HVAC this is cal BTU size cal ,what size of unit to cool down room size?any one give him an idea how to cal the size of AC unit cool down the room !

  3. #3
    Join Date
    Dec 2007
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    houston, texas
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    3,787
    It would depend on what your ventilating it for. How many changes of air you require and how much make up air your capable of bringing back into the room.
    I'm not tolerating Political Correctness anymore, from now on it's tell it like it is.

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  4. #4
    Join Date
    Dec 2010
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    Mooresville
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    lol im just now starting to learn about load calculations at school

  5. #5
    Join Date
    May 2011
    Location
    Vietnam
    Posts
    15
    I am not HVAC expert. My question was clearly for a ventilation mechanism (here is a fan) that will be applied for the room not air conditioning one.

    It means that I need to calculate the fan capacity (how much air flow would be enough) to bring the room temperature from 45degC down to 35degC.

  6. #6
    Join Date
    Jul 2002
    Location
    Yuma, AZ
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    2,361
    Quote Originally Posted by hien.nguyenquoc View Post
    It means that I need to calculate the fan capacity (how much air flow would be enough) to bring the room temperature from 45degC down to 35degC.
    Depends:
    • What is the temperature of the cooling air source?
    • What is the internal heat generated in the electrical room?
    • Is there other heat sources influencing this room? (Sun, people, other)
    • How much time do you have to accomplish this?


    The cooling of each cfm of air will be about .24 BTU per F of temperature difference between the incoming air and the exhaust air.
    You can convert that to metric if you wish. Distribution and circulation of the air within the room will make a big difference on the actual results that you may be seeking.
    "I have never let my schooling interfere with my education."
    Mark Twain
    More at: http://www.quotationspage.com/subjects/education/

  7. #7
    Join Date
    Feb 2011
    Location
    Grand Prairie,TX
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    haha. I like the way lynn put that "Is there other heat sources influencing this room? (Sun, people, other)"

  8. #8
    Join Date
    May 2011
    Location
    Vietnam
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    15
    Dear Lynn,

    If I use a ventilation fan, do I know the cooling air source? Since it will vent the air from the inside out.
    The max temp would be 113degF.
    This is a simple application, so I will not consider those factors.
    I don't understand what you mean by that? Or I will just need to install the the temperature sensor to monitor the temperature then control the fan?

  9. #9
    Join Date
    May 2011
    Location
    Vietnam
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    Dear Lynn,

    If I use a ventilation fan, do I know the cooling air source? Since it will vent the air from the inside out.
    The max temp would be 113degF.
    This is a simple application, so I will not consider those factors.
    I don't understand what you mean by that? Or I will just need to install the temperature sensor to monitor the temperature then control the fan?

  10. #10
    Join Date
    Jul 2002
    Location
    Yuma, AZ
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    2,361
    Quote Originally Posted by hien.nguyenquoc View Post
    Dear Lynn,

    If I use a ventilation fan, do I know the cooling air source? Since it will vent the air from the inside out. Assuming the air replacing the room air is anything less than 113F
    The max temp would be 113degF.
    This is a simple application, so I will not consider those factors. Assuming no heat gain in the room from any sourse whatsoever.
    I don't understand what you mean by that? Or I will just need to install the temperature sensor to monitor the temperature then control the fan? Assuming infinite time.
    The answer is any size fan.

    I know what you want to do but you need to know more about physics before you can even ask the question in a way that it can be answered. In your case the electrical content of the room is adding heat internally. If you have a 10 kw transformer in the room that is 95% efficient, then 5% if the 10 kw is heat (about 1700 BTUh). Wiring, circuit breakers and other electrical components in the room are also adding heat. If you don't know more about the maximum heat entering the room, guess and experiment. That is the old fashioned way.
    I forgot to mention that the replacement air needs a pathway to get into the room and the size of the pathway (or opening) matters also.
    "I have never let my schooling interfere with my education."
    Mark Twain
    More at: http://www.quotationspage.com/subjects/education/

  11. #11
    Join Date
    May 2011
    Location
    Vietnam
    Posts
    15
    Dear Lynn,

    Thank you for opening my eyes especially about the path way. I understand that I should know the total heat.

    But this room is already there. I am sorry not to mention about it the first place. The maximum temperature was taken as less than 113degF.

    We want the temperature should be less than 95degF.

  12. #12
    Join Date
    Jul 2002
    Location
    Yuma, AZ
    Posts
    2,361
    Since you are a student I will suggest that you look at
    http://www.engineeringtoolbox.com/co...ons-d_747.html

    That is as far as I can go unless you had pro status.
    "I have never let my schooling interfere with my education."
    Mark Twain
    More at: http://www.quotationspage.com/subjects/education/

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