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  1. #1
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    AHU total load calculation?



    Room Size: 168 m3, Air change/Hr: 20, CFM: 1975, Outside Temp:104 F, Room Required temp: 71 F, Outside RH: 85%, Expected RH: 22%, system required 20 % fresh air and 80 % return air.

    So, Sensible Heat: 1.085X1975X(104-71)/12000 = 5.87 Ton
    & Latent Heat: 4.840X1975X (139 - 31.43)/12000 = 86 Ton,

    if I overlook other heating load, then total load = 91.87 Ton, but I don't think so, its too much for 168 m3 room, what was my problem with the calculation? Please help?



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    Re: AHU total load calculation?

    Try electrcal loading from lights, computers, fans, and people loadings. Heat gain from solar effect on windows. heat gain from structure loads, ceilings walls and floors.

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    Re: AHU total load calculation?

    Your problem is that you are probably calculating whole air as fresh air, not mixed!
    You need to handle only 20% of total air flow as fresh air.
    .....................

    Last edited by nike123; 04-05-2011 at 09:53 AM.

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    Re: AHU total load calculation?

    Thanks to you, you always help me lot.

    Can you please provide me the software or the source of the software or how can I calculate it my self?

    Waiting for your kind replay.

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    Re: AHU total load calculation?

    Windows Psychrometrics Calculator 28.00

    http://www.marcobrien.org.uk/

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    Re: AHU total load calculation?

    Quote Originally Posted by nike123 View Post
    Windows Psychrometrics Calculator 28.00

    http://www.marcobrien.org.uk/
    ok I will do it.................
    Last edited by Bashir01219; 04-05-2011 at 12:56 PM.

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    Re: AHU total load calculation?

    Some problem with the calculation......
    1. Supply air dry and wet bulb temperature is not correct our expected temperature 22 Deg C and 22% RH

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    Re: AHU total load calculation?

    That is exactly what I entered as return air.
    Return air is actual state of air in room.
    Supply air is mixing with air alredy in room.

    Check your home air-conditioner suply air and room air.

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    Re: AHU total load calculation?

    But this is not a total summary. Where is my 20% fresh air load and at the starting time room temperature and humidity are same as outside so how can I summaries total scenario?Its a pharmaceuticals plant......
    My point is
    (Room Size: 168 m3, Air change/Hr: 20, CFM: 1975, Outside Temp:104 F, Room Required temp: 71 F, Outside RH: 85%, Expected Room RH: 22%, system required 20 % fresh air and 80 % return air.) if I want to calculate from the beginning what will be the steps?
    1. Sensible Heat: cfmX1.085X (Tout-Tin)/12000 = (0.00 Ton)
    2. Latent Heat: cfmX0.69143X(G1-G2)/12000 = (0.00 Ton)
    Then add lighting, man, machine, sunlight, .........etc load, but problem is at normal condition and initial condition load is not safe so how can I summarized total thing that can help me to predict system total load and buy a AHU.
    Last edited by Bashir01219; 04-05-2011 at 01:35 PM.

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    Re: AHU total load calculation?

    Quote Originally Posted by Bashir01219 View Post
    Where is my 20% fresh air load and at the starting time room temperature and humidity are same as outside so how can I summaries total scenario?Its a pharmaceuticals plant......
    20% fresh air is in the calculation.
    What is not in calculation:
    -Latent load from people
    -Heat gain from the supply air fan
    -Heat gain from the return air fan
    -Heat gain from supply air ductwork portion in unconditioned space
    - Heat gain from return air ductwork in unconditioned space
    - Infiltration (sensible & latent) if any
    - Heat gain from lights
    - Heat gain from plant equipment
    - Heat gain from walls, floors, ceilings and windows
    etc...


    Also, you need to establish what is required time frame to lower your temperature from starting conditions.
    Than , you could calculate aditional cappacity needed for that task.

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    Re: AHU total load calculation?

    In the chart Mixed Air Return, for Supply Air, you take DB:12.3, WB: 11.3, RH:95 why? Is it not what for the room design? RH: 22, Temp.: 22 Deg C.
    Last edited by Bashir01219; 05-05-2011 at 01:39 PM.

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