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  1. #1
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    Air handling Unit sizing

    Can some one guide me on accurate sizing an AHU. 1.5 air changes /hr ? is that right value for an office space? or 8 lit/person?

    thanks

    Kurrodu

  2. #2
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    Quote Originally Posted by kurrodu View Post
    Can some one guide me on accurate sizing an AHU. 1.5 air changes /hr ? is that right value for an office space? or 8 lit/person?

    thanks

    Kurrodu
    If you're looking for "accurate sizing", throw out any rules of thumb (i.e. air changes, CFM/SF, SF/ton...etc).

    You have to start perform heating & cooling load calculations for the space/building. And unless you're a very quick learner, forget about trying to do this cold! If you're a contractor, team up with a seasoned HVAC consulting engineer.

  3. #3
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    AHU Sizing

    I did the heat loads using design builder for a 1000 sqmt office space divided into 4 equal zones.

    It has a cooling load of 100 W/sqmt

    So I plan on using 40 TR Chiller. I think I need to use 1 AHU for each zone making it 4 AHU units

    So how do I go about sizing the AHU now

  4. #4
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    you can't be serious can you?

    I ain't going to provide any info - pay mech engineer to do the proper design and load calcs for a 11,000 sqft space

    what if It doesn't work what if the loads you calculated are wrong what if this is in florida or some where else thats closr to the equator
    based upon you working in metric I'd say this is likely to be other than north america.

    I'll say this right now the cubic air per minute standard in North America per ton of cooling capacity is cubic feet per minute

    This may not apply to the equipment available to you

    Also I did a basic calc based upon the sq ft you stated and I think you are off a bit - so much is going to depend upon where the building actually is - the glass size and amount - the internal staff/equipment load

    A chiller/ahu combination is something that needs correct calculations and some one whom knows what they are doing locally - get it wrong and you are up the creek
    www.vetopropac.com - The best tool bags on the market - The offical tool bag of choice by techs everywhere

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  5. #5
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    get the design specs for the ahus you have chosen and get an engineer to assist wit hthe project
    www.vetopropac.com - The best tool bags on the market - The offical tool bag of choice by techs everywhere

    Arguing with some people is like wrestling a pig - eventually you realise the pig actually enjoys it

    Gonads serve a useful purpose but are no substitute for brains

  6. #6
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    Thank you

    Quote Originally Posted by The Penguin View Post
    get the design specs for the ahus you have chosen and get an engineer to assist wit hthe project
    Hey thanks for the feedback. I am a mech engineer my self learning just graduated from ASU. I am doing this project on paper trying to learn. In reality this is not a project that I am going to execute.

    Thank you

  7. #7
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    Quote Originally Posted by kurrodu View Post
    I did the heat loads using design builder for a 1000 sqmt office space divided into 4 equal zones.

    It has a cooling load of 100 W/sqmt

    So I plan on using 40 TR Chiller. I think I need to use 1 AHU for each zone making it 4 AHU units

    So how do I go about sizing the AHU now


    you need to lay out the ducting and load -assuming its equal loads per ahu you need ahus capable of 40tons cooling in total based upon your selection of 40 ton chiller capacity
    Don't forget a margin error +/- % - its damm hard to get more outa a ahu or a chiller than its to get less.

    If you are an engineer you should be able to buy a text book covering this kind of thing and understand it
    www.vetopropac.com - The best tool bags on the market - The offical tool bag of choice by techs everywhere

    Arguing with some people is like wrestling a pig - eventually you realise the pig actually enjoys it

    Gonads serve a useful purpose but are no substitute for brains

  8. #8
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    Cool

    Quote Originally Posted by kurrodu View Post
    I did the heat loads using design builder for a 1000 sqmt office space divided into 4 equal zones.

    It has a cooling load of 100 W/sqmt

    So I plan on using 40 TR Chiller.
    I think I need to use 1 AHU for each zone making it 4 AHU units

    So how do I go about sizing the AHU now

    100 * 1000 = 100,000 W = 341,300 BTUh = 28 Tons
    30 Ton chiller is needed, NOT 40.

    28 Ton /4 AHU = 7 TR / AHU
    or as specifically stated in the Load Calc for each zone.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  9. #9
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    Question O.A. Requirements

    Quote Originally Posted by kurrodu View Post
    Can some one guide me on accurate sizing an AHU. 1.5 air changes /hr ? is that right value for an office space? or 8 lit/person?
    What does the Mechanical Code for Your state require?

    Most U.S. state codes have adopted ASHRAE 62.1.
    Your state or country could use something else.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  10. #10
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    Quote Originally Posted by dan sw fl View Post
    What does the Mechanical Code for Your state require?

    Most U.S. state codes have adopted ASHRAE 62.1.
    Your state or country could use something else.
    I gurranty you he is in another country
    - I'm reluctant to provide more than general info as I fear he is sizing a real job

    also bear in mind his load pr sq metre may not atke into account infiltration so he may need that full 40 tons and then some if the job is close to the equator or other hot places
    www.vetopropac.com - The best tool bags on the market - The offical tool bag of choice by techs everywhere

    Arguing with some people is like wrestling a pig - eventually you realise the pig actually enjoys it

    Gonads serve a useful purpose but are no substitute for brains

  11. #11
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    Quote Originally Posted by kurrodu View Post
    I am a mech engineer my self learning (?) just graduated from A.S.U.
    What does A.S.U. stand for ?

    Why did you not register as a professional member on this site?

    Also, please complete contact info and group associations in your profile!
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  12. #12
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    A.C.H. : Air Change per Hour

    Quote Originally Posted by The Penguin View Post
    ... may not take into account infiltration so he may need that full 40 tons and then some
    O.A. was initially defined as 1.5 A.C.H.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  13. #13
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    Dan,

    I am new to this HVAC-Talk forum. I will register as a professional member soon and A.S.U stands for Arizona State University.

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