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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. Originally Posted by kurrodu
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.

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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. 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

5. get the design specs for the ahus you have chosen and get an engineer to assist wit hthe project

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Thank you

Originally Posted by The Penguin
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. Originally Posted by kurrodu
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

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Originally Posted by kurrodu
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.

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O.A. Requirements

Originally Posted by kurrodu
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.

10. Originally Posted by dan sw fl
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

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Originally Posted by kurrodu
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?

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A.C.H. : Air Change per Hour

Originally Posted by The Penguin
... 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.

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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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