Sizing Ratio

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Hi all,

Can anyone help me with this two question?

As I model a high-rise building using"Floor Muliplier", I have a floor
(middle) which actually represent the load for 17 floors.

Now I want to link this floor(s) to a certain HVAC system.

Can I simply put "17" in System Sizing > Sizing Ratio ?

Thank you in advance !


Kim, DongEun(DE) 

DongEun Kim's picture
Joined: 2011-09-30
Reputation: 0

If the 17 floors have a collective design cooling load of 100 tons, then
you'll end up with a system capacity of 1,700 tons by doing that to the
sizing ratio... I don't think that's your intent!

If you wish for your heating/cooling capacities to be auto-sized with
some "fluff" to account for extreme heating/cooling conditions and
internal loads that your TMY-based model might not reflect, then by all
means give your auto-sized capacities a sizing factor higher than 1.

If the modeled loads are 1/17 of what they should be in the end, I think
you would need to address the loads directly before trying to adjust the



Nick-Caton's picture
Joined: 2011-09-30
Reputation: 805

You will find that your floor multiplier (& space multiplier if it is
used) are carried over as zone multipliers. So, the values you put in
at the zonal level will be multiplied by your floor multiplier. The
values you put in at the system level will be for the overall system
serving all 17 floors -- if capacities are not entered then the overall
capacity based on the auto-sizing will be used. You do not need to put
"17" in for the sizing ratio.

bfountain's picture
Joined: 2011-09-30
Reputation: 201

Thank you Ncik and Brian !

Let me rephrase my question.
The building has one AHU per floor,
I thought I could put the coil capacity, fan cfm (not auto-sizing), and
everything as they are designed then just expand the capacity with sizing
ratio to fit
the expanded load by floor multiplier.
Does it make sense?

And one more thing,
when there are more than one FCUs for a zone, could I just model one FCU and
apply the number of FCU in sizing ratio?

Many thanks in advance.


2011/6/28 Brian Fountain

DongEun Kim's picture
Joined: 2011-09-30
Reputation: 0