[EnergyPlus_Support] cfm/ton limits file

["asheaffe" <sheaffer@xxxxxxx>]

I examined the issues in Fred's post responding to my question about 
cfm/ton (message and response below) and still cannot figure out why 
my PTACs are sizing the way that they are.  I posted the file for 
more help (D1+_401.idf).  A note about the file - the HVAC systems 
are a bit complicated as I am modeling a DOAS system - so I have one 
system supplying ventilation air to the zones and then PTACs in each 
zone providing secondary heating/cooling.

Thanks,

Andrew







>The air flow is calculated first and is fundamental - it is not 
>altered.
The cooling capacity
is then calculated and is limited by 450 cfm/ton.

The cooling flow rate is basically established by the zone design
sensible cooling load - which is set
by your design day weather, internal loads, outside air requirements,
window & wall heat gains etc.

So, if you are seeing an error by a factor of 6, the questions would 
be:

1) are your design calc inputs correct (does the design flow rate 
seem
reasonable).

2) do you have a huge latent load (from internal sources or outside 
air)?

Upload your file if things continue to ne baffling.

Fred Buhl

asheaffe wrote:
> I am having a problem getting PTAC cooling coils to size correctly.
> The coil cooling capacities are sizing smaller than they should
> (considerably smaller - by a factor of almost 6). The eio file
> reports that the coils are sizing right up at the limit of 450 
cfm/ton
> (6.04E-05 m3/W). Sooo - I am taking this to mean that the low 
tonnage
> is correspondingly limiting the air flow. However, I need more
> tonnage to supply zone temps - so why is the sizing routing 
limiting
> my tonnage?
>
> How do I move them off of this limit? The PTAC air flows are all
> autosized. My zone sizing design cooling temp is 14C - which I 
think
> is fairly resonable.
>
> Thanks for the help,
>
> Andrew
>
>
>
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