Re: [EnergyPlus_Support] PTACs behaiving badly

["Michael J. Witte" <mjwitte@xxxxxxxx>]

The problem is coming from interactions between the ZONE SIZING and SYSTEM 
SIZING objects.  The system sizing logic looks at the user specified system 
flow rate and adjusts the zone flow rates that are served by that system so 
that they sum to the same value.  In the eio output file:

   System Sizing, OA, Calculated cooling design air flow rate [m3/s],   6.9477

   System Sizing, OA, User cooling design air flow rate [m3/s],   1.4160    

The ratio of 1.4160/6.9477 = 0.2038

For zone 1E, the ratio of the user flow rate to the calculated flow rate is 

   0.12558 / 0.61616 = 0.2038.

So, this is an effect of trying to autosize portions of two systems serving the 
same zone.

If you change the SYSTEM SIZING for "OA" to as shown below:

    design day,             !- cooling design air flow method
    ,                   !- cooling design air flow rate {m3/s}
    design day,             !- heating design air flow method
    ;                   !- heating design air flow rate {m3/s}

 . . then the PTACs size as you are expecting.

So, it does not appear that you can get both the OA system and the PTACs to 
autosize in the same run.  I will ask the sizing expert, but at this point, I 
can only think of the following approach:

1.  Run the file as you have it - with the OA system sized to a specified flow 
rate.

2.  Take the OA system component sizing results from the eio output and put 
them into the OA system components (leave nothing in the OA system to 
autosize).

3.  Change the SYSTEM SIZING object to be as shown above (or delete it entirely 
- since nothing will be autosizing in that air loop) and re-run.  This run 
should autosize the PTACs as desired.

Mike



On 22 May 2007 at 18:50, asheaffe wrote:

> To all,
> 
> I am still having some trouble getting PTACs to size correctly.  The 
> file that I am working on D1+_404 is posted.  The eio file reports 
> design day flows, but then indicates that the Userdes flows are much 
> lower.  However, I have autosized everything, so as far as I can 
> tell, UserDes should match the design day sizing.  I tried to take 
> the design day flows and hard size them into the idf, inputting the 
> design day flow as the PTAC fan flow, but the eio still reports the 
> faulty UserDes for the PTAC coil.  Then I tried inputting the the 
> design flows directly into the coil objects, but the capacities 
> still size to the faulty UserDes flow.  
> 
> One last note, I have tried every combination of numbers I can think 
> of and still cannot figure out how the UserDes flows were set.
> 
> Any ideas?
> 
> Thanks,
> 
> Andrew
> 
> 
> 
> 
> 
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
> 
> The group web site is:
> http://groups.yahoo.com/group/EnergyPlus_Support/
> 
> Attachments are not allowed -- please post any files to the appropriate folder
> in the Files area of the Support Web Site.
> 
> EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the
> Documentation link and press the "search" button.
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 


========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx





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