Re: [EnergyPlus_Support] Fixed Minimum outside air rate

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

On 10 Oct 2007 at 18:28, aboyemeplus wrote:

> I am running sizing simulations using winter and summer design-day 
> weather data. The minimum ventilation rate is set to a fixed value. 
> All other plant/system/zone level flow rates are auto sized. 
> While the results show the correct O/A rate for the summer design 
> day, winter O/A flow rates are much lower than the minimum fixed 
> rates entered in Zone/System sizing objects. 

In CONTROLLER:OUTSIDE AIR, the MinimumLimit field is set to "PROPORTIONAL 
MINIMUM".  This means the outside air amount will vary in proportion to the 
total system air flow in this VAV system.  If you want the OA quantity to 
remain constant as the system flow varies, set this field to "FIXED MINIMUM".

> The results also show that peak system heating and cooling capacities
> are comparable to values generated using a simpler model, one with
> "PURCHASED AIR" objects. However, the subject model depicts
> simultaneous heating and cooling during both design days, resulting in
> zone temperatures not meeting setpoint.  Can anyone help me figure out
> 1)Why the minimum fixed outside rate is not applied to winter design
> calculations, and 2)Why there is simultaneous heating and cooling
> during design day calculations. 

There is simultaneous heating a cooling because the chilled water coil leaving 
air setpoint temperature is 12.78C and the heating coil air setpoint 
temperature is 37.8C.  The coil controls on this system use SET POINT 
MANAGER:SCHEDULED, so they have no sensitivity to zone loads.  

Also, the VAV terminal units "SINGLE DUCT:VAV:NOREHEAT" will not vary air flow 
rate when there is a heating load in the zone, they will stay at minimum flow.  

What type of system are you trying to model?  How is it controlled?

Mike


> 
> I have uploaded the Input file in the Problem Submittals\MAB3 folder.
> 
> Thank you for your support.
> 
> Merid 
> 
> 
> 
> 
> The primary EnergyPlus web site is found at:
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> 
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> 
> Attachments are not allowed -- please post any files to the appropriate folder
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> 
> 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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