Re: [EnergyPlus_Support] Controlling Air Flow rate through HVAC system

[fred buhl <wfbuhl@xxxxxxx>]

Barry and Mike,

Setting the system air flow rate via a schedule was something I wanted 
to do but never got around
to doing. No, the facility for doing it now is not there, but everything 
is set up to implement this.
Generally, the system flow rate is set by the zone terminal units. 
However there is a system level
override in the code. That override is in DataAirLoop in the data arrays 
AirLoopControlInfo
and AirLoopFlow. Specifically, 
AirLoopControlInfo(AirLoopNum)%LoopFlowRateSet is a logical
that if true indicates that the air loop flow rate ise set using 
ReqSupplyFrac. AirLoopFlow(AirLoopNum)%ReqSupplyFrac
is the required flow (as a fraction of DesSupply). The design flow rate 
is available in AirLoopFlow(AirLoopNum)%DesSupply.
You need to write a Set Point Manager that will read a schedule and set 
ReqSupplyFrac and LoopFlowRateSet.
Once you have done that your job is done; the program will automatically 
set the flow to what you have specified.
To write a Set Point Manager go into the SetPointManager module and 
imitate the many examples of managers
that are already there. In particular look for SET POINT MANAGER:WARMEST 
TEMP FLOW which sets
the system flow rate. Note that LoopFlowRateSet is set in the 
InitSetPointManagers subroutine; ReqSupplyFrac
is initialized in the same routine, calculated in the Calc routine, and 
set in UpdateSetPointManagers.

As an alternative you could write a System Availability Manager to set 
the system flow rate, as is done for
night ventilation. But this is more involved; I would go ahead and 
imitate SET POINT MANAGER:WARMEST TEMP FLOW.

Fred Buhl
Michael J. Witte wrote:

>This is not easy.  System airflow is governed primarily by the flow requests of 
>the terminal units.  To accomplish your goal, the easiest approach would 
>probably be to use the DIRECT AIR terminal unit with a VAV supply fan.  DIRECT 
>AIR currently has a fixed flow rate, but I expect it would be rather easy to 
>modify it to allow a schedule multiplier on the flow rate.  If you implement 
>this change, it might be useful to add in to the release version.
>
>Where did you find a schedule for the minimum air flow rate?
>
>Beware of version 1.2.2.  Bugs have been fixed since that was release.  Review 
>the Addressed_Issues-V1-2-3-031.htm list to make sure you are not tripping over 
>any of those issues.
>
>Mike
>
>
>On 15 Jan 2006 at 2:57, zorba2pi wrote:
>
>  
>
>>I am working on IEA Annex #46 at Oklahoma State and we are needing to
>>control the air flow rate through the HVAC system on a schedule.  I am
>>been trying to figure out a way of accomplishing this but so far the
>>only I have been able to find is a schedule to turn the system on and
>>off and a schedule for the minimum air flow rate.
>>
>>I was able to modify the source code to allow the fan power to be
>>calculated off a schedule, but this "back door" approach will not work
>>for everything I need to accomplish?
>>
>>I don't mind doing a simple modification to the source code, but I
>>can't even find where the system flow rate is determined to begin with.
>>
>>Any Ideas?
>>
>>Also, we are using Version 1.2.2 for this case
>>
>>Thank you,
>>Barry Wilson
>>
>>
>>
>>
>>
>>
>>The primary EnergyPlus web site is found at:
>>http://www.energyplus.gov
>>
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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.idf and press the
>>"search" button.
>> 
>>Yahoo! Groups Links
>>
>>
>>
>> 
>>
>>
>>
>>
>>    
>>
>
>
>========================================================
>Michael J. Witte, GARD Analytics, Inc.
>EnergyPlus Testing and Support      
>EnergyPlus-Support@xxxxxxxx
>
>
>
>
>
>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.idf and press the "search" button.
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>  
>


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