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Re: [EnergyPlus_Support] Supply fan and Return Fan Air Flow Rate



You are correct, ZONE EXHAUST FAN is a constant volume fan.  The flow rate can 
be scheduled, but it cannot track the system supply volume in a variable volume 
system.

A relief air fan will not accomplish what you want.  For a variable volume 
system, there is no way to reduce the central exhaust flow by a percentage of 
total system flow.  You will need to let the return fan have the same flow rate 
at the supply (non-pressurized system).  By adjusting the return fan power and 
the effectiveness of the heat recovery unit, you can make the simulation behave 
as if there was 10% less return air flow.

Mike


On 6 Nov 2006 at 14:55, Zhen Tian wrote:

> Thank you very much for your response, Mike.
>    
>   I guess the zone exhuast fan is the constant air flow fan module, right?
>    
>   If both supply and return fans are variable air flow fans, then the zone
> exhaust fan cannot be used. Can I use fan: simple:variable volume as the
> relief fans with delta presssure as zero?
>    
>   Thanks again.
>    
>   Regards,
>    
>   Zhen
>    
>   
> "Michael J. Witte" <mjwitte@xxxxxxxx> wrote:
>           EnergyPlus currently requires that all flow rates in an air loop be
> balanced. 
> To model a system like this, you must specify zone exhaust fans which remove
> 10% of the flow directly from the zones. Set the ZONE EXHAUST FAN delta 
> pressure to zero so that it does not consume additional electric power.
> 
> Mike
> 
> On 3 Nov 2006 at 11:43, Zhen Tian wrote:
> 
> > Dear All,
> > 
> > I experienced a problem when I modelled supply constant volume fan and
> > return fan in the same air system. The air system uses 100% outdoor air
> flow
> > with heat recovery. The supply fan air flow rate is 0.62m3/s. When I did
> not
> > add the return fan, the system node check shows the system air flow rate
> is
> > 0.62m3/s. To represnt the real situation, a return fan was added to the
> air
> > system with the fan air flow rate of 0.56m3/s (90% of supply flow rate so
> that
> > room has 10% positive pressure). However, I found that the system supply
> air
> > flow rate was also reduced to 0.56m3/s. When I change the return fan
> airflow
> > rate, the system supply air flow rate always keeps the same as the return
> fan
> > airflow rate.
> > 
> > In my air system, the component configuration sequencey is "return
> > fan-cooling coil-heating coil-supply fan". The heat recovery unit is also
> in
> > the air system but not listed in the air system branch. Could somebody
> help
> > me out of this problem? I have no ideal what is wrong with the
> configuration.
> > I cannot find an example that includes both return fan and heat recovery
> unit
> > in the air system.
> > 
> > Thanks a lot for your help in advance.
> > 
> > Regards,
> > 
> > Zhen
> > 
> > 
> > 
> > ---------------------------------
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> > 
> > 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
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> > 
> > 
> > 
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> 
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support 
> EnergyPlus-Support@xxxxxxxx
> 
> 
> 
>          
> 
>  
> ---------------------------------
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> 
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> 
> 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
> 
> 
> 
> 
> 
> 


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





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