Re: [EnergyPlus_Support] Load

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

On 17 Jun 2004, at 14:51, Hannah Yan wrote:

> EnergyPlus's talking about sensible load all the time,
> for example autosizing has no latent load included.
> But in coil setup, there is a outlet air humidity,
> which to me that latent load is also calculated. Does
> this mean that the sizing will be smaller than
> actually needed (total load) in summer design day, and
> therefore a larger sizing factor has to be assigned in
> Miami than in Phoenix?


The sizing routines will take latent loads into account, however, the 
COIL:Water:SimpleCooling model has difficulties at high latent loads.  For best 
results, use COIL:Water:DetailedFlatCooling.  You can let most fields default 
or autosize.

> 
> If I want E+ to calculate latent load energy, is it
> must to have humidity setpoint in the space?
> 

No, that is not necessary.  Sizing of the coil will be based on the mixed air 
conditions using the design day outdoor conditions and the supply air 
temperature and humidity that are specified in the SYSTEM SIZING object.  The 
sizing will be based on the total enthalpy change of the airstream including 
sensible and latent load.

Mike


> Hannah
> 
> --- "Richard J. Liesen" <rliesen@xxxxxxxx> wrote:
> > At 01:52 PM 6/17/2004, Hannah Yan wrote:
> > >What is the difference between Zone/Sys Sensible
> > Load
> > >Predicted and  Zone/Sys Sensible Cooling Rate ( or
> > >heating rate)?
> > 
> > The predicted Load is the load that would be
> > necessary to bring the current 
> > zone conditions to the setpoint.
> > 
> > The Zone/Sys Sensible Cooling Rate is the actual
> > amount of heating or 
> > cooling the system could provide with its given
> > capacities in that time step.
> > 
> > If the predicted is not equal to the corrected than
> > most likely the system 
> > was not large enough, but there are times when due
> > to things like outside 
> > air that it can be larger than predicted.  Whatever
> > is not handled in the 
> > given time step will be addressed in the next time
> > step.  If the system is 
> > not large enough this would show up as a higher
> > temperature in the zone 
> > than the setpoint.
> > 
> > >Why is ZONE1:Zone/Sys Moisture Load Rate
> > >Predicted[kgWater/sec] zero?
> > 
> > This means that there is NO Humidistat assigned for
> > that zone.  Without a 
> > Humidistat there is no setpoint and thus no
> > predicted moisture load.
> > 
> > 
> > Thanks
> > Dr. Richard Liesen
> > Associate Director, Building Systems Laboratory
> > Department of Mechanical and Industrial Engineering
> > University of Illinois at Urbana-Champaign
> > 
> > 
> > 
> 
> 
> 
> 
> 
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========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx



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