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Re: [EnergyPlus_Support] Fwd: Re: Cooling set-point not fully achieved

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Fwd: Re: Cooling set-point not fully achieved
From: Richard Raustad <RRaustad@xxxxxxxxxxxx>
Date: Thu, 07 Feb 2008 12:49:21 -0500
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I have looked at this control issue before. I don't think it's the 
mixing objects or other zone loads. And your offset from the set point 
should be pretty small. Not to worry, the overall annual energy use 
should be pretty close. Beside, if you run this building using a 
different building simulation tool, your likely to get a different 
answer. And I believe the difference in these answers will be greater 
than the difference in annual energy use due to the set point offset. If 
it happens all the time, adjust your set point so the "average" zone 
temperature is near your target temperature.

anarui.oliveira wrote:
>
> Could the mixing objects or anything like that contribute to this
> problem? Or some definitions such as humidity ratios or the like?...
> Getting worried here... the aim was exactly to predict the energy
> consumption of a building throughout a year (for official, legal
> purposes)...
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> <mailto:EnergyPlus_Support%40yahoogroups.com>, "anarui.oliveira"
> <anarui.oliveira@...> wrote:
>
> Is this problem equally likely to happen if I use a Purchased Air
> approach?
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> <mailto:EnergyPlus_Support%40yahoogroups.com>, Richard Raustad
> <RRaustad@> wrote:
> >
> > You could try increasing the time step in hour. I have no other
> > suggestions. This is a known issue and we are working to correct it.
> >
> > anarui.oliveira wrote:
> > >
> > > That field is already set to 1, and time step in hours is set to
> 4.
> > >
> > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > <mailto:EnergyPlus_Support%40yahoogroups.com>, Richard Raustad
> > > <RRaustad@> wrote:
> > > >
> > > > What you describe is not a capacity issue, it is related to the
> > > > prediction of loads. If you add the report variable
> for "Zone/Sys
> > > > Sensible Load Predicted" and set the report variable frequency
> to
> > > > detailed, you will see why this is happening. Try reducing the
> > > Minimum
> > > > System Time Step in the System Convergence Limits object. You
> > > probably
> > > > will not eliminate the problem, but it should get better.
> > > >
> > > >
> > > > anarui.oliveira wrote:
> > > > >
> > > > > What if, in a similar (heating) case, water flow doesn't
> reach the
> > > > > maximum when the problem occurs, and increasing the air flow
> > > causes
> > > > > further departure from temperature setpoint?...(Less than
> about
> > > 1.5
> > > > > times the auto-sized air flow also leads to poorer setpoint
> > > > > tracking); reported air flow is always equal to the constant
> > > volume
> > > > > fan flow, and ouside air flow rate is (and must be) user
> > > specified.
> > > > >
> > > > > Regards,
> > > > > Ana.
> > > > >
> > > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > <mailto:EnergyPlus_Support%40yahoogroups.com>, Richard Raustad
> > > > > <RRaustad@> wrote:
> > > > > >
> > > > > > Then try again to manually size the coil in the problem
> zone to
> > > > > twice
> > > > > > the size reported in the eio file. Also increase the air
> flow
> > > rate
> > > > > for
> > > > > > that fan coil unit and fan to twice the autosized value. If
> > > htis is
> > > > > > happening in more than 1 zone, then just pick 1 for now to
> test
> > > > > this out.
> > > > > >
> > > > > > Then tell me what happens to the maximum zone temperature.
> Did
> > > the
> > > > > > maximum zone temperature go down? Also tell me if the water
> flow
> > > > > rate is
> > > > > > at a maximum when the zone temperature exceeds the set
> point.
> > > You
> > > > > can
> > > > > > report "System Node VolFlowRate" for the coil water inlet
> node
> > > and
> > > > > fan
> > > > > > coil air inlet node to easily match volumetric flow rate
> with
> > > your
> > > > > inputs.
> > > > > >
> > > > > > This just sounds like a sizing issue and should be easily
> > > resolved.
> > > > > >
> > > > > > anarui.oliveira wrote:
> > > > > > >
> > > > > > > Apparently, yes, but I set it to autosize (and I think I
> > > already
> > > > > did
> > > > > > > a trial with a larger, user-defined, water flow rate)...
> > > > > > >
> > > > > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > > > <mailto:EnergyPlus_Support%40yahoogroups.com>, Richard
> Raustad
> > > > > > > <RRaustad@> wrote:
> > > > > > > >
> > > > > > > > I have not looked at your input file, can you tell me
> if the
> > > > > water
> > > > > > > mass
> > > > > > > > flow rate through the fan coil is at a maximum when the
> > > cooling
> > > > > set
> > > > > > > > point is not met?
> > > > > > > >
> > > > > > > > anarui.oliveira wrote:
> > > > > > > > >
> > > > > > > > > Please forgive me for insisting, but I DO have some
> > > urgency on
> > > > > > > this
> > > > > > > > > one...
> > > > > > > > > Again, thanks for any help,
> > > > > > > > > Ana.
> > > > > > > > >
> > > > > > > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > > > > > <mailto:EnergyPlus_Support%
> > > > > 40yahoogroups.com>, "anarui.oliveira"
> > > > > > > > > <anarui.oliveira@> wrote:
> > > > > > > > > >
> > > > > > > > > > Hi again.
> > > > > > > > > >
> > > > > > > > > > I'm uploading a new file (Zone36598_cFancoil_exp),
> > > hoping
> > > > > that
> > > > > > > > > someone
> > > > > > > > > > can help me figure out why the cooling setpoints
> are not
> > > > > being
> > > > > > > > > achieved
> > > > > > > > > > for all times when the controls are active (namely
> in
> > > Zone
> > > > > > > 36598).
> > > > > > > > > The
> > > > > > > > > > model consists of Fancoil units created with Compact
> > > HVAC,
> > > > > and
> > > > > > > then
> > > > > > > > > > edited in the expanded file.
> > > > > > > > > > I tried several user-defined and sizing options, but
> > > > > couldn't
> > > > > > > solve
> > > > > > > > > the
> > > > > > > > > > temperature peaks above 25ºC.
> > > > > > > > > >
> > > > > > > > > > Thanks in advance,
> > > > > > > > > > Ana Rui.
> > > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > > > --
> > > > > > > > Richard A. Raustad
> > > > > > > > Senior Research Engineer
> > > > > > > > Florida Solar Energy Center
> > > > > > > > University of Central Florida
> > > > > > > > 1679 Clearlake Road
> > > > > > > > Cocoa, FL 32922-5703
> > > > > > > > Phone: (321) 638-1454
> > > > > > > > Fax: (321) 638-1439 or 1010
> > > > > > > > Visit our web site at: http://www.fsec.ucf.edu 
> <http://www.fsec.ucf.edu>
> > > <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu>>
> > > > > <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu> 
> <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu>>>
> > > > > <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu> 
> <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu>>
> > > <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu> 
> <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu>>>>
> > > > > > > >
> > > > > > > > UCF - From Promise to Prominence: Celebrating 40 Years
> > > > > > > >
> > > > > > >
> > > > > > >
> > > > > >
> > > > > > --
> > > > > > Richard A. Raustad
> > > > > > Senior Research Engineer
> > > > > > Florida Solar Energy Center
> > > > > > University of Central Florida
> > > > > > 1679 Clearlake Road
> > > > > > Cocoa, FL 32922-5703
> > > > > > Phone: (321) 638-1454
> > > > > > Fax: (321) 638-1439 or 1010
> > > > > > Visit our web site at: http://www.fsec.ucf.edu 
> <http://www.fsec.ucf.edu>
> > > <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu>>
> > > <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu> 
> <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu>>>
> > > > > >
> > > > > > UCF - From Promise to Prominence: Celebrating 40 Years
> > > > > >
> > > > >
> > > > >
> > > >
> > > > --
> > > > Richard A. Raustad
> > > > Senior Research Engineer
> > > > Florida Solar Energy Center
> > > > University of Central Florida
> > > > 1679 Clearlake Road
> > > > Cocoa, FL 32922-5703
> > > > Phone: (321) 638-1454
> > > > Fax: (321) 638-1439 or 1010
> > > > Visit our web site at: http://www.fsec.ucf.edu 
> <http://www.fsec.ucf.edu>
> <http://www.fsec.ucf.edu <http://www.fsec.ucf.edu>>
> > > >
> > > > UCF - From Promise to Prominence: Celebrating 40 Years
> > > >
> > >
> > >
> >
> > --
> > Richard A. Raustad
> > Senior Research Engineer
> > Florida Solar Energy Center
> > University of Central Florida
> > 1679 Clearlake Road
> > Cocoa, FL 32922-5703
> > Phone: (321) 638-1454
> > Fax: (321) 638-1439 or 1010
> > Visit our web site at: http://www.fsec.ucf.edu <http://www.fsec.ucf.edu>
> >
> > UCF - From Promise to Prominence: Celebrating 40 Years
> >
>
> --- End forwarded message ---
>
>  

-- 
Richard A. Raustad
Senior Research Engineer
Florida Solar Energy Center
University of Central Florida
1679 Clearlake Road
Cocoa, FL  32922-5703
Phone:   (321) 638-1454
Fax:     (321) 638-1439 or 1010
Visit our web site at: http://www.fsec.ucf.edu

UCF - From Promise to Prominence: Celebrating 40 Years



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