[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[EnergyPlus_Support] Re: Forcing system behavior
Thanks Mike,
Can I ask one further question re: zone temperatures and unmet demand.
If the unmet demand is zero, then I should have enough capacity in
the plant loop.
I have a fixed zone cooling setpoint of 23C. But in some of our
simulations we see zone air temperatures that are several degrees
above our setpoint. If the capacity is there, why would my zone air
temp be off the setpoint?
Thanks again,
Shaun Martin
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte"
<mjwitte@g...> wrote:
> 1. If the air loop outlet setpoint is not being met, then the coil
capacity or
> chilled water flow rate or chiller capacity is not adequate. Which
cooling
> coil model are you using? Use COIL:Water:Cooling or
> COIL:Water:DetailedFlatCooling. COIL:Water:SimpleCooling does not
always
> deliver adequate capacity under certain conditions (this model will
not be
> available in the next release).
>
> 2. It is very difficult to get a hybrid forced air/radiant system
to behave as
> desired with current EnergyPlus control options. In your case, if
you want the
> radiant system to modulate, then why use a VAV air system? Perhaps
a constant
> volume system would be better. Also, you should set the air system
to run as
> the first cooling priority, so the radiant system can pick up the
remaining
> load. Alternatively, perhaps the VAV system is oversized? If it
is sized
> smaller so that it cannot meet the entire cooling load, then it
will open to
> full flow, thus supplying a constant volume of air.
>
> 3. With cool surfaces for radiant slabs, it would be expected that
comfort is
> maintained at higher dry bulb temperatures. Check all of the
comfort inputs to
> make sure thay are appropriate (clothing, activity level, air
velocity).
>
> 4. These unmet demands are why #1 is happening. The chiller plant
is not able
> to meet the load, so the chilled water supply temperature rises,
and then the
> coil cannot meet the supply air setpoint. Everything is
simultaneous in
> EnergyPlus, so unmet demands result in unmet setpoints.
>
> 5. Zone/Sys Sensible Heating (and Cooling) do not include radiant
slab system
> loads. (I see we need to clarify the definition of this, or change
the way it
> is reported.) Also, if there is outside air, that will place a
load on the
> cooling coil which is not included in the load delivered to the
zone.
>
> Mike
>
>
> On 1 Dec 2004, at 20:48, sm278424 wrote:
>
> >
> >
> > Hi, again,
> >
> > I'm modeling a single zone with a VAV system and a radiant panel.
I
> > control the mixed air temp, HC water inlet and CC water inlet
with
> > the AIR LOOP OUTLET node, which is controlled by a SETPOINT
MANAGER
> > to a setpoint of 12.2C.
> >
> > What happens at peak cooling load is both the radiant panel and
the
> > VAV box go to full flow, and E+ allows the AIR LOOP OUTLET
> > temperature to modulate.
> >
> >
> > My questions:
> >
> > 1. Is there any way to lock in the AIR LOOP OUTLET temp in order
to
> > allow the supply volume to vary?
> >
> > 2. Can the supply temp and volume both be locked at specific
values,
> > so that the radiant panel modulates more fully? Can you suggest
> > appropriate radiant panel schedules for this?
> >
> > 3. In our models we've seen the FANGER PMV produce PPD values of
> > between 6-10% when zone mean air temperatures are relatively high
eg
> > 77-79F (the PPD formula is from the Engineering doc). Does this
make
> > sense to you? The comfort band seems too wide, in most buildings
> > complaints start flowing whenever zone DB temperatures exceed 75F.
> >
> > 4. When we get UNMET DEMAND on our plant loops in these
simulations,
> > the values are very high, much more than the total zone loads
would
> > ever be. We can't explain the values.
> >
> > 5. With this model the total zone load is the rad panel cooling
rate
> > + the CC rate, but the Zone/Sys Cooling Rate values are all over
the
> > place (but usually quite low). Why should this be?
> >
> >
> >
> > Thanks
> > Shaun Martin
> >
> >
> >
> >
> >
> >
> > 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.
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
>
>
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support
> EnergyPlus-Support@g...
------------------------ Yahoo! Groups Sponsor --------------------~-->
Make a clean sweep of pop-up ads. Yahoo! Companion Toolbar.
Now with Pop-Up Blocker. Get it for free!
http://us.click.yahoo.com/L5YrjA/eSIIAA/yQLSAA/dkFolB/TM
--------------------------------------------------------------------~->
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.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/EnergyPlus_Support/
<*> To unsubscribe from this group, send an email to:
EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/