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[EnergyPlus_Support] Re: Forcing system behavior
Mike,
Thanks for looking at that.
So, this is news. A "mixture of autosized and user-specified
values...generally does not work well".
Is this even when the EIO file reports correct/acceptable values for
all the autosized parameters?
Just as a comment, the I/O Reference certainly does not lead one to
believe this is the case, the way it is written it seems to encourage
the use of autosizing.
Shaun
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte"
<mjwitte@g...> wrote:
> It is difficult to evaluate what is happening here, because the
file is a
> mixture of autosized and user-specified values. This generally
does not work
> well in EnergyPlus.
>
> The supply air temperature not meeting setpoint appears to be a
problem with
> the cooling coil inputs. Within COIL:WATER:COOLING, the coil
should be allowed
> to completely autosize or be completely specified. Also, there is
more outside
> air flow specified in the outside air controller than in the ZONE
SIZING
> object. Finally, try using COIL:Water:DetailedFlatCooling to see
if that will
> adequately control the supply air temperature.
>
> Mike
>
>
> On 8 Dec 2004, at 2:45, sm278424 wrote:
>
> >
> >
> > Hi Mike,
> >
> > I've uploaded a couple of files (an EPMIDF and an XLS with some
of
> > our results). Your response leaves me puzzled because the zone
> > setpoint is not being met, yet
> > -> unmet demand = 0
> > -> the chilled water coil deltaT at peak is only 2.4C when 5.6C
is
> > design/idf input
> > -> the SA volume is fixed at 73 L/s (more than the bare minimum)
> > -> the SA temperature is too warm because E+ says it has to be
> > warmer (11.67C is idf input)
> > -> the radiant panel flow is not at capacity
> >
> > I wonder if you could see if you see any problems with our IDF
input.
> >
> > About your earlier question, I'm using COIL:Water:Cooling.
> >
> > Shaun
> >
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte"
> > <mjwitte@g...> wrote:
> > > If the unmet demand is zero, then the plant has enough capacity
to
> > meet the
> > > request from the chilled water coil. If the zone setpoint is
still
> > not met,
> > > then the chilled water coil is not delivering enough cooling.
> > Either the
> > > airflow rate is too low, or the supply air temperature is too
> > warm. This could
> > > be a control problem, an airflow sizing problem, or a coil
sizing
> > problem.
> > >
> > > Mike
> > >
> > >
> > > On 4 Dec 2004, at 0:40, sm278424 wrote:
> > >
> > > >
> > > >
> > > > 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...
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > 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
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> > > >
> > > > Yahoo! Groups Links
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> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> >
> >
> >
> >
> >
> >
> > 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
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> > Yahoo! Groups Links
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> >
> >
> >
> >
> >
> >
>
>
>
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support
> EnergyPlus-Support@g...
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