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[EnergyPlus_Support] Re: Forcing system behavior
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
> > in the Files area of the Support Web Site.
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >
> >
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