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