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[EnergyPlus_Support] Re: HVAC modelling - Key definitions
Hi Mike,
I am trying to find a method for modelling chilled water as well. I
was looking into the ice storage item though I am not sure exactly how
this will perform, i.e. resetting the melting point.
Mainly I am worried that:
1. The pumping energy associated with putting the CHW into storage
won't be captured.
2. And more importantly, the discharge rates will be limited by the
'melt' energy and not purely a volumetric flow of CHW at (or close to)
the set point temperature of CHW supply.
Have you been able to verify any models that you have completed using
ice storage with a reset melting point?
Cheers, Alex.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte"
<mjwitte@...> wrote:
>
> Sorry I was reading too quickly about the temperatures.
>
> The hot water storage and solar collectors can be modeled. See
example files
> SolarCollectorFlatPlateWater.idf and WaterHeaterDHWPlantLoop.idf.
These will
> get you started.
>
> For the chilled water loop, the only type of cold storage which is
available is
> ice storage. One approach would be to use THERMAL
STORAGE:ICE:DETAILED with a
> melting point of 7C and revised performance curves. Ice storage
example files
> include 5ZoneDetailedIceStorage.idf,
IceStorage-Series-ChillerDownstream.idf,
> IceStorage-Series-ChillerUpstream.idf and IceStorage-Parallel.idf.
>
> Mike
>
>
> On 9 Jan 2008 at 12:31, anarui.oliveira wrote:
>
> > Thank you.
> >
> > I think I didn't correctly explain the thermal storage item:
> >
> > - The 7/12ºC and 45/40ºC temperatures are the nominal temperatures in
> > the supply and return branches of the chilled and hot water loops,
> > respectively;
> >
> > - The thermal storage tanks are meant to prevent the chiller o boiler
> > to be called to action in less eficient conditions (short on/off
> > cycles, and small thermal loads);
> > - In modelling this, I am assuming that the supply temperature in
> > real conditions may depart slightly from the nominal supply
> > temperatures, and therefore be supplied by the thermal storage tanks,
> > up to certain limits of demand and supply conditions...
> >
> > - Plus, the hot water tank may register temperatures up to 85ºC,
> > thanks to the support of the sollar collectors, through a heat
> > exchanger.
> >
> > With this new description, could any of the systems supported
> > by "Water systems" or "Water heaters" fit to the kind of model I'm
> > trying to implement?
> >
> > If not, would it be posible to implement such a template model in E+
> > (I'd expect it to be a rather standard application in large
> > buildings)?
> >
> > Regards,
> > Ana Rui Oliveira.
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte"
> > <mjwitte@> wrote:
> > >
> > > 1. REPORT VARIABLES are defined in the Input Output Reference
> > document.
> > > Search for the report variable name to locate the definition.
> > >
> > > 2. Yes, the COMPACT HVAC objects which you list are correct for
> > this type of
> > > system (without "reservoirs", thermal storage).
> > >
> > > 3. To change the boiler part load performance, run a simulation
> > with the idf
> > > file containing the COMPACT HVAC objects. Then take the expidf
> > output file and
> > > rename it to <newfilename>.idf. Find the BOILER:SIMPLE object and
> > edit the
> > > part-load coefficients.
> > >
> > > 4. Similar to the boiler, find the CHILLER object in the expanded
> > idf file and
> > > change the part-load performance. If the available inputs are not
> > sufficient
> > > to model the two-stage performance, you may find it necessary to
> > model this as
> > > 2 different chillers, one that represents stage-one operation, and
> > another that
> > > represents stage two?
> > >
> > > 5. If I understand correctly, the boiler controls will turn on the
> > boiler when
> > > the hot water supply tempertaure falls below 40C and turn off the
> > boiler when
> > > the supply temperature reaches 45C? This type of control is not
> > supported. In
> > > the real system, the impact of the reservoirs will be to lengthen
> > the cycle
> > > time of the boiler (or chiller). The only suggestion I have for
> > modeling this
> > > would be to change the part-load curve for the boiler (or chiller)
> > to show
> > > improved efficiency at low loads compared to a system without the
> > reservoirs.
> > >
> > > Mike
> > >
> > >
> > > On 2 Jan 2008 at 8:29, Ana Oliveira wrote:
> > >
> > > > Hi.
> > > >
> > > > I've made a first approach to E+ HVAC models, but I find it
> > difficult to
> > > > correctly interpret all the relevant variables. I don't have much
> > experience
> > > > working with HVAC systems, so I apologize if some of the
> > questions are very
> > > > basic... If that is the case, please tell me so I can refer to
> > more
> > > > general/theoretical docs. I'll try to separate the questions in
> > smaller
> > > > batches!...
> > > >
> > > > I need to model a 4-pipe system for a large service building,
> > served by:
> > > > - a chiller (condenser on the roof) - Operating temperatures:
> > 7º/14ºC;
> > > > - and a set of 3 condensation boilers (fuel: natural gas) -
> > Operating
> > > > temperatures: 45º/40ºC; - with constant flow pumps on the return
> > branches - both
> > > > the chilled and the hot water systems include a reservoir - (plus
> > an auxiliary
> > > > set of vaccum tube solar collectors, that I dropped for now; they
> > will only
> > > > interact through a heat exchanger); - each room as an independent
> > temperature
> > > > control, achieved by a unit that simply recirculates the air
> > (constant flow) in
> > > > the room passing it through the internal heating and cooling
> > coils.
> > > >
> > > > From what I've seen, I think I can properly model the essential
> > of this system
> > > > with the Compact HVAC: - Zone: Fan Coil model, and the respective
> > Thermostat
> > > > (dualband), Hot and Chilled Water Loops (constant flow), Chiller
> > (electric, air
> > > > cooled, constant flow) and Boiler (natural gas, constant flow)...
> > > > ... RIGHT ?... remarks?...
> > > > But:
> > > > - How do I properly model the efficiency of a condensation boiler?
> > > > - How do I model a chiller with a two stage operating compressor
> > (50%-100% of
> > > > maximum power)? - How do I model the thermal reservoirs, at
> > aprox. 7ºC and 45ºC
> > > > (because it will affect the on/off states of the chiller/boiler
> > and thus the
> > > > energetic behaviour of the building, right?....)?
> > > >
> > > >
> > > >
> > ______________________________________________________________________
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> > > > [Non-text portions of this message have been removed]
> > > >
> > > >
> > > >
> > > > The primary EnergyPlus web site is found at:
> > > > http://www.energyplus.gov
> > > >
> > > > The group web site is:
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> > > >
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> > > >
> > > >
> > >
> > >
> > > ========================================================
> > > Michael J. Witte, GARD Analytics, Inc.
> > > EnergyPlus Testing and Support
> > > EnergyPlus-Support@
> > >
> >
> >
> >
> >
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov
> >
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> >
> > Attachments are not allowed -- please post any files to the
appropriate folder
> > in the Files area of the Support Web Site.
> >
> > EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf
under the
> > Documentation link and press the "search" button.
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
>
>
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support
> EnergyPlus-Support@...
>
------------------------------------
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