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[EnergyPlus_Support] Re: HVAC modelling - Key definitions
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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> >
> >
> >
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> >
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> >
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>
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support
> EnergyPlus-Support@...
>
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