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[EnergyPlus_Support] Re: Internal mass
I'd like to ask one further question related to this discussion.
Has it been found that the heat balance calculations in E+ produce
significantly different results from DOE2 and Trace with respect to
thermal mass effects?
In the model I'm currently working on the thermal 'lag' seems almost
non-existent.
Thanks
Shaun Martin
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte"
<mjwitte@g...> wrote:
> It is difficult to sort out all of the different heat transfer
mechanisms in a
> particular model. Several issues to explore:
>
> 1. Have you run a case with no partitions and no internal mass to
convince
> yourself that the mass is having an effect. Your various cases as
listed in
> the original posting are all somewhat similar to each other, they
just vary in
> the location and amount of internal mass.
>
> 2. In the file that was posted, if I understand correctly, the
partition walls
> use the contsruction "PartitionAlex" which uses
material "4_1_10001" as the
> outside and inside surface layers. This material has a solar
absorptance of
> 0.25, which is quite low. This will limit how much solar the
interior
> partitions absorb and limit their impact on the space conditions.
>
> 3. The ventilation air does not interact directly with the
partitions/internal
> mass. It only mixes with the zone air, and then the zone air
interacts with
> the zone surfaces. You may notice that internal mass has only a
small effect
> on mean air temperature, but a larger effect on mean radiant
temperature.
>
> 4. How high are the ventilation rates? If they are high, then
the zone air
> temperature will track very closely to the outside drybulb
temperature
> regardless of how much internal mass is present. You might also
try some cases
> with zero ventilation and zero HVAC to see that the internal mass
does indeed
> dampen the temperature swings.
>
> 5. There are limits to how much thermal mass can be effective in
a given
> space. The amount of heat transferred into the internal mass is
limited by
> UAdeltaT for convection and by absorptance*area for radiant and
solar. At some
> point, more mass makes no difference, because there is not enough
heat transfer
> at the surface to utilize it.
>
> 6. The ground temperatures are 16C. This is quite cool and
provides a
> significant heat sink. Decouple the floor from the ground and see
if the model
> behaves more as you would expect. To develop better ground
temperatures, use
> the Slab program described in the Auxiliary Programs document.
>
> 7. Regarding convex zones, the zone must be fully enclosed, and
it must not
> violate the rule about intercepting more than two surfaces. If
these rules are
> violated, the alrogithm does not work properly.
>
> Mike
>
>
>
> On 20 Aug 2004, at 8:42, alexandrevarela2000 wrote:
>
> > Hi Rahul,
> >
> > Thanks for your interest int his matter. You are mainly right.
The
> > internal doesn´t "really" afect loads. But internal mass
> > should "flatten" indoor air temperature curve. and this is not
> > changing that much with increased mass.
> >
> > Partitions interact with outside environment if you use
> > FullInteriorandExterior solar distribution model, since E+
calculates
> > the radiation incident in these interior walls. In this way
> > partitions are affected by outside conditions (sun).
> >
> > This model has natural ventilation. This is another outside
condition
> > affecting internal partitions.
> >
> > I also have a question about convex and non-convex zones. If I
inser
> > partitions in a convex zone, in a way that they don't divide the
> > zone, I can still say that the zone is convex. Is this right?
The
> > thing is that if using the E+ definition of convex ("A formal
> > definition of convex is that any straight line passing through
the
> > zone intercepts at most two surfaces"), the zone is no longer
convex.
> > I hope I could make myself clear...
> >
> > Maybe I will just post a generic model in the files folder so
> > everybody can check out the geometry and fenestration.
> >
> > Thanks alot for your help,
> > Alexandre
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Rahul Chillar
> > <chillarrahul@y...> wrote:
> > > Hello
> > >
> > > As you put it, its lot dependent of building physics.Mainly
because
> > the partitions are not exposed to outside enviornment and its
> > temperature fluctuates with the zones temperatures and the
> > temperature lag depends on its thermal mass.
> > >
> > > Also generally the zones being seperated by Internal
partitions
> > have same temperatures on both the sides of the partitions too.
> > >
> > > Hence the effect of partition is negligible on the loads,
mainly
> > the partition is preventing the convective transfer between the
zones
> > which would have take place had they not been present.
> > >
> > >
> > > Thanks
> > > Rahul Chillar
> > >
> > >
> > >
> > > alexandrevarela2000 <amv@e...> wrote:
> > > Dear all,
> > >
> > > I´ve simulated a building's internal mass like this:
> > >
> > > 1)Internal partitions as InternalMass (construction type
Plywood)
> > > 2)Internal partitions as InternalMass (construction type brick
wall)
> > > 3)Internal partitions modeled as walls (actual surfaces and
not
> > > internal mass) and using solar distribution FullExterior
> > > (construction type brick wall)
> > > 3)Internal partitions modeled as walls (actual surfaces and
not
> > > internal mass) and using solar distribution
FullInteriorAndExterior
> > > (construction type brick wall)
> > >
> > > The results regarding these situations didn´t change that
much,
> > which
> > > doesn´t seem right. On the other hand changing mass properties
for
> > > external walls, roofs or floors does have a large impact on
results
> > > (specially floor mass).
> > >
> > > Could this be E+ software related, or is this relating only to
the
> > > building's physics?
> > >
> > > If you think it helps I will upload the base model.
> > >
> > > Thank you very much,
> > > Alexandre
> > >
> > >
> > >
> > > 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.
> > >
> > >
> > >
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> > >
> > >
> > >
> > > Thanks
> > > Rahul Chillar
> > > Grad Student
> > > Building Systems lab
> > > Univ Of Illinois Urbana Champaign
> > >
> > >
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> >
> >
> >
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> >
> >
>
>
>
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support
> EnergyPlus-Support@g...
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