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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.
> > > 
> > > 
> > > 
> > > Yahoo! Groups SponsorADVERTISEMENT
> > > 
> > > 
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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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