[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [EnergyPlus_Support] Re: Internal mass



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
> > 
> > 
> > ---------------------------------
> > Yahoo! Groups Links
> > 
> >    To visit your group on the web, go to:
> > http://groups.yahoo.com/group/EnergyPlus_Support/
> >   
> >    To unsubscribe from this group, send an email to:
> > EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx
> >   
> >    Your use of Yahoo! Groups is subject to the Yahoo! Terms of 
> Service. 
> > 
> > 
> > 
> > Thanks 
> > Rahul Chillar 
> > Grad Student 
> > Building Systems lab
> > Univ Of Illinois Urbana Champaign
> > 
> > 		
> > ---------------------------------
> > Do you Yahoo!?
> > Yahoo! Mail - 50x more storage than other providers!
> > 
> > [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:
> 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




------------------------ Yahoo! Groups Sponsor --------------------~--> 
Make a clean sweep of pop-up ads. Yahoo! Companion Toolbar.
Now with Pop-Up Blocker. Get it for free!
http://us.click.yahoo.com/L5YrjA/eSIIAA/yQLSAA/dkFolB/TM
--------------------------------------------------------------------~-> 

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

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/EnergyPlus_Support/

<*> To unsubscribe from this group, send an email to:
    EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/