[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [EnergyPlus_Support] DOE-2 and EnergyPlus calculated different cooling loads for the same building
I do not believe any heat transfer is considered between the inner and
outer portions of the light shelf (a Surface:HeatTransfer surface on the
inside, and a Surface:Shading:Attached on the outside). You need to
create two windows, one above the shelf and one below the shelf. See
details under Daylighting Device:Shelf under Group - Daylighting in the
Input/Output Reference documentation. Figure 62 is a bit misleading
since it shows one continuous window from above the shelf to below the
shelf. Figure 63 is a more accurate representation of the two windows
and the two shelf surfaces.
Rob Hitchcock
=======
Simge Andolsun wrote:
> Thank you very much for your reply. Please do not consider my response
> saying that we used purchased air. The uploaded files are the ones to
> be considered.
>
> I have another question related with the modelling of light shelves in
> EnergyPlus. According to the manuals, the part of the lightshelf
> extending towards outside has to be defined as a
> 'Surface:Shading:Attached' object, while the part extending towards
> the interior space is to be defined as a 'Surface:Heat Transfer'
> object. My question is about the crossection these two pieces of the
> light shelf come together. Do they touch each other? If they do, then
> they are actually a single element which will inevitably lead to heat
> conduction from outside to inside. Especially, if the lightshelf is
> metal, the problem will be more serious. If the lightshelf is not not
> actually a single element and it is in fact made up of two
> pieces(outer and inner piece), then how do these two pieces come
> together?...or how do EnergyPlus assume their connection? Is it the
> window itself that stands in between the two parts of the lightshelf
> and prevents conduction?...in other words, is ! the window a
> continuous single window that have one outer and one inner lightshelft
> or are there two windows (upper and lower window) separated by a
> single lightshelf? Could you explain the cross section these four
> objects come together (upper window, lower window, outer shelf, inner
> shelf) in EnergyPlus?
>
> Thanks
> Simge Andolsun
>
> "Michael J. Witte" <mjwitte@xxxxxxxx <mailto:mjwitte%40gard.com>> wrote:
> You say in your response to Edwin that you used Purchased Air, but
> that is not
> the case in the uploaded EnergyPlus input files. These have full-blown
> VAV
> systems. So, it is not clear what is being compared here. Based on a
> quick
> review of the inputs files, there are two obvious factors. One, the
> EnergyPlus
> runs are cooling to 25.56C, while the DOE-2 runs are cooling to 25.1
> to 25.3C.
> EnergyPlus has no throttling range on the thermostat, while DOE-2
> does. Set
> the DOE-2 throttling range as small as possible to achieve closer zone
> temperatures.
>
> The most likely influence which could produce a near-constant offset
> in cooling
> loads is the foundation. In the EnergyPlus simulation, the concrete
> floors are
> exposed to a constant 18C outside surface temperatures. This is not
> realistic.
> If I remember correctly, in DOE-2, the ground temperatures come from the
> weather files, so it's not clear from these files what temperatures
> are driving
> the floors in the DOE-2 model. Looking at the EnergyPlus temperature
> graphs,
> all of the zones are being pulled down to the heating setpoint of
> 21.1C for one
> or more hours at night. The floors are doing this. I suspect the DOE-2
> floors
> have warmer boundary conditions, so that is why the zones do not cool
> down as
> quickly at night. (Also - note that the floor construction in the
> DOE-2 file
> is wrong for Space2-1.)
>
> I would also recommend using custom weighting factors in the DOE-2
> model to
> avoid the need to guess at floor weights.
>
> Mike
>
> On 7 Dec 2007 at 16:59, Simge Andolsun wrote:
>
> > Please find the attached EnergyPlus(1) and DOE-2(2) files. These two
> files are
> > supposed to be the DOE-2 and EnergyPlus simulations of the same
> building. Thus,
> > they are supposed to exhibit the same cooling energy consumptions.
> The cooling
> > energy consumptions, however, differ. Please find the attached line
> graph (3)
> > that shows the cooling energy consumption of the building with
> respect to
> > EnergyPlus and DOE-2 simulations on the peak cooling day (3rd of
> July). The
> > DOE-2 output exhibited twice of EneryPlus results. Please also find
> the attached
> > line graphs (4) that show the temperature fluctuations in the
> interior zones of
> > DOE-2 and EnergyPlus spaces. When compared to EnergyPlus simulation,
> there was a
> > time-lag in the temperature fluctuations of the DOE-2 interior
> space. This made
> > us consider FLOOR-WEIGHT factor in DOE-2 as a probable reason. We tried
> > different floor-weight values. This however did not help much.
> Moreover, the
> > cooling energy graphs (3) showed a very similar
> > behavior although the values were very different. This suggested
> that there
> > might be a single definite reason for the difference in cooling loads
> > calculated by the two programs. With your experience on EnergyPlus,
> which input
> > would you recommend us to check as the probable reason for the
> difference in
> > results?
> >
> > Thanks in advance for your reply,
> > ps: If I should upload the attached files, please let me know.
> >
> > Simge Andolsun
> > Graduate Research Assistant
> > Texas A&M University
> > Energy Systems Laboratory
> >
> >
> > ---------------------------------
> > Never miss a thing. Make Yahoo your homepage.
> >
> > [Non-text portions of this message have been removed]
> >
> >
> >
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov <http://www.energyplus.gov>
> >
> > The group web site is:
> > http://groups.yahoo.com/group/EnergyPlus_Support/
> <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.
> >
> > 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@xxxxxxxx <mailto:EnergyPlus-Support%40gard.com>
>
> ---------------------------------
> Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try
> it now.
>
> [Non-text portions of this message have been removed]
>
>
[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.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/EnergyPlus_Support/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/EnergyPlus_Support/join
(Yahoo! ID required)
<*> To change settings via email:
mailto:EnergyPlus_Support-digest@xxxxxxxxxxxxxxx
mailto:EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx
<*> 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/