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Re: [EnergyPlus_Support] Re: I add a window, but the temperature inside the building doen't change
On 10 Oct 2007 at 5:39, Daniel Solís wrote:
> How do I decouple the floor from the ground?
By setting the outside face environment of the floor slab to OtherZoneSurface,
and setting the outside face environment to be itself. Search for adiabatic in
the Input Output Reference. Or another option would be to set the floor to see
Exterior Environment instead of ground - just to illustrate what is driving
this model.
>
> Physically, would it make sense to decouple them? (I ask because in
> the documentation says the temperatures obtained by the Slab and
> Ground Temperature Programs are so that E+ already partially
> decouples the ground and the slab, so that it fixes some problems).
>
Pysically it does not make sense. I suggested this so that you could see the
effects of the exterior environment on the unconditioned space without the
impact of the floor heat transfer. The Slab progams takes the user inputs for
average monthly indoor air temperature and run multiple years until the ground
field temperatures converge (stop changing). If the whole building simulation
shows the zone temperature to be significantly different from the original
inputs to the Slab program, then new average indoor temperature must be input
and Slab re-run. For unconditioned spaces, this becomes an iterative process
which may take several rounds to get a valid model.
> I still don't get one thing. You say the temperature inside the
> shoebox doesn't change because the ground temperatures under the slab
> are characteristic of a conditioned space, so they drive the
> simulation and the window has a U-value similar to the one in walls.
>
> But, most of the energy (in the day) entering the shoebox through the
> window is via radiation, not convection.
>
> And, the ground 'conditions' the room so quickly that the radiation
> entering through the window has no time to change the inside
> temperature?
It is not a matter of time, it is a matter of balancing heat flows. I ran this
building in Chicago, IL, USA (could not tell from the input what the intended
location is), and reported "Zone Window Heat Gain" and "Zone Window Heat Loss".
The peak gain from the window is only 720W. The walls and floor of this
shoebox have no insulation, so 720W is going to do little to change the
conditions inside the zone. Use REPORT, SURFACES, DETAILS; to report the
nominal u-values and areas of the surfaces. I think you will find that the
heat flows through the opaque walls are much greater that the impact of the
window - with or without the floor issue.
Mike
>
>
> Thanks
>
> Daniel
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte"
> <mjwitte@...> wrote:
> >
> > The shoebox is unconditioned, but the ground temperatures under the
> slab are 17-
> > 21C which is representative of a conditioned space. So, the ground
> > temperatures are driving the entire simulation for this model. The
> window is
> > small and it has similar thermal properties to the exterior walls
> (window u-
> > value=6, wall u-value=4). To see the impact you expect, either
> change the
> > ground temperatures, or decouple the floor from the ground.
> >
> > Mike
> >
> >
> > On 2 Oct 2007 at 19:45, Daniel Solís wrote:
> >
> > > I'm newbie in e+, so I started simulating a shoebox-shaped room.
> Then,
> > > I added a window (single 6mm clear glass, 1m2) facing to the
> south.
> > > When I compare the temperature in the inside with and w/o the
> window,
> > > it's almost the same (few hundreths of difference), which doesn't
> make
> > > sense.
> > >
> > > I uploaded the file, it's Odon3.idf
> > >
> > >
> > > Thanks
> > >
> > > Daniel Solís
> > >
> > >
> > >
> > >
> > >
> > > The primary EnergyPlus web site is found at:
> > > http://www.energyplus.gov
> > >
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> > >
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> under the
> > > Documentation link and press the "search" button.
> > >
> > > Yahoo! Groups Links
> > >
> > >
> > >
> > >
> > >
> >
> >
> > ========================================================
> > Michael J. Witte, GARD Analytics, Inc.
> > EnergyPlus Testing and Support
> > EnergyPlus-Support@...
> >
>
>
>
>
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>
>
>
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