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[EnergyPlus_Support] Re: Vented PV Cavity
Brent,
Thanks again for your reply.
I have captured the 24-hour outside facade surface temperature,
inside surface temperature and sensible cooling energy.
With ventilated PV, the outside facade surface temperature is
normally lower. However, the sensible cooling energy is higher for
most hours of a day. I think that the reason is that heat gain
accumulation at night is higher because the facade can't contact to
the outside environment. So, little sensible cooling energy can be
reduced until afternoon. Is that right?
I have uploaded the file for observation. You can find 4 sheets in
the excel file "For checking (temp & cooling energy).xls". I have
plottted the outside facade surface temperature and sensible cooling
energy for Aug-8. You can also see the data for Aug-8.
Thanks!
Tony
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Griffith, Brent"
<brent_griffith@...> wrote:
>
> Tony,
>
>
>
> I looked at these files and didn't see a problem.
>
>
>
> For vertical BIPV, you have two options in EnergyPlus. The
first, "Construction with Internal Source" is a more robust model
but it is only for cases where there is no ventilation on the back
side. The second, external cavity model allows modeling the effect
of ventilation on the back side, but experimental research is still
needed to have a better understanding of the model inputs for Cd,
Cv, open area, etc. The Sandia PV model can respond to the module
temperature in both cases, but the changes in efficiency turn out to
be pretty small most of the time. You could model both ways and
compare to see the potential improvements from ventilation.
>
>
>
> Regarding your observation that "resulting annual electricity
consumption is not
> improved," it is difficult to say. I would need to examine
complete input files for both cases (after macro processing
please). Just guessing, I would say the vertical walls are not a
big part of the cooling load compared to the windows, roof, and
internal gains and anything you do to them won't make much
difference. I would compare the two runs by plotting the inside face
surface temperatures for the wall for at least 24 hours.
>
>
>
> Brent
>
>
>
> _____
>
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of lnttony
> Sent: Monday, July 24, 2006 3:45 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: [EnergyPlus_Support] Re: Vented PV Cavity
>
>
>
> Dear Brent,
>
> Thanks for your advices!
>
> I will convert the files for the current E+ version 1.3 after I
> solve my problem.
>
> I have tried using other insulating materials instead of the heavy
> concrete. In addition, I have also tried increasing the height
scale
> for buoyancy, effectiveness for perforations with respect to Wind
> (Cv) and discharge coefficient for openings with respect to
bouyancy
> (Cd). However, the resulting annual electricity consumption is not
> improved. The annual cooling electricity is almost the same as the
> case without vented BIPV. I think attaching the exterior naturally
> vented BIPV can reduce the annual cooling electricity. Besides,
> better PV efficiency can be achieved.
>
> I have uploaded the construction file (exterior wall-> WALL-1) and
> OthersideConditionModel file. I am not sure I set the height scale
> for buoyancy, Cv and Cd correctly. You can also see my exterior
wall
> construction.
>
> Is the "SURFACE:HEATTRANSFER:EXTERIORNATURALVENTEDCAVITY" object
not
> preferable for vertically mounted BIPV?
>
> I am also interested in "CONSTRUCTION WITH INTERNAL SOURCE" for
> PVSpandrlPanel. But, will the efficiency be lower by using this
> model because of higher temperature behind the PV panel?
>
> Thanks.
>
> Tony
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com> , "Griffith, Brent"
> <brent_griffith@> wrote:
> >
> > Tony,
> >
> > I took a look at your files. I didn't succeed at running it
> because it is for E+ version 1.2.2. I would recommend moving to
the
> current E+ version 1.3.
> >
> >
> >
> > It seems that you have set up the PV modeling correctly. The
> basic wall construction here is uninsulated heavy concrete. Adding
> the PV here is increasing the wall's solar absoptivity from 0.7 to
> 0.97 so this could be why the cooling loads go up. This could also
> be one of those non-intuitive situations where adding the first
bit
> of insulation can actually increase cooling loads. Remember that
> the added PV layer will also trap more heat at night and
disconnect
> the underlying surface from cool night sky. You might try adding a
> different insulating layer to test expectations.
> >
> >
> >
> > When using the external cavity model, the Construction should
> describe only the underlying surface and not the air gap and
actual
> outer layer. The models will add these to the outside of the
> Construction. So in your file the walls with PV actually have twp
> layers of glass and air gap. The Material:Air object isn't really
> needed for the SURFACE:HEATTRANSFER: EXTERIORNATURALVENTEDCAVITY
> object (unless you really want double layers of glass and air
> gaps). Your value for the height scale for buoyancy looks like one
> for horizontal orientation, for vertical you might use increase
this
> ¼ or ½ of the PV module height.
> >
> >
> >
> > I hope this helps...
> >
> >
> >
> > Brent
> >
> >
> >
> > _____
> >
> > From: EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com>
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com> ] On Behalf Of lnttony
> > Sent: Monday, July 17, 2006 1:31 AM
> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com>
> > Subject: [EnergyPlus_Support] Re: Vented PV Cavity
> >
> >
> >
> > Dear Brent Griffith,
> >
> > Thanks for your reply!
> >
> > In my case, there is a 3-story building. The west-facing facades
> at
> > the 2nd and 3rd floor were attached with vented PV panels.
> >
> > Files related to the PV panels were uploaded ("For enquiry to
> > EnergyPlus.zip"). There are 3 word document files and the
related
> > items were highlighted in green color. The other files can be
> opened
> > with TextPad.
> >
> > The surface material of the exterior wall is "glass". You can
see
> > the details (highlighted in green color)
in "construction_material
> > (IDF file).doc".
> >
> > If there is any more information I should give you, please ask
me
> to
> > do so.
> >
> > Thanks again.
> >
> > Best Regards,
> > Tony LAM
> >
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com>
> <mailto:EnergyPlus_Support%40yahoogroups.com> , "Griffith, Brent"
> > <brent_griffith@> wrote:
> > >
> > > It is difficult to say with out seeing the file, you could up
> load
> > it.
> > > Did you setup the electric load center and the PV generators
and
> > set
> > > them to be integrated? What is the surface material like in the
> > > reference case?
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > _____
> > >
> > > From: EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com>
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com>
> <mailto:EnergyPlus_Support%40yahoogroups.com> ] On Behalf Of
lnttony
> > > Sent: Friday, July 14, 2006 8:57 PM
> > > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com>
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > Subject: [EnergyPlus_Support] Vented PV Cavity
> > >
> > >
> > >
> > > Dear all,
> > >
> > > I am modeling the building integrated photovolatic (BIPV)
system
> > for
> > > the building facade. The photovoltaic (PV) panels were
attached
> on
> > > the exterior wall with an air cavity between them. I want the
PV
> > > panels to serve as a solar heat barrier. But I have problem in
> the
> > > heat gain on the facade.
> > >
> > > By using "OtherSideConditionsModel", I applied "Vented PV
> Cavity"
> > as
> > > the type of modeling used to determine boundary conditions.
> > > The "SURFACE:HEATTRANSFER:EXTERIORNATURALVENTEDCAVITY" object
is
> > > used to describe the condition. However, there is no heat gain
> > > reduction for the underlying surface (i.e the exterior wall),
> even
> > > the required cooling energy for the corresponding zone is
higher.
> > >
> > > Is there any mistake I have made? Or, is there any part I have
> to
> > > pay attention on?
> > > I would be very happy if I can receive any kind advice and
help.
> > >
> > > Best Regards,
> > > Tony LAM
> > >
> > >
> > >
> > >
> > >
> > > [Non-text portions of this message have been removed]
> > >
> >
> >
> >
> >
> >
> > [Non-text portions of this message have been removed]
> >
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
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