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RE: [EnergyPlus_Support] Re: Vented PV Cavity

To: <EnergyPlus_Support@xxxxxxxxxxxxxxx>
Subject: RE: [EnergyPlus_Support] Re: Vented PV Cavity
From: "Griffith, Brent" <brent_griffith@xxxxxxxx>
Date: Mon, 24 Jul 2006 10:40:49 -0600
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Thread-topic: [EnergyPlus_Support] Re: Vented PV Cavity

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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