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RE: [EnergyPlus_Support] Use of radiant barrier systems in walls/roofs




Bare Galvanized Steel is a selective Absorber !!!
alpha 0.7,  emissivity .LE. 0.1 ......
SEE  CRC Chemistry and Physics handbook ....
ActiveSolar03 ....

--- Scott and Roxanne Munns <munns@xxxxxxxxxxxx>
wrote:
> Agas,
> 
> Thank you for your feedback.  I believe we are also
> considering painting the
> roof white, in addition to a possible radiant
> barrier.  The data I had
> suggested that a white painted roof would still have
> an absorptivity of 0.2,
> which I used in my model.  The aluminum foil in the
> radiant barrier is
> 0.03-0.05.
> 
> I will pass on your comments about how to best paint
> the roof to our project
> manager.
> 
> Thanks again,
> Scott
>   -----Original Message-----
>   From: Agas [mailto:agas@xxxxxxx]
>   Sent: Wednesday, March 16, 2005 9:49 AM
>   To: EnergyPlus_Support@xxxxxxxxxxxxxxx;
> munns@xxxxxxxxxxxx
>   Cc: carl.bauer@xxxxxxx
>   Subject: RE: [EnergyPlus_Support] Use of radiant
> barrier systems in
> walls/roofs
> 
> 
>   Modelling exercises backed up by practical
> experience in Botswana have
> shown that the greatest benefit for least cost
> option to reduce heat gain
> through galvanised steel roof sheets is to paint the
> outside surface white.
> A good quality PVA paint will last quite a few
> years. If you paint the
> sheets after they have been exposed to weather for
> about a year, very little
> preparation is needed. Just wash the roof with
> detergent to remove dust and
> oil. A new galvanised roof will need more expensive
> preparation to get the
> paint to adhere. I have heard that washing with a
> thin cement wash does the
> job quite well.
> 
> 
>   The next best intervention is a ceiling with
> insulation (with a reflective
> upper surface if available), and ventilated roof
> space.
> 
> 
>   Regards,
> 
> 
>   Agas
> 
> 
>   >
>   >
>   > ________________________________
>   >
>   > From: Scott and Roxanne Munns
> [mailto:munns@xxxxxxxxxxxx]
>   > Sent: Tue 3/15/2005 11:36 PM
>   > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
>   > Subject: [EnergyPlus_Support] Use of radiant
> barrier systems in
>   > walls/roofs
>   >
>   >
>   > Hello,
>   >
>   > I am doing analysis on a steel-roofed building
> in Guatemala.  Typical
>   > construction there is just a simple corrugated
> steel roof, with no
>   > other insulation, etc.  Ventilation only, no air
> conditioning.
>   >
>   > I am investigating whether using a radiant
> barrier (aluminum foil
>   > facing on a 4mm thick plastic bubble sheet) is
> appropriate.  Sources
>   > have recommended a 25mm gap between the roof and
> the radiant barrier.
>   >
>   > Can EnergyPlus correctly model the effect of the
> radiant barrier on
>   > the roof heat transfer?  I dug around the
> documentation quite a bit
>   > and couldn't find the answer.  For now, I have
> created a construction
>   > containing: 1.  Steel roof (Material:Regular) 2.
>  Air gap
>   > (Material:Air) 3.  Radiant barrier
> (Material:Regular-R)
>   >
>   > Will radiation cross the air gap, or is the air
> gap just acting as a
>   > thermal resistance (conductivity only)?  If
> there is a better way to
>   > do this, I would appreciate any pointers!
>   >
>   > Thanks,
>   > Scott
> 
> 
> [Non-text portions of this message have been
> removed]
> 
> 


		
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