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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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