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

["Scott and Roxanne Munns" <munns@xxxxxxxxxxxx>]

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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