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Solar Reflectance of High Profile Roofing Materials

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					Solar Reflectance of High
Profile Roofing Materials
An overview of CRRC research and activities


                             Technical Committee Meeting
                             November 17, 2008
                 The Short Story
• Physics shows that profile can decrease the solar
  reflectance of roofing products
• Various studies have attempted to assess the
  significance of the impact and produced
  conflicting results
• The CRRC has established a policy for profiled
  metal roofing products
• The Tile Roofing Institute has conducted their
  own study and is asking the CRRC to establish a
  policy for profiled tile roofing products
                                 Technical Committee Meeting November 2008
           The Physics of Profile
             and Reflectance
• When solar irradience strikes an opaque
  surface, it is either reflected or absorbed
• The angle at which the irradience strikes
  the surface affects the degree of reflection
  and absorption



                              Technical Committee Meeting November 2008
                What is a Profiled
                Roofing Product?
• Proposed definition: A profiled roofing product is
  one that has significant height changes within a
  relatively small area (1 or more inches of height
  change per 1-2 square feet)‫‏‬
• Roofing product profile does not account for the
  profile of the actual roof




                                  Technical Committee Meeting November 2008
            A Shield vs. An Echo
                 Chamber
• For flat roofing materials, reflected solar
  irradience cannot strike again
• For profiled roofing products, some
  reflected irradience beams may intersect
  the roofing surface again, providing
  additional opportunities for absorption


                               Technical Committee Meeting November 2008
                    Tilt Matters

• A flat roofing material presents a uniform
  angle of tilt to the sun's energy
• Profiled roofing materials may present
  many different angles of tilt for a given roof
  structure



                               Technical Committee Meeting November 2008
             How Much Impact?
• Physics dictates that profile will affect solar
  reflectance-the question is, how much?
• Does profile make a significant difference to
  the solar reflectance of roofing products?
• What is a significant difference?
• Are certain products or colors more
  affected?
• Can we quantify and predict the impact?
                               Technical Committee Meeting November 2008
                      Findings:
                        ORNL
• Mr. Desjarlais of ORNL compared stone coated
  metal shingles of two different colors and three
  different form factors (flat, tile, shake).
• Data from this study clearly indicates that as
  profile increases, the solar reflectance of the
  shingle assembly decreases.
• The impact was found to be greater for the light-
  colored samples.

                                 Technical Committee Meeting November 2008
        Findings: CRRC and LBNL
• LBNL and the CRRC conducted a study that
  compared measurements made with E903 and
  E1918
• For all the tile products measured, the average
  solar reflectance of the flat coupon was higher
  than the solar reflectance of the profiled tile
  assembly
• Although the flat coupons used with E903 were of
  the same nominal material, they did not come
  directly from the tiles measured with E1918
                                Technical Committee Meeting November 2008
                    Findings: CMRC
• CMRC compared the flat and profiled solar reflectance of
  three different types of metal roofing product. All tests
  were conducted using E1918.
• For each profile type, measurements were taken for
  three or four different colors.
• All colors and profile types showed some reduction in
  solar reflectance due to profile, but only the Regal White
  standing seam product showed a reduction of more than
  5 points.
• Some of the measurements show an increase in solar
  reflectance for the profiled products. This runs counter to
  the physics underlying the study and introduces the
  question of error in the E1918 test procedure.
                                       Technical Committee Meeting November 2008
        What's Happening Now?

•The CRRC has decided to allow most profiled
metal roofing products to be rated using flat
samples
•TRI is conducting their own study on the impact of
profile on the solar reflectance of tile products
•The CRRC will need to formulate a policy for
profiled tile products so that these items can be
rated

                                 Technical Committee Meeting November 2008
Questions?

				
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posted:7/18/2011
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