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Brad. <br><br>This would be the best for hot climates, and there are many materials that do this. In fact, most materials have a high emissivity, which is a surface property. <br><br>A surface with a low emissivity traps heat, for example for use on a flat plate collector (i.e., high absorptance, low emissivity). <br><br>Jeff
<br>BB 8=! 8=) :=) 8=) ;=) 8=) 8=( 8=) :=') 8=) 8=) 8=? BB
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<br>Jeff S. Haberl, Ph.D., P.E., FASHRAE...................jhaberl@esl.tamu.edu
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<br>Professor......................................................Office Ph: 979-845-6507
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<br>Department of Architecture.......................Lab Ph: 979-845-6065
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<br>Energy Systems Laboratory.......................FAX: 979-862-2457
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<br>Texas A&M University..............................77843-3581
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<br>College Station, Texas, USA.......................URL: www-esl.tamu.edu
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<br>BB 8=/ 8=) :=) 8=) ;=) 8=) 8=() 8=) 8=? 8=) 8=) 8= BB
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<b>From</b>: bldg-sim-bounces@lists.onebuilding.org <bldg-sim-bounces@lists.onebuilding.org>
<br><b>To</b>: bldg-sim@lists.onebuilding.org <bldg-sim@lists.onebuilding.org>
<br><b>Sent</b>: Sun Nov 29 14:57:22 2009<br><b>Subject</b>: [Bldg-sim] Why should roofs have high emissivity?
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It seems to me that a roof that emits more radiation will have a greater warming effect on the building. Some houses in warm climates have radiant barriers because the aluminum has a <i>low</i> emissivity, thus blocking the infrared radiation. But both LEED and Energy Star suggest high emissivity for warm climates. Does this make sense?<br>
<br>From LEED NC Reference Guide v. 2.2:<br><br>"To maximize energy savings and minimize heat island effects, materials must exhibit a high reflectivity and a high emissivity over the life of the product."<br><br>
>From Energy Star website:<br><br>"In warm and sunny climates highly emissive roof products can help
reduce the cooling load on the building by releasing the remaining heat
absorbed from the sun."<br><br>Thanks,<br><br>Brad<br>