{"id":3331,"date":"2015-11-06T08:00:11","date_gmt":"2015-11-06T14:00:11","guid":{"rendered":"https:\/\/www.ulprospector.com\/knowledge\/?p=3331"},"modified":"2018-07-11T13:16:56","modified_gmt":"2018-07-11T19:16:56","slug":"pc-beat-the-heat-with-solar-reflective-coatings","status":"publish","type":"post","link":"https:\/\/ulprospector.ul.com\/3331\/pc-beat-the-heat-with-solar-reflective-coatings\/","title":{"rendered":"Beat the Heat with Solar Reflective Coatings"},"content":{"rendered":"

\"Figure1SolarReflective\"According to EPA statistics, approximately $40 billion is spent annually in the U.S. to air-condition buildings. The incorporation of solar reflective pigments<\/em> in paint can decrease the cost to air condition buildings in the U.S. by more than\u00a0$8 billion.<\/p>\n

When exposed to sunlight, it is commonly known that light colors, especially white, remain cooler than darker surfaces. Darker colors, especially black, absorb infrared light energy, resulting in warming of the substrate. The amount of light energy\u00a0absorbed is dependent on color.<\/p>\n

Other factors that determine an\u00a0object’s temperature in an outside environment, in addition to it\u2019s color and solar reflectivity,<\/em> include it\u2019s emissivity, convection and conduction. To illustrate further, Figure 1 indicates at an ambient air temperature of 20\u00b0 C, a white object will remain at about 20\u00b0C, whereas a black object will be about 35\u00b0 C for the coating surface of a steel building.<\/p>\n

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However this same black coating will have a surface temperature of about 65\u00b0C if the coated substrate is wood, plastic or isolated steel sheets. Key definitions follow:<\/p>\n

Total Solar Reflectance<\/u><\/em><\/strong>\u00a0– the amount of solar radiation that is reflected by a surface, measured as a percentage.<\/p>\n

Thermal Emittance<\/u><\/em><\/strong>\u00a0– the ability of a material to dissipate heat away from itself, or rather, to shed heat.<\/p>\n

Convection<\/u><\/em><\/strong>\u00a0– exchange of energy with air above the substrate.<\/p>\n

Conduction<\/u><\/em><\/strong>\u00a0– exchange of energy with the layer of the substrate directly below the surface.<\/p>\n

To better understand the phenomena of why colors display different heating\/cooling characteristics in sunlight, it is essential to examine the natural light spectrum. Solar radiation reaches the earth\u2019s surface in three distinct wavelength packets. These packets of light include Ultra Violet light (UVA 280 \u2013 315 nm, and UVB 315 \u2013 400 nm), Visible light (400 nm \u2013 700 nm) and Infrared light (near IR and far IR) between 700 and 2500 nm. The human eye sees light primarily in the visible portion of the light spectrum resulting in color. Some animal species, such as birds can see light in the UV portion of the spectrum.<\/p>\n

\"Microsoft
Figure 2 \u2013 Spectrum of solar radiance at the Earth’s surface.<\/figcaption><\/figure>\n

Figure 2 illustrates the natural spectrum of solar radiation. 5% of the light energy is UV light, 46% is visible light, and the remaining 49% is\u00a0infrared light energy.\u00a0Pigments<\/a>\u00a0can absorb or reflect\u00a0solar infrared energy<\/em>\u00a0resulting in 1) heat build-up of the coated substrate if the pigment absorbs IR energy (for example conventional darker pigments); or 2) little or no increase in temperature if the pigment reflects IR light (for example white and lighter colors).<\/p>\n

Solar infrared energy<\/em>\u00a0(700 \u2013 2,500 nm) is different than infrared energy emitted by hot objects in interior spaces, such as heaters. Infrared\u00a0energy is found in the far infrared range beyond 1,200 nm.<\/p>\n

Total Solar Reflectance\u00a0<\/em>(TSR) is the measurement of how much of the sun\u2019s energy an object reflects. TSR can be measured using a\u00a0Solar Spectrum Reflectometer.\u00a0<\/em>White pigments such as\u00a0titanium dioxide<\/a>\u00a0have a high solar reflectivity due to their white color, while conventional darker pigments have a lower TSR depending on how dark the pigment is.<\/p>\n

Solar reflective colored pigment technology<\/em>\u00a0uses specially designed doped ceramic (mixed metal oxides) pigments to achieve a higher degree of TSR than do conventional pigments of the same color. For example, the TSR of a dark brown conventional coating is about 8%, whereas the same color using solar reflective pigment technology will be about 28%. Typically, every one percent increase in TSR is accompanied by a one degree F drop in surface temperature. Colors using conventional pigments have a TSR in the range of 10 \u2013 20%, whereas\u00a0using SR pigments results in colors which have a TSR of 25% and higher.<\/p>\n

As Figure 3 illustrates, the TSR of Solar Reflective Paints is not affected by gloss or sheen as these later two properties are a measure of visible light reflectance and are independent of solar IR reflectance.<\/p>\n

\"SolarReflectanceFig3\"
Figure 3 \u2013\u00a0Comparison of solar reflectance of low and higher gloss coatings.<\/figcaption><\/figure>\n


\nEnvironmental benefits<\/em>\u00a0of Solar Reflective Paint Technology in architectural applications such as exterior roofs and sidewalls include:<\/p>\n