Research at the Lawrence Berkeley National Laboratory holds the potential for a new type of dark reflective surface that will keep both buildings and vehicles cooler.
Scientists experimenting with synthesized ruby crystals and pigments have shown that a dark roof coating can reflect heat as effectively as a white roof, the lab said in a news release. The research holds promise for reducing cooling loads in buildings and vehicles and mitigating the urban heat island effect, the collective heat generated by dark surfaces in a dense, urban environment.
Researchers tested the idea by coloring cool roof coverings with ruby red, which the lab described as aluminum oxide doped with chromium. Then they synthesized ruby pigment to mix into coatings, and found that white surfaces treated with these paints stayed as cool as white materials.
The results enhanced previous work to make darker surfaces more reflective of heat.
“Over the past 15 years, Heat Island Group researchers have used special pigments that strongly reflect invisible ‘near-infrared’ light to make dark surfaces that stay cooler in the sun than conventional dark surfaces, though still not as cool as white surfaces,” the lab said. “This new work shows that fluorescent cooling can boost the performance of these pigments by re-emitting at longer wavelengths some of the visible light that the surface must absorb to appear dark.”
The lab hopes the work, if commercialized, could be applied to coatings for a number of products and materials. Synthetic ruby crystals were available online and were “surprisingly inexpensive.”
Manufacturers such as CertainTeed already produce roofing products with higher solar reflectance than conventional roofing, such as its Presidential Solaris brand. But Berkeley Lab researchers said the use of fluorescence for cool materials is a new concept.
Their findings were published in the journal Solar Energy Materials & Solar Cells.