Ways to keep buildings cool with improved super white paints

Date:
July 9, 2020
Source:
University of California - Los Angeles
Summary:
Materials scientists have demonstrated ways to make super white
paint that reflects as much as 98% of incoming heat from the
sun. The advance shows practical pathways for designing paints
that, if used on rooftops and other parts of a building, could
significantly reduce cooling costs, beyond what standard white
'cool-roof' paints can achieve.



FULL STORY ==========================================================================
A research team led by UCLA materials scientists has demonstrated ways
to make super white paint that reflects as much as 98% of incoming heat
from the sun.

The advance shows practical pathways for designing paints that, if used
on rooftops and other parts of a building, could significantly reduce
cooling costs, beyond what standard white 'cool-roof' paints can achieve.


==========================================================================
The findings, published online in Joule, are a major and practical
step towards keeping buildings cooler by passive daytime radiative
cooling -- a spontaneous process in which a surface reflects sunlight
and radiates heat into space, cooling down to potentially sub-ambient temperatures. This can lower indoor temperatures and help cut down on
air conditioner use and associated carbon dioxide emissions.

"When you wear a white T-shirt on a hot sunny day, you feel cooler than
if you wore one that's darker in color -- that's because the white shirt reflects more sunlight and it's the same concept for buildings," said
Aaswath Raman, an assistant professor of materials science and engineering
at UCLA Samueli School of Engineering, and the principal investigator
on the study. "A roof painted white will be cooler inside than one in a
darker shade. But those paints also do something else: they reject heat
at infrared wavelengths, which we humans cannot see with our eyes. This
could allow buildings to cool down even more by radiative cooling."
The best performing white paints currently available typically reflect
around 85% of incoming solar radiation. The remainder is absorbed by
the chemical makeup of the paint. The researchers showed that simple modifications in a paint's ingredients could offer a significant jump, reflecting as much as 98% of incoming radiation.

Current white paints with high solar reflectance use titanium oxide. While
the compound is very reflective of most visible and near-infrared light,
it also absorbs ultraviolet and violet light. The compound's UV absorption qualities make it useful in sunscreen lotions, but they also lead to
heating under sunlight -- which gets in the way of keeping a building
as cool as possible.

The researchers examined replacing titanium oxide with inexpensive and
readily available ingredients such as barite, which is an artist's
pigment, and powered polytetrafluoroethylene, better known as
Teflon. These ingredients help paints reflect UV light. The team also
made further refinements to the paint's formula, including reducing the concentration of polymer binders, which also absorb heat.

"The potential cooling benefits this can yield may be realized in the near future because the modifications we propose are within the capabilities
of the paint and coatings industry," said UCLA postdoctoral scholar
Jyotirmoy Mandal, a Schmidt Science Fellow working in Raman's research
group and the co- corresponding author on the research.

Beyond the advance, the authors suggested several long-term implications
for further study, including mapping where such paints could make
a difference, studying the effect of pollution on radiative cooling technologies, and on a global scale, if they could make a dent on the
earth's own ability to reflect heat from the sun.

The researchers also noted that many municipalities and governments,
including the state of California and New York City, have started to
encourage cool-roof technologies for new buildings.

"We hope that the work will spur future initiatives in super-white
coatings for not only energy savings in buildings, but also mitigating
the heat island effects of cities, and perhaps even showing a practical
way that, if applied on a massive, global scale could affect climate
change," said Mandal, who has studied cooling paint technologies for
several years. "This would require a collaboration among experts in
diverse fields like optics, materials science and meteorology, and
experts from the industry and policy sectors."

========================================================================== Story Source: Materials provided by
University_of_California_-_Los_Angeles. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Jyotirmoy Mandal, Yuan Yang, Nanfang Yu, Aaswath P. Raman. Paints
as a
Scalable and Effective Radiative Cooling Technology for
Buildings. Joule, 2020; DOI: 10.1016/j.joule.2020.04.010 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200709141629.htm

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