Page 26 - Green Builder Sept-Oct 2020 Issue
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Making the ‘MOST’ of sunlight. Scientists from Chalmers University of Technology in Sweden have developed a molecular solar thermal (MOST) window film
that can absorb energy from the sun’s rays and later emit it as heat for up to eight hours after sunset. CREDIT: YEN STRANDQVIST¤CHALMERS
some new smart window models simply use coatings that o er RADIANT IDEAS
similar—but o ine—features like auto-shading. Smart window One of the most fascinating new developments in refrigerant
coatings are essentially lled with very small, water- lled balls that technology involves the concept of radiative cooling…yet another
shrink or expand with temperature. One academic team published interesting take on generating energy from the world around us.
in the science journal Joule revealed that their lm of microscopic But given that the concept implies a sky-facing surface should be
particles alone could reduce temperature (without a loss of visibility) cooler than the air around it, does that not also imply a plausible
by as much as nearly degrees Fahrenheit. The coat reportedly connection for our cooling needs?
reects up to percent of the sun’s heat while letting in visible Indeed it does. Because heat escapes along a thermal gradient
light, freeing up more of our energy from use on air conditioning. leading out into the cold of space from the surface(s) of our planet,
Some researchers have been hard at work producing a do-it- this has led some scientists to conclude that we might build materials
yourself (DIY) paint-on coating version of the aerogel tech, o ering to recycle the slight dip in surface-level temperature. And by setting
homeowners an energy-ecient window coating at one-tenth the up a specially structured reective material, scientists were recently
cost of professionally installed retro ts. able to direct a wavelength of light back out into space that escapes
our atmospheric cover more easily—leading to a radiative cooling
HEATING UP TO STAY COOL e ect even during the day. As a result, a material able to direct unique
We may even be able to capture the thermal energy of incoming wavelengths more readily can become about degrees Celsius cooler
sunlight streaming through our windows, and—rather than than ambient air temperatures.
harnessing the electricity through TSC—use materials similar to A similar device was also developed by scientists at the University
the thermal energy “hybrid” panels to retain it. To recap, thermal of Bu alo. It requires no added electricity to function. The system
hybrid panels will soon be capable of placement on rooftops as is essentially a low-cost polymer/aluminum lm installed inside a
traditional solar panels are, but they would capture thermal energy box located at the bottom of a solar “shelter.” The lm performs
for immediate or (through storage) later use. radiative cooling and keeps ambient air within the shelter cool by
The device may bridge our much-needed gap in “solar+storage” re-directing more of the surrounding heat—with a sky-facing design
technology. In terms of window tech, one new lm with a uniquely that actively channels thermal radiation more directly from the lm
designed molecular chemistry now offers an ability to capture into the atmosphere. The device helps to corral and focus directed
thermal energy from solar rays and distribute it evenly throughout heat away from ambient surroundings without any use of electricity.
the glass. Materials have a yellowish tint at the start of the day, According to the team’s research, temperature reductions around
isomerize and turn transparent in response to solar heat, then reverse the enclosed space dropped by about °C (°F) during the day and
over time at night to re-start the cycle. °C (about °F) at night.
As long as the sun is shining on the window’s lm, less heat can One geoengineering initiative falling under a category of solar
penetrate into rooms. But the added bonus is that heat can be stored radiation management (SRM) includes painting our rooftops
for much longer periods than just hours, or even days. Researchers colors that reect away more sunlight to reduce the amount of heat
envisioned that by using a molecular solar thermal (MOST) storage absorbed. So-called “cool roof” coatings can not only reduce the
system, homeowners may be able to store thermal energy for weeks amount of heat warming up a home, but also slightly reduce the
or even months. surrounding air temperature—particularly if many homes in an area
24 GREEN BUILDER September/October 2020 www.greenbuildermedia.com
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