West LA Times

Researchers at UCLA have identified a novel mechanism to cool buildings while conserving energy. A study led by Aaswath Raman, an associate professor of materials science and engineering at the UCLA Samueli School of Engineering, demonstrates a new passive cooling technology that involves coating walls and windows with materials that better manage heat movement between buildings and their surroundings at ground level.

The research, published in Cell Reports Physical Science, addresses the challenge of cooling buildings with less skyward-facing surfaces. These structures are typically harder to cool due to their retention of heat from the ground and neighboring walls during high temperatures and difficulty in warming during colder seasons.

“If we look at historical cities like Santorini in Greece or Jodhpur in India, we find that cooling buildings by making roofs and walls reflect sunlight has been practiced for centuries,” said Raman. “In recent years there has been massive interest in cool roof coatings that reflect sunlight. But cooling walls and windows is a much more subtle and complex challenge.”

By using super white paint on roofs to reflect sunlight, researchers have previously achieved passive radiative cooling effects. The team aimed to replicate this effect on walls and windows using materials capable of preferentially absorbing and emitting radiant heat within the atmospheric window. They found that such materials could maintain cooler temperatures than conventional building materials in summer while staying warmer during winter.

“We were particularly excited when we found that materials like polypropylene, which we sourced from household plastics, can selectively radiate or absorb heat in the atmospheric window very effectively,” Raman noted. “These materials border on the mundane, but the same scalability that makes them common also means that we could see them thermoregulating buildings in the near future.”

The proposed mechanism is entirely passive, potentially reducing reliance on air conditioners and heaters which are costly to run and contribute to carbon dioxide emissions. "The mechanism we proposed is completely passive, which makes it a sustainable way to cool and heat buildings with the seasons and yield untapped energy savings," said Jyotirmoy Mandal, first author of the study.

This approach holds promise for low-income communities with limited access to heating or cooling systems. The team plans further exploration into demonstrating this effect at larger scales and its real-world energy savings impact.

Funding for the study came from Schmidt Science fellowship, Rhodes Trust, Alfred P. Sloan Foundation, and National Science Foundation. Co-authors include John Brewer (UCLA), Jyothis Anand (Oak Ridge National Lab), Arvind Ramachandran (Arizona State University), Sagar Mandal (independent researcher).