From the Lab of Prof. Aaswath Raman
BACKGROUND
Prof. Aaswath Raman and his research team in UCLA’s Department of Materials Science and Engineering have developed a number of technologies that have the potential of greatly improving energy efficiency of buildings through reduced heating and cooling. Energy consumption in residential and commercial buildings contributes up to 30% of total greenhouse gas emissions worldwide. In the United States, the buildings sector accounts for 41% of primary energy consumption, of which heating and cooling are responsible for over 35%.
BIOGRAPHY
Aaswath Raman is Assistant Professor of Materials Science and Engineering at UCLA. His research interests include metamaterials, nanophotonics, machine learning and renewable energy systems. He was previously an Assistant Professor of Electrical and Systems Engineering at the University of Pennsylvania, and a Research Associate at Stanford University.
Prof. Raman received his Ph.D. in Applied Physics from Stanford University in 2013, and his A.B. cum laude in Physics and Astronomy and Astrophysics, and M.S. in Computer Science from Harvard University in 2006. In 2015, he was recognized as one of MIT Technology Review’s prestigious “Innovators Under 35” (https://www.technologyreview.com/innovator/aaswath-raman/). He has published more than 25 peer-reviewed articles in leading journals including Nature, Nature Energy and Physical Review Letters. Prior to obtaining his Ph.D. he was a program manager at Microsoft working on machine learning algorithms that can detect spam in web search results. He is also a co-founder and Chief Scientific Officer of SkyCool Systems, a startup commercializing daytime radiative cooling technology he originated. Prof. Raman has given over 30 invited talks around the world, including to broad global audiences at TED 2018 and La Ciudad de las Ideas.
Aaswath Raman group website: http://www.aaswathraman.com/
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UV-Reflective Paints with High Overall Solar Reflectance for Passive Cooling of Buildings
Thermally radiative materials refer to materials and methods in which the thermal radiation emissions from a surface are able to be controlled spectrally and spatially. Coatings, as a production method, possess a clear advantage with respective to cost and simplicity. “Cool” white exterior coatings reflect sunlight (0.3-2.5 μm) and radiate heat (4-40 μm, particularly 8-13 μm) into the outer space. In doing so, they have a net passive cooling effect and are a sustainable alternative to air-conditioners to cool buildings and outdoor structures. However, the cooling performance of traditional “cool” exterior coatings suffers from material limitations, primarily the absorption of UV light, lowering their cooling efficiency. New types of exterior coatings are needed to optimize reflectivity > 0.94 and improve cooling performance.
This invention presents an external coating with exceptional solar-UV reflectance. The coating can be applied by a painting, spraying, dip-coating or other simple techniques. Upon drying, the coating, in sufficient thicknesses, can achieve solar reflectance from 0.94-0.98. With a high overall solar reflectance and high thermal emittance, this coating is ideal for passive daytime radiative cooling of buildings.
Reference: UCLA Case No. 2020-464
Patent Application Filed
Relevant Publication: Mandal, Jyotirmoy, et al. "Hierarchically porous polymer coatings for highly efficient passive daytime radiative cooling." Science 362.6412 (2018): 315-319.
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Tuning Radiative Heat Flows Between Interior Surfaces and Human Occupants to Improve Heating and Cooling Efficiency
While thermal comfort is linked to the air temperature in a conditioned space, it is also tied to a number of other factors. One such factor is how the heat that is generated by the human body is either absorbed into or reflected from the materials surrounding a person. During cold weather, decreasing the amount of heat lost from a room’s occupant into surrounding materials is desirable, whereas during warm weather, occupant comfort can be improved by increasing the amount of body heat dissipated into a room’s surfaces, as these surfaces are typically cooler than skin temperature.
This invention introduces dynamic emissivity surfaces for interior spaces that can be tuned to improve heating and cooling of a building. The surfaces have already been developed and successfully demonstrated a decrease in the required set point temperature of a room by 7°C, while maintaining occupant comfort. This corresponds to an energy savings of 67.7% in heating during cold weather and a 38.5% energy savings during warm weather. By being able to adjust a person’s environment in response to varying heat loads and conditions, these interior surfaces can maximize energy efficiency and decrease energy consumption year round.
Reference: UCLA Case No. 2020-187
Patent Application Filed
Relevant Publication: Xu, Jin & Raman, Aaswath. (2020). Tuning radiative heat flows between interior surfaces and human occupants to improve heating and cooling efficiency. 10.36227/techrxiv.11862696.v2.
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Spectrally Selective Thermal Radiators for Cooling of Vertical or Horizontal Surfaces with Limited View of the Sky
Passive radiative cooling (PRC), a process where objects on Earth radiate heat into outer space, is a promising method for cooling buildings and surfaces exposed to the sky. As a potential alternative to air-conditioners, the effectiveness of PRC has been severely limited due to available view (exposure) of these surfaces to the sky. In addition, PRC heat loss occurs only at wavelengths in the thermal window of the atmosphere, but heat gain occurs across all thermal wavelengths. The resulting heat gain radiated from nearby objects is typically greater than the heat loss through PRC, resulting in buildings heating up, even when not exposed to direct sunlight. For PRC to be a viable cooling method, innovations are needed for its use with surfaces with a limited view of the sky and exposure to thermal radiation.
The invention presents a method for achieving passive radiative cooling in vertical (e.g. walls of buildings) and horizontal (e.g. roofs) surfaces with limited view of the sky. The method uses selective emitters made of polymer coatings on metal, which are highly scalable, cheaply manufactured and easily applied onto surfaces. The emitter absorbs and emits in specific portions of the infrared wavelengths, allowing for lower steady-state temperatures and, in most situations, a net cooling effect even with limited view of the sky. The polymer composition can be modified for application. By restricting heat loss and gain only to specific wavelengths, a large amount of radiative heat from terrestrial sources is reflected, enabling a higher degree of cooling.
Reference: UCLA Case No. 2020-388
Patent Application Filed
Relevant Publication: Mandal, J., Jia, M., Overvig, A., Fu, Y., Che, E., Yu, N. and Yang, Y., 2019. Porous Polymers with Switchable Optical Transmittance for Optical and Thermal Regulation. Joule.
Relevant Articles: https://www.washingtonpost.com/climate-solutions/2020/10/07/radiative-cooling-climate-change/