Beijing time on December 1st, according to the Science Daily, engineers at Stanford University in the United States invented a revolutionary coating material that can help cool buildings, even during sunny daylight hours. The main working principle of this invention is to radiate the heat of the building and reflect it directly into space. This new ultra-thin multi-layer material cools buildings without the need for air conditioning, reflecting sunlight to reduce heat entering the building while reflecting heat inside the building into space.
This new ultra-thin multi-layer material cools buildings without air conditioning
This energy-saving breakthrough, led by Stanford University's electrical engineering professor Shanhui Fan and research assistant Aaswath Raman, was published in the journal Nature. At the heart of this invention is an ultra-thin, multi-layered material that treats visible and invisible sunlight in a novel way.
Invisible light in the form of infrared radiation is one of the ways in which all objects and organisms release heat. When we stand in front of a closed oven, the heat we can feel without touching us is infrared light. This invisible, thermally conductive light is the light that is shunted from buildings and reflected into space in the latest Stanford research group.
Of course the sun will also heat the building. In addition to being able to process infrared light, this latest material can also be used as an incredibly efficient mirror that reflects almost all incident light. The result is the so-called photon radiant cooling by the Stanford research team that both “unloads†the infrared heat in the building and reflects the sunlight that heats the building. This results in a building that is less cooled and requires less cooling.
“This is a very new but very simple idea,†said Professor of Electrical and Computer Science at the University of California at Berkeley, a pioneer in the field of photonic crystals, and Eli Jabronovic, who leads the Center for Energy Efficiency Electronic Science (Eli Yablonovitch) said this. “Thanks to Prof. Fan’s research, we can now use not only radiant cooling at night, but also counter-intuitive use during the day.â€
Researchers say the cost-effective materials they designed are suitable for large-scale deployment on building roofs. Although it is still a very young technology, they believe that one day this technology can help reduce the need for electricity. 15% of the energy used in American buildings is used in air conditioning systems.
In practice, the researchers believe that the coating can be plated on a harder material so that it can tolerate this element. “The research team also showed how to passively cool the structure by radiating heat into the cold and dark space.†Stanford University Honorary Professor, former director of the SLAC National Accelerator Laboratory (referred to as SLAC, formerly known as the Linear Accelerator Center), Nobel Physics physicist physicist Burton Richter said.
Research lead author Roman said that a warm world requires cooling without power. “For all developing countries, photon radiant cooling not only caters to the ever-increasing air conditioning needs of urban areas, but also enables off-grid cooling in some rural areas.â€
Window facing the space
The real breakthrough is how the material invented by Stanford radiates energy from buildings. It is well known that heat can be delivered in three forms: conduction, convection, and radiation. Conduction is the transfer of energy through contact, which is why you must wear gloves to touch the hot baking tray. Convection is the transfer of heat through the movement of air or fluid, which is the warm gas that comes up when the oven is turned on. Radiation transfers heat in the form of infrared light.
The latest coating structure is to radiate thermally conductive infrared light directly into space. This ultra-thin coating is set to illuminate the heat-conducting infrared light in the building at a precise frequency and through the atmosphere without heating the air, a feature that takes into account the danger of global warming. "It's like having a window that opens into space," Fan said.
Aiming at the mirror
But transferring heat to space is not enough. This multi-layer coating also acts as a highly efficient mirror that blocks 97% of the sunlight that illuminates the building. "We created something that is both a radiator and a reflection," Roman said. The combination of radiation and reflection causes daytime photon radiation to cool at a temperature that is 9 degrees Fahrenheit lower than ambient air.
This multilayer material is only 1.8 microns thick and thinner than the thinnest aluminum foil. It consists of seven layers of silica and cerium oxide, the latter being placed on a thin silver layer. These layers of material do not have a uniform thickness, but are specifically designed to form a new material. Its internal structure is set to radiate infrared rays at a specific frequency so that the infrared rays can directly enter the atmosphere without heating the air near the building.
“This photon approach allows us to precisely adjust solar reflections and infrared thermal radiation,†said Linxiao Zhu, a research associate and Ph.D. student in applied physics. “I am very excited about the results of these studies (Stanford University research team),†said Marin Soljacic, a professor of physics at the Massachusetts Institute of Technology. “This is nanophotonic ability. A great example."
From prototype to building panel
To actually promote photon radiant cooling, at least two technical problems need to be solved. The first is how to transfer the heat inside the building to the entire outer coating. Once the heat reaches a given location, the coating can scatter heat into space, but engineers must first determine how efficiently to transfer heat from the building to the location of the coating material.
The second issue is production. At present, the prototype size of the Stanford research team is only equivalent to a pizza for one person. Cooling the building requires huge panels. Researchers say that large-scale production equipment can achieve the required panel size.
Cosmic refrigerator
From a broader perspective, the research team believes that this project is the first step towards using the cold of space as a resource for vanity. Just as sunlight can be a renewable source of solar energy, the cold universe can also provide a wide area to reduce heat.
“Every object that generates heat transfers heat to the radiator,†Fan said. “What we are doing is creating a new way that allows us to take advantage of the cold of the universe as a radiator for the day.â€
In addition to Professor Fan, Roman and Zhu, other co-authors of the study include Marc Abou Anoma, a graduate student in mechanical engineering, and Eden Lafay, a graduate student in applied physics. Eden Rephaeli. The study was funded by the US Department of Energy's Advanced Research Project Agency-Energy (ARPA-E).
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