Radiative Cooling: Redefining Air-conditioning Systems
Radiative cooling is the natural process through which objects shed heat in the form of infrared (IR) radiation. All materials at room temperature emit infrared at wavelengths of 5–15 μm. However, the process is typically not very efficient because it is counteracted by external influences that heat the object, such as sunlight and air currents. Air, meanwhile, absorbs and emits very little radiation with wavelengths 8–13 μm. The Earth cools itself at night by emitting infrared through this “atmospheric window” into space.
The three geniuses, Dr. Ronggui Yang, Ph.D, MIT, Dr. Xiaobo Yin, Ph.D, Stanford and Dr. Gang Tan, Ph.D, MIT has developed a new metamaterial film that provides cooling without needing a power input. Made out of glass microspheres, polymer and silver, the material uses passive radiative cooling to dissipate heat from the object it covers. It emits the energy as infrared radiation and also reflects solar light. Most importantly, the material will be scalably manufactured at low-cost through roll-to-roll manufacturing processes.
- Passive cooling technology dissipate heat from Earth into outer space (3 K) as infrared radiation through the atmospheric transparency window (8–13 μm).
- A hybrid glass microsphere-plastic metamaterial film that is fully transparent to the solar spectrum while having an infrared emissivity greater than 0.93 across the atmospheric window has been developed.
- It cools objects underneath the radiative cooling film to 10 K and 16 K below ambient during day-time and night-time, respectively.
- When integrated with silicon photovoltaic cells, it increases its efficiency by 5% (absolute efficiency gain of 0.5-1% due to more than 10 K cooling) and increases its lifetime.
- Applying the film directly on the roof could save air conditioner energy use by more than 30%.
Think Green Limited is keeping in touch with the project from the present status and will be introducing the material in Bangladesh as soon as it commercially available.