New MIT passive cooling system works without electricity
With rising temperatures, humans have become more reliant on cooling technology to maintain stable temperatures. As a result, buildings are using more energy to cool, and urban areas are particularly vulnerable due to the urban heat island effect. The Massachusetts Institute of Technology (MIT) has developed a new passive cooling device for buildings to help with this.
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In 2019, the cooling sector accounted for 8.5% of global electricity consumption, equal to more than one gigatonne of carbon dioxide emissions. With such rising demand, it is critical to seek out sustainable alternatives.
Related: Recycled shipping container cafe utilizes passive cooling in India
MIT’s technique combines efficient design and technology to cool a building without the use of electricity.
Passive cooling strategy
The team placed the newly-built device over a small area of the MIT campus’s rooftop to test its performance. The results showed that in direct sunlight, this cooling device cooled the area beneath the panel to 9.3 degrees Celsius (48.74 degrees Fahrenheit) below ambient temperature.
The team has been working on this device for a long time and has advanced with technology to achieve unprecedented cooling. The device applies known principles of evaporative and radiative cooling. Evaporative cooling uses evaporated water to cool hot air, whereas radiative cooling, unlike air conditioners that emit heat directly to outer space rather than the surrounding environment.
“The novelty here is really just bringing together the radiative cooling feature, the evaporative cooling feature, and also the thermal insulation feature all together in one architecture,” said Zhengmao Lu, an MIT postdoc, who was part of this new study.
Design of the new device
The new, slim device resembles a standard solar panel in design. The system is then made up of several layers that serve as a reflector, evaporator and insulation. This together allows cooling while water and heat pass through the device.
The top layer is made of highly insulating aerogel, which is “mostly air enclosed in the cavities of a sponge-like structure made of polyethylene.” The material aids the passing of water vapor and radiation. It also limits the solar heating of the device.
Beneath this, another sponge-like hydrogel layer is immersed in water for evaporative cooling. The statement explains how the water in the hydrogel heats up and converts to water vapor. In turn, it rises upward (evaporative cooling), carrying some of the heat in the process.
The team has also added a mirror-like layer to bounce back any incoming sunlight, without heating the device materials and reducing their thermal load.