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.
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.
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.
Approximately 10% of the global population is expected to live in areas without regular access to electricity. The device could play a significant role in meeting cooling demands in areas with a lack of electricity or water.
The team suggests that the panels could be placed on top of a food storage container that requires an optimal cooling environment. Thus, reducing the chances of food spoilage and waste. And according to the study, this new system could increase the shelf-life of food by 40% in humid climates without electricity and by 200% in dry climates with minimal water refilling.
Even for evaporation, the water requirement is less. The water needs to be added once every four days in the hottest, driest areas and once a month in wet parts of the world, the official statement highlights.
Additionally, the device could improve the efficiency of existing air conditioning systems by supplying cold water (via pipes) to cool parts of the system.
Food waste and cooling systems
It is estimated that approximately 17% of the total food produced for human consumption is wasted. This figure is sufficient to feed around a billion individuals around the globe, as per the report. One of the major causes is a lack of effective refrigeration to maintain food quality.
The current food cold chain adds to greenhouse gas emissions. Cold chain technologies, as well as food loss and waste due to a lack of refrigeration, account for 4% of global greenhouse gas emissions.
Scientists and engineers have been working tirelessly to find long-term solutions to this problem. And this passive cooling system could be the key solution to this crisis.
Commercialization: a long road ahead
The device has several advantages, including the fact that it requires no electricity, uses little water and has a low carbon footprint. Amid the ongoing climate crisis, it could be a game changer. However, because the aerogel material is expensive to produce, it will take a long time to commercialize this unique product. The team suggests that more research is needed to find alternative solutions for aerogel for mass production.
“By combining evaporative cooling, radiative cooling, and insulation, it has a better cooling performance and can be effective in a wider range of climates than evaporative cooling or radiative cooling alone. The work could attract significant practical applications, such as in food preservation, if the system can be made at a reasonable cost,” said Xiulin Ruan, a mechanical engineering professor at Purdue University, who was not part of this research.
Images courtesy of Zhengmao Lu and Pexels