Ce qu'il fait
Designed for temperate climates in need of deployable cooling, (Sub)Ambient provides over 5°C of electricity-free cooling even in direct sunlight, without the harmful side effects of urban heat islands, high electricity bills, or ozone-destroying refrigerants.
Votre source d'inspiration
In 2023, the world experienced its hottest year on record, with temperate climates like London facing unprecedented extreme heat. Our international team, living in London at the time, had to endure this unbearable weather. As students, purchasing an AC unit for a few weeks was neither affordable nor environmentally justifiable. Painting the exterior with a permanent cooling coating wasn’t an option either, as we didn’t own the flat and needed it to retain heat in winter. So, leveraging our material science backgrounds, we decided to develop a deployable passive cooling material inspired by how the Saharan silver ant stays cool in the desert.
Comment ça marche
(Sub)Ambient makes use of a natural phenomenon called Passive Daytime Radiative Cooling, exhibited by the Saharan silver ant, whose reflective and emissive properties enable it to survive in one of the hottest environments on Earth. The key components of (Sub)Ambient are a densely packed matrix of reflective CaCO3 microspheres and an ultra-porous and emissive cellulose nanofiber network. Both materials act like microscopic mirrors, scattering sunlight internally until it is reflected away. Because (Sub)Ambient reflects almost all sunlight, even in direct sun, it doesn’t heat up. This material combination also emits infrared radiation that passes through what is known as the Atmospheric Window. Most heat on Earth is trapped by the atmosphere, but infrared radiation with a frequency of 8–13 µm (the Atmospheric Window) is not absorbed by the gases surrounding Earth. Thus, when exposed to the sky, (Sub)Ambient can become over 5°C colder than the surrounding air.
Processus de conception
We began by analyzing state-of-the-art passive daytime radiative cooling options. We found that existing coating or film solutions are often unsuitable for temperate climates and lack accessibility and sustainability due to the materials and manufacturing techniques used. Inspired by the Saharan silver ant, we identified a more accessible strategy by combining a dense matrix of highly reflective particles with an ultra-porous and emissive polymer network. After exploring particle options like BaSO4, SiO2, and TiO2, we chose CaCO3 for its abundance as shell waste, eco-friendliness, and high reflectivity and emissivity. Through many digital simulations and ball milled samples, we determined the optimal particle sphere size combinations for max density. To bind these particles, we chose nanocellulose over other natural polymers due to its nanopore-forming ability when pressed, its abundance as kombucha industry waste, biodegradability, and high emissivity in the Atmospheric Window. We varied the levels of each component, then heat-pressed to form sheet samples, testing for stability, flexibility, and cooling. We also tested different forming molds to create geometries that enhance cooling. The current surface topology is the result of biomimicry and several Ansys Fluent simulations.
En quoi est-il différent ?
Similar passive daytime radiative cooling products include: permanent coatings and complex multilayer photonic films. Permanent coatings pose challenges in temperate climates with cold, non-summer months, as they cannot be removed. This leads to excessive cooling during winter, increasing the electricity needed to warm the building and negating the cooling cost savings achieved in summer. Additionally, these coatings often require specific substrates, limiting their suitability for many common structures. Complex multilayer photonic films, though removable, are costly and energy-intensive to produce, often requiring precious metals and advanced techniques like laser metal deposition. (Sub)Ambient distinguishes itself with accessible manufacturing methods, such as milling and heat pressing, and formable geometry to fit different contextual needs. It is also biodegradable at the end of its life cycle and utilizes readily available, cost-effective waste materials.
Plans pour l'avenir
Our team is preparing to advance from lab and small-scale outdoor trials to a full-scale test site in the summer of 2025. To achieve this, we need to refine our material composition to withstand occasional heavy summer rain. We are conducting trials with varying levels of moisture-resistant additives that still maintain the material's passive cooling abilities. Each sample is systematically tested to identify the ideal composition for the upcoming test site. Additionally, given the versatility of our material, we are exploring new form factors for specific contexts, such as peat bog conservation and shelter for volunteer wildfire fighters.
Récompenses
IF Student Design Award 2024
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