Cooling and heating homes and buildings consume a significant amount of energy; therefore, finding innovative techniques to regulate temperature passively is critical. Thankfully, engineers in Germany and China have created a new wood-based foam that can drastically cool buildings to a comfortable temperature and can be easily tuned.
Although air conditioning is efficient, it is not the most environmentally friendly cooling method. Scientists have created solutions in recent years that use less energy, including:
- mirror coatings that reflect sunlight,
- super-white paints that reflect 98.1% of sunlight,
- radiative cooling systems that emit a building’s heat as infrared waves into the sky, where it passes through the atmosphere and vents into the cold of outer space, and 3D-printed porous ceramic cubes that lower indoor air temperatures by up to 7°C through evaporation alone.
However, the efficiency of these techniques varies depending on the conditions. For example, reflective coatings can still let heat in when it’s exceptionally hot or humid, while radiative cooling is less effective when it’s cloudy. It can also be challenging to tune the cooling level.
Scientists from Nanjing Forestry University and the University of Göttingen have developed a novel material that, according to them, addresses some of these issues. It’s a foamy wood substance that reflects sunlight, works as thermal insulation, and returns absorbed heat to the atmosphere. It’s made of cellulose nanocrystals joined by a silane bridge and then freeze-dried into a white, lightweight foam. The finished product reflects 96% of visible light from the Sun and emits 92% of the infrared radiation it absorbs.
The researchers put the material over an aluminum foil-lined box and placed it in direct sunlight at midday to evaluate its cooling properties. The material kept the box’s interior 9.2°C (16.5°F) colder than the outside air, and even in humid conditions, it kept the inside 7.4°C (13.3°F) cooler. The scientists believe that if scaled up to line the walls and roof of a building, it may reduce cooling energy consumption by 35% on average. The research was published on May 5, 2022, in Nano Letters.
Most interestingly, when the foam was squeezed, its cooling power dropped. This may sound like a downfall, but the researchers believe compressing the foam could be valuable to fine-tune the level of cooling required by the environment or weather conditions. According to the researchers, the new cooling foam paves the way for thermal-regulating materials that are environmentally friendly and could considerably reduce the cost of energy used for cooling.
