A recent study led by researchers at UCLA and Princeton has unveiled a novel, passive cooling technology that promises to transform how buildings are heated and cooled. This new method involves coating walls and windows with materials that can effectively manage the movement of radiant heat between buildings and their surroundings at ground level. This approach could significantly reduce reliance on traditional air conditioning systems, offering a more sustainable and cost-effective solution, especially for low-income communities with limited access to cooling and heating systems.
Understanding the New Cooling Mechanism
The research, published in Cell Reports Physical Science, demonstrates that common building materials can be engineered to selectively absorb and emit radiant heat within the atmospheric window. This allows these materials to stay cooler in the summer and warmer in the winter compared to conventional materials. By using materials like polypropylene, sourced from household plastics, the researchers have found a scalable and affordable way to regulate building temperatures passively.
Historical and Current Cooling Techniques
Historically, buildings have been cooled by reflecting sunlight off roofs and walls, a practice seen in cities like Santorini, Greece, and Jodhpur, India. Modern approaches include the use of cool roof coatings and window shades. However, cooling walls and windows has remained a complex challenge. The new method builds on these traditional techniques by enhancing the thermal management capabilities of building materials.
Building Cooling Methods Compared
While each cooling method has its benefits, reflective coatings and cool roof technologies offer significant energy savings and are effective in reducing heat absorption. Passive radiative cooling is a promising new technology with potential for even greater efficiency, though it may come with higher initial costs. Window shades are a cost-effective solution for reducing solar heat gain through windows but are less effective in addressing overall building heat load.
Reflective Coatings
Reflective coatings, such as cool roof technologies, are designed to reflect solar radiation, reducing heat absorption by buildings. These coatings can reflect up to 98% of sunlight, significantly reducing the heat load on a building[6]. The effectiveness of these coatings depends on their ability to reflect both visible and near-infrared light, which can help mitigate the urban heat island (UHI) effect and reduce cooling energy demands in urban areas[10]. In a test conducted in Phoenix, a building with a specialized reflective coating consumed 20% less energy compared to a neighboring building with a standard commercial reflective coating[6]. The cost of these coatings varies, but they generally provide a cost-effective solution for reducing energy consumption in hot climates.
Window Shades
Window shades are a common method for blocking direct sunlight and reducing indoor temperatures. While they are effective in minimizing solar heat gain through windows, their overall impact on building energy efficiency is less significant compared to reflective coatings or cool roof technologies. The cost of window shades is relatively low, making them an accessible option for many homeowners. However, their effectiveness is limited to specific areas of a building and does not address heat gain through roofs or walls.
Cool Roof Technology
Cool roof technology involves using materials that reflect more sunlight and absorb less heat. These roofs can reflect about 80% of sunlight, with newer technologies aiming to reflect up to 98%[6]. The Cool Roof Rating Council lists over 600 roof coatings with a solar reflectance of 80% or better, indicating a wide range of available products[6]. Cool roofs can significantly reduce cooling energy costs, especially in hot climates, and are increasingly popular due to rising energy prices. The cost of implementing cool roof technology can vary, but it often pays for itself through energy savings over time.
Passive Radiative Cooling
Passive radiative cooling is a newer method that uses coatings to manage heat movement at the ground level, offering energy savings and enhanced thermal comfort. These coatings not only reflect sunlight but also emit infrared radiation, effectively cooling the surface they are applied to[6]. This method can provide substantial energy savings, as demonstrated by the EnKoat start-up, which reported a 20% reduction in energy consumption in a yearlong test[6]. The cost of passive radiative cooling systems can be higher initially due to the advanced materials used, but the long-term energy savings and improved thermal comfort can justify the investment.
Future Implications
The potential energy savings from this new mechanism are substantial, comparable to the benefits of painting dark roofs white. This method could be particularly beneficial in heat-vulnerable communities, providing an equitable solution as global temperatures rise. The research team, led by Aaswath Raman, plans to continue exploring this technology at larger scales to assess its real-world energy savings.
Funding for this study was provided by the Schmidt Science Fellowship, the Rhodes Trust, the Alfred P. Sloan Foundation, and the National Science Foundation.
Read More
[1] https://newsroom.ucla.edu/releases/researchers-discover-mechanism-cool-buildings-saving-energy
[2] https://www.enn.com/articles/75057-researchers-discover-new-mechanism-to-cool-buildings-while-saving-energy
[3] https://www.techexplorist.com/new-method-cool-buildings-while-saving-energy/87128/
[4] https://techxplore.com/news/2024-08-corrugated-wall-passively-cool.html
[5] https://scitechdaily.com/princeton-scientists-develop-passive-mechanism-to-cool-buildings-in-the-summer-and-warm-them-in-the-winter/
[6] https://cen.acs.org/business/specialty-chemicals/cool-coatings-combat-climate-change/101/i35
[7] https://efficiencymatrix.com/understanding-solar-thermal-reflective-paints-cool-roof-busting-myth/
[8] https://www.sciencedirect.com/science/article/abs/pii/S2210670724004505
[9] https://www.mdpi.com/2079-6412/12/1/7
[10] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9413095/
