Cool White Polymer Coatings based on Glass Bubbles for Buildings

Area of Science:

• Materials Science
• Sustainable Building Technologies
• Optical Engineering

Background:

• Traditional selective emitter materials are often unsuitable for building applications due to cost or performance limitations.
• Effective passive cooling strategies are crucial for reducing building energy consumption and mitigating urban heat island effects.
• Developing advanced optical coatings is key to enhancing building energy efficiency and thermal comfort.

Purpose of the Study:

• To develop and evaluate a techno-economically viable optical coating for passive cooling applications in buildings.
• To investigate the relationship between glass bubble concentration and the optical properties (solar reflectivity, mid-infrared emissivity) of the polymer coating.
• To quantify the cooling performance, cost-effectiveness, and environmental impact of the developed coating on building surfaces.

Main Methods:

• Fabrication of polymer films with varying concentrations of integrated glass bubbles (0-70%).
• Measurement of optical properties, including selective solar reflectivity and mid-infrared emissivity.
• Outdoor performance testing on a concrete surface to assess temperature reduction and net cooling power.
• Economic analysis to determine cost per watt of cooling power.
• Estimation of potential annual energy and CO2 emission savings for typical buildings.

Main Results:

• The optical coating demonstrated a significant increase in selective solar reflectivity from 0.06 to 0.92 with increasing glass bubble concentration.
• Mid-infrared emissivity was maintained above 0.85, crucial for radiative cooling.
• Outdoor measurements showed a temperature reduction of up to 25°C and a net cooling power exceeding 78 W/m².
• The coating achieved a low cost of less than $0.005/W.
• Estimated annual energy savings of 2-12 MJ/m² and CO2 emission reductions of 0.3-1.5 kg/m² per building surface.

Conclusions:

• The developed glass bubble-integrated polymer coating is a techno-economically viable solution for passive building cooling.
• The coating offers significant daytime temperature reduction and substantial energy and CO2 savings, particularly for buildings with high surface-area-to-volume ratios.
• This technology presents a promising approach to improve thermal comfort and reduce cooling demands in existing and new buildings, including those without air conditioning.