Cheaper radiative cooling paint by milling larger glass bubbles

Abstract

Radiative cooling technology potentially can be applied to buildings to reduce cooling energy consumption. One general approach to making radiative cooling paints is to mix polymers with reflective materials. However, the high cost of materials has limited the large-scale application of radiative cooling in real scenarios. In this work, we propose another method to make high-performance radiative cooling paint, at a lower cost. This method entails ball-milling larger glass bubbles instead of the commonly used small glass bubbles. Glass bubbles with a median particle size of 47.9 μm were chosen as the component. After only 5 min of ball-milling, the median particle size was reduced to 9.7 μm. The solar reflectivity of paint made from glass bubbles after 5 min of ball-milling increased from 75.8 % (without ball-milling) to 95.8 %. In field tests, radiative cooling paint made from unground 47.9 μm glass bubbles was found to be 9.4 °C warmer than the ambient temperature at noon, while the paint made by 5 min of ball-milling of these glass bubbles achieved a temperature close to that of ambient air. Moreover, the price per unit of weight of 47.9 μm glass bubbles is only 40 % that of the previous 16.1 μm glass bubbles.