Inclusion of microencapsulated phase change materials in waterborne paints to enhance radiative cooling performance

Abstract

Radiative cooling materials are a promising technology for reducing energy demand for thermal control in buildings and surfaces. Paint formats are versatile and relatively inexpensive implementations of this technology. Waterborne polyurethane paints are environmentally friendly coating systems that possess high abrasion resistance and durability. However, the implementation of radiative cooling in polyurethane paints is limited due to their less favorable optical properties. In this work, the addition of phase change materials (PCM) to the paint formulation to enhance cooling performance is investigated. Capric acid, encapsulated in silicon dioxide particles via a sol–gel process, was selected as the PCM, and barium sulfate particles were used as paint pigments. At a fixed total particle volume concentration, the incorporation of PCM increases the effective heat capacities of paints. However, the solar reflectance decreases as the PCM volume concentration increases, especially above 0.25. An outdoor test reveals that the inclusion of the PCM reduces the heat load in the paint and consequently enables sub-ambient cooling. This study suggests that the PCM components can enhance the cooling performance of radiative cooling paint systems that struggle to achieve sub-ambient cooling.