Optical properties across the solar spectrum and indoor thermal performance of cool white coatings for building energy efficiency

• Two waterborne cool white coatings for building energy efficiency were prepared.
• The solar reflectance of cool coatings S1 and S2 is respective 0.879 and 0.892.
• The predicted industrial limits for practical reflective cool white coatings are 0.91.
• The coatings integrate multiple cooling principles and show super cooling effect.
• Radiant heat flux may be significantly reduced by use of cool white coatings.

Two single-layer, waterborne cool white coatings for building envelopes were recently developed for use in improving building energy efficiency. After the coatings were manufactured, their optical properties over the solar spectrum and their indoor temperature reduction effect were systematically investigated using appropriate tools, and the advantages/disadvantages of single layer cool white coatings over multilayer ones were discussed in detail. The preparation process enables these two coatings to integrate multiple cooling principles and thereby exhibit high solar heat reflectance and good indoor temperature reduction. The predicted industrial limit of solar heat reflectance for practical reflective cool white coatings is 0.91. Use of cool white coatings significantly reduces radiant heat flux. The temperature reduction effects evaluated by a self-developed device cannot describe adequately the indoor cooling performance of cool coatings.