The methods for creating building energy efficient cool black coatings

• The coatings colored with chromite iron and manganese ferrite are not cool coatings.
• The black coatings colored with perylene black are qualified cool coatings.
• The black coatings colored with dioxazine purple are real cool coatings.
• Adding yellow pigments to a purplish black coating forms a true black color.
• The use of the cool black coatings can save cooling energy consumption in summer.

The optical and thermal properties of black coatings pigmented with different black colorants were systematically investigated, and their surface temperature reduction values and cooling energy savings were estimated relative to the black coating pigmented with carbon black in Shanghai, China. The black coatings separately pigmented with NIR-transmitting perylene black and dioxazine purple colorants were identified to be real cool black coatings. The addition of chrome titanium yellow to the black coating pigmented with dioxazine purple re-establishes the true black coatings. Over white basecoats, the estimated surface temperature reduction values and annual cooling energy savings in Shanghai are 13.8 °C and 3.9 kW h m−2 yr−1, respectively, for the black coating pigmented with perylene black colorant; these two values are 10.2 °C and 2.24 kW h m−2 yr−1, respectively, for the black coating pigmented with dioxazine purple colorant.