Assessment of the Impact of Cool Roofs in Temperate Climates through a Comparative Experimental Campaign in Outdoor Test Cells

Over the last few decades many bibliographical studies have been conducted on cool roofs, by analyzing both the energy performance during summer and winter seasons and their contribution in mitigating the urban heat island effect. This paper describes the experimentation carried out in three outdoor test cells to comparatively assess the behavior of a cool roof solution with respect to a ventilated-roof and a warm-roof. The monitored data have confirmed that in summer cool roofs are the best solution, with respect to traditional tile roofing, sensibly reducing surface temperatures as a function of the solar direct radiation level (15-25 °C for I > 600 W/m2 and 5-15 °C for I < 300 W/m2, independently of the season). Furthermore, cool roofs involve an energy saving related to summer cooling by about 20% as to a warm-roof and 15%-20% as to a vented-roof. During winter, cool roofs improve the heating energy performance of a vented-roof by about 12%, against a slightly increased consumption (<5%) if compared to a warm-roof. These data confirm that, in temperate climates, cool roofs are appropriate solutions to sensibly improve summer energy performances with a negligible negative impact during winter, and to positively contribute to the mitigation of the heat island effect.