| Summary: | The current study experimentally investigates the optimal thickness of a phase change material (PCM) layer incorporated composite roof under severe exterior temperatures. Three PCM thicknesses, namely 10, 15 and 20 mm, are embedded inside a popular roof combination for residential buildings in Iraq compared with the reference roof without PCM. The composite roof is composed of Isogam (4 mm) as a roofing material, concrete (50 mm) as a main roof layer, and gypsum board (8 mm) as a cladding layer, which is the worst thermal-performed roof combination in the country. Each PCM thickness case's thermal performance has been evaluated considering energetic indicators based on room temperature, interior surface temperature, and average outside surface temperature. These indicators are room maximum temperature reduction (RMTR), average temperature fluctuation reduction (ATFR), decrement factor (DF) and time lag (TL). The experimental results showed that the room temperature could be reduced by up to 9 °C compared with the reference roof. Moreover, the best thermal performance is reported for the composite roof based 20 mm thickness which resulted in a maximum of 13.9 % 10.74 °C, 44.7 % and 190 min of respectively RMTR, ATFR, DF and TL more than that of the reference case. The study concluded that the thicker PCM layer results in better thermal performance. However, increasing PCM thickness from 10 to 15 mm and then to 20 mm reduced RMTR by 2.3 % and 0.4 %, respectively. Therefore, the effect of PCM heat discharging medium and the economic concern should be considered when installing large PCM thickness/quantity into real scale buildings.
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