Influence of external surface colour on the periodic heat flow through a flat solid roof with variable thermal resistance

Abstract

In this research, the influence of external colour on the dynamics of the heat flow through a flat solid roof, with variable thermal resistance, has been studied analytically. The chromatic effect on the density of heat flow through the roof has been analysed using periodic solutions of the heat conduction equation, by means of Fourier analysis. The simulation has been carried out over a period of 24 h, for the summer design day of Campinas, in the State of São Paulo, Brazil, and its composite climate. An almost linear relationship between heat flow amplitudes (Δqi) and the thickness of a concrete roof has been noticeable in the range from 5 to 14 cm for a grey coloured exterior surface and a corresponding white one. Conversely, from 15 cm and more, this relationship starts flattening. It may be concluded that as the thermal resistance of the concrete roof increases (>15 cm), the effect of the exterior colour surface on the periodic heat transfer through the roof is attenuated. As a consequence, the conflict between choosing colour for aesthetics and assuring energy efficiency of opaque building components in hot climates can be mitigated, if building designers make proper use of thermal inertia. Copyright © 2003 John Wiley & Sons, Ltd.