Design considerations toward the effective use of thermal mass distribution inside a space need to be supported by optimization decisions in order to adequately control the indoor thermal environment through the charging and discharging of heat. In naturally heated or cooled spaces, the thermal performance of internal mass is affected by the interior solar dynamics and the mass distribution layout within the space envelope. The placement with regard to solar exposure, the size, and the thermophysical properties are all aspects of thermal mass that must be evaluated in their contribution to the resulting profile of the inside air temperature. Among these parameters, the solar impact on the interior surfaces is the most elusive because of daily variations in solar exposure of the interior surfaces. The direct and diffuse components of solar radiation that enter a space have been commonly treated as if they were both diffuse. Such an assumption dismisses a significant aspect of the real solar impact on the space, which leads to inadequate placement of internal mass. Above all, this assumption does not comply with the understanding of solar transmission through glass. This paper presents a more precise mathematical model of the thermal impact that each of these two radiation components has on the indoor thermal mass by considering the dynamics as a result of the sun's motion across the sky, the changing geometry and areas of the sunlit configurations cast along the room's interior surfaces, and the shifting location of these internal sunlit areas. In addition, this paper provides a comparative analysis of the results obtained from a physical experiment and from a simulation.

AUTHOR: Tahar Messadi, Arch.D.
CITATION: Thermal Performance of the Exterior Envelopes of Buildings VII
KEYWORDS: December, Florida, 1998
YEAR: 1998