The spatial evaluation of the radiative human body heat exchanges: An effective contribution for limiting energy consumption and achieving better indoor conditions in buildings

Radiative heat exchanges inside buildings remarkably affect the thermal balance of the human body in confined spaces and the related thermal comfort sensations of people. The mean radiant temperature is an important component of this balance. Unfortunately, it is usually computed by means of too simplified relationships, which significantly influence the comfort evaluations. Such simplified approaches are also accountable for a less effective design of HVAC systems which, in turn, could result in high energy consumption in the climatization of buildings. However, an accurate evaluation of the mean radiant temperature, especially when high intensity sources are present in a given internal space, depends on the angle factors between human subjects and surrounding surfaces of the enclosure. Angle factors, in turn, are direct functions of the projected area factors of the human body. Presently, there is still a certain lack in the availability of simple and reliable methods for computing angle factors of people in assigned postures, particularly in case of complex geometry and presence of heat high intensity sources, like sun. A comprehensive method is here introduced for evaluating the thermal comfort conditions of indoor spaces, avoiding the difficult singling out of several algorithms, dispersed in an inorganic way in the literature. A further contribution consists in the possibility of evaluating geometrically complex enclosures also in presence of direct solar radiation entering the room. Moreover, an analytical method for computing the projected area factors, based on experimental results, obtained by means of a photographic apparatus on purpose designed, is included in the methodology. An application of the method to a typical building situation in presence of direct solar radiation is also proposed.