Modelling Indoor Radiative Heath Exchanges for Effective People Thermal Comfort and HVAC Design

Radiative heat exchanges inside buildings are responsible of a relevant part of the thermal balance of people occupying such confined spaces and, in turn, of their thermal comfort sensations. Mean radiant temperature of the internal surfaces is supposed to affect considerably this balance but, usually, it is computed by means of too simplified relationships that significantly affect the comfort evaluations. These simplified approaches can be also accountable of a less effective design of HVAC systems. Unfortunately, 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, on the other hand, are a direct function of the projected area factors. Presently, there is still a certain lack in the availability of simple and reliable methods capable of computing angle factors of people in assigned postures, particularly for buildings characterized by a complex geometry. On the base of experimental results, obtained by means of a photographic apparatus on purpose designed, a comprehensive algorithm is presented for assessing angle factors of people living or working in confined spaces, where heat high intensity sources are present, and sun among them. The algorithm, that is applicable to people in seated or standing postures, apart a more accurate evaluation of the indoor thermal comfort of people, allows a more effective design of heating, ventilating and air conditioning mechanical systems.