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The effects of climate change on the built environment represents an important research challenge. Today, green roofs (GRs) represent a viable solution for enhancing energy and urban resilience in the face of climate change, as they can have a positive impact on the building's indoor thermal comfort and energy demand, as well as inducing various environmental benefits (easing urban heat island effects, improving the management of runoff water, reducing air pollution, etc.). Thus, it is important to be able to assess their effectiveness, both today and under future climate conditions, in order to evaluate whether they can also provide a valid long-term solution. In this paper, a simulation approach is proposed to evaluate the energy and indoor-comfort efficacy of GRs installed on a cluster of buildings with respect to climate change and demographic growth. To illustrate the proposed methodology, it has been applied to two European urban environments characterized by very different climatic conditions (Esch-sur-Alzette in Luxembourg and Palermo in Italy) considering their behaviour over a period of 60 years (2020, 2050, 2080). Results showed that, with respect to standard existing roofs (i.e., without the presence of green coverage), and considering the rising temperatures due to climate change, during cooling seasons GRs enabled significant energy savings (ranging from 20% to 50% for Esch-sur-Alzette and from 3% to 15% for Palermo), improvement of the indoor comfort (reduction of the average predicted mean votes − PMVs) and attenuation of the ceiling temperatures (2–5 °C for both contexts) of the buildings' top floors.

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.