A Dimensionless Study Describing Heat Exchange through a Building’s Opaque Envelope

The urban environment represents one of the main contexts in which natural resources are exploited to support intensive human activities, especially from an energy perspective. In this context, there is still a lack of general methodologies/tools which can be used to understand the behavior of buildings and to prove their sustainability under real operating conditions, depending on their location, construction characteristics and materials, plants, external conditions, and conduction. In this research, the Buckingham theorem is applied to the thermophysics of buildings, describing the heat transfer of opaque surfaces in a transient regime. The abstraction of dimensionless numbers merges the main phenomena of interest, such as thermal conduction, convection, and radiation, enhanced by consideration of the surface sun–air temperature and the external air temperature. The parameters themselves were mutually matched through a proper equation, whose coefficients were determined by a regression analysis of the measurements from an intensive experimental campaign investigating a building in Florence for 3 years. The resulting correlation shows a good agreement with the available dataset and a determination coefficient of over 70%. Therefore, the proposed approach, owing to the generalization of the dimensionless numbers, suggests the possibility of sustainability estimates, from an energy point of view, of envelope/plant/user systems, including assessments at a higher scale than that of a single building.