A Methodology Based on Equivalent Models for Multilayer Walls for the Energy Retrofit of Existing Buildings

The energy performance of building elements is typically assessed using thermal resistance that depends on the detailed knowledge of the wall assembly. Unfortunately, such information is often unavailable, as technical data may have been lost over time, and aging or weathering processes can alter the thermal behavior of building envelopes. This issue is especially relevant for the Italian building heritage. To address the lack of information, equivalent models for multilayer walls were developed to replicate the thermal behavior of actual structures. These equivalent configurations enable the evaluation of energy efficiency improvements while over coming data limitations. This paper presents a case-study focused on the development of a methodological procedure for identifying equivalent thermo-physical properties of walls in the context of an energy retrofit intervention on a listed heritage building. Numerical simulations were conducted using COMSOL Multiphysics and equiva lent configurations were tested to assess their ability to replicate the thermal behavior of the original multilayer structures. To ensure a robust validation of the proposed methodology, numerical results were compared with measurements taken in two distinct scenarios: the first prior to retrofitting, and the second after the application of thermal insulation. The results demonstrate that equivalent wall models can provide a satisfactory representation of the thermal behavior of both uninsulated and insulated multilayer walls, offering a practical approach for thermal performance assessment in scenarios where detailed stratigraphic information is unavailable.