Energy Efficient Building's Envelopes. Numerical and experimental analysis of innovative solutions

The aim of this study is to set up a simplified and validated numerical platform to describe several technologies concerning the energy performance improvements of glazed and opaque building envelopes. The study included the validation of DIGITHON, a detailed simulation software and the development of a simplified transient numerical model in respect of glazed buildings. DIGITHON, was validated against experimental data, and then a parametric study was carried out through it to evaluate the air pre-heat efficiency of implementing the façade as an energy recovery unit. The simplified model was dedicated to the thermal engineering designers dealing with projects preliminary phases .The simplified model was validated against experimental data. Later an extensive comparison between the detailed software DIGITHON and the simplified model was carried out for different climatic conditions to evaluate the influence of considering indoor zones thermal inertia. Although the simplified model estimates thermal loads higher than DIGITHON, nevertheless this can be considered a beneficial design safety aspect as long as it is implemented in the preliminary design phases. Later an innovative locating of photovoltaic modules at building glazed facades was investigated through the commercial software TRNSYS. The methodology of modelling double skin-glazed façades combined with different strategies of ventilation applying TRNflow software was thoroughly clarified. The results show a reduction in thermal heating loads compared to conventional location of PV on external building surfaces. On the other hand the cooling loads are increased, hence to improve the performance of the system in summer hot season, the technology of phase changing material (PCM) was tackled in the research as a latent thermal storage system. A numerical investigation of the effect of PCM in building sector, solely and combined with PV modules to improve its thermal performance, has been carried out. Two numerical models (equivalent capacitance and enthalpy linearization methods) describing the PCM thermal and optical performance have been developed and validated. Results show that thermal loads reductions of a system implementing PV/PCM modules reach 30% in summer season. Afterwards, the research through experimental campaign and numerical heat transfer modelling optimised the selection and location of two technologies within a residential roof attic: the technologies considered were PCM modules and reflective surfaces; five transient numerical models have been developed and validated. The results clarify the influence of the proper selection for melting-solidification PCM range suiting each application in order to reach optimum specific heat capacity values which could improve the overall thermal balance of the inner zone. Finally, computational fluid dynamics CFD models have been applied to different case studies to describe the thermal performance of vertical glazed envelopes.

Lo scopo di questo studio è sviluppare e validare una piattaforma numerica semplificata per descrivere diverse tecnologie riguardanti i miglioramenti di prestazione energetica dell'involucro edilizio costituito da parti vetrate e opache. Lo studio comprende lo sviluppo e la validazione di due modelli numerici transitori in materia di edifici vetrati. Successivamente un software commerciale, TRNSYS, è stato applicato per indagare una modalità innovativa di integrazione di moduli fotovoltaici nell'involucro edilizio. Un altro tema promettente, affrontato in questa ricerca, è l'indagine numerica sui materiali con cambiamento di fase (PCM) nel settore delle costruzioni, da soli ed in combinazione con moduli fotovoltaici per migliorarne le prestazioni. Due modelli numerici (metodo della capacità equivalente e metodo della linearizzazione dell'entalpia) che descrivono le prestazioni termiche e ottiche dei PCM sono stati sviluppati e validati. Un'analisi sperimentale e numerica ha permesso di ottimizzare la selezione e la posizione di due tecnologie, moduli PCM e superfici riflettenti, nel sottotetto di un edificio residenziale. Cinque modelli numerici transitori sono stati sviluppati e validati a tal fine. Infine, modelli di fluidodinamica computazionale (CFD) sono stati applicati per descrivere le prestazioni termiche delle chiusure vetrate e analizzarle attraverso diversi casi di studio.