Super Insulating Materials for energy efficient buildings: thermal performance and experimental uncertainty

In a global energy-saving policy, Super Insulating Materials (SIMs) represent an effective solution, especially in a world almost saturated with old buildings for which energy refurbishments are needed. Given their extremely low thermal conductivity, they allow reaching an excellent insulation level, with reduced thicknesses. Anyway, they are recent materials or at least recent insulation solutions for the building sector. And as all the new technologies, they bring with them some critical issues to be solved. For example, what is the accuracy of their available thermal conductivity, what are the criteria for their optimal laboratory characterisation, what are their actual thermal performances in situ and how long is their durability and what is their practical convenience still remain open questions. The aim of this research was to provide an answer to these questions, although sometimes in a preliminary way. Therefore, the thermal properties of SIMs (and in particular of the Vacuum Insulation Panels, since, between the SIMs they are the most performing and the most critical solution) were explored at different levels, from the material/panel scale to the building scale. SIMs are actually laboratory tested using traditional experimental apparatuses, such as the Heat Flow Meter (HFM) and the Guarded Hot Plate (GHP), and in accordance with as traditional standard, developed for the most common insulating material. Indeed, at the first stage of this research, the applicability of the current methodologies was extensively verified, with an in-depth analysis of the obtainable measurement uncertainties. The uncertainty assessment was performed in three different ways, to analyse the various scenarios that may occur: a theoretical standard based uncertainty evaluation, and both the Type A and Type B experimental uncertainty assessment. Once defined the best criteria for a proper evaluation of the SIMs thermal properties, they were experimentally characterised, considering the different parameters which could have some effects on their thermal behaviour (different thicknesses, average testing temperature, temperature difference, ageing conditions and so on). In practical applications of the VIPs, they must be assembled one to each other: innovatively, both the HFM and GHP apparatuses were also used for the evaluation of the linear thermal transmittance of the thermal bridges that occur in case of VIPs assemblies. The investigation performed at the material/panel level were then repeated at the component scale, to evaluate the variability and the measurement uncertainty of the linear thermal transmittance. The so defined thermal performances represented a reliable pool of input data for the dynamic hygrothermal simulations at the building scale. The goals were the evaluation of the energy efficiency of building insulated with SIMs and the prediction of the durability of these materials (considering different severities of the building envelope component boundary conditions). The outputs of the numerical simulations were then coupled with an economic analysis, to evaluate the convenience of VIP insulation, in terms of discounted pay-back period.