Influence of quasi-steady thermal regime on the thermophysical properties of thermal insulation materials

The thermophysical properties of two types of thermal insulation materials - mineral wool and extruded polystyrene foam - were investigated under steady-state and quasi-steady thermal regimes. The actual values of the thermophysical characteristics of the materials were determined and compared with regulatory data to assess their effectiveness in construction applications. Both laboratory and theoretical studies were conducted. A discrepancy was found between the thermal conductivity coefficients obtained from testing wall fragment samples and those determined theoretically. The study provides a rationale for the inaccuracy of the conversion values for thermal conductivity from dry to design conditions as presented in regulatory documents. The deviation in the thermal conductivity coefficient was 44% for mineral wool and 19% for extruded polystyrene foam. A high degree of agreement was established between the planar calculation model and laboratory results for both types of insulation under steady-state and quasi-steady thermal regimes, allowing for the verification of the calculation model. Theoretical studies examined both planar structural systems and enclosing structures with geometric thermal bridges. It was found that, in constructions using extruded polystyrene foam, more stable temperature values were observed over time within the thickness of a structure simulating a building corner, compared to a similar structure insulated with mineral wool. This stability can reduce the number of zero-crossing cycles for load-bearing structures located within the enclosure, which has a positive effect on their durability and reliability.