Hygrothermal performance of an innovative resource efficient composite masonry unit with embedded biobased insulation

Abstract

The REcycled Stone and Concrete Unit (RESCIU) is an exemplary case study of load-bearing composite masonry units (cMU) based on a unique and registered design that involves sandwiching a 12 mm S-shaped biobased polyurethane foam (BPUF) between C-shaped recycled solid elements, one in Globigerina limestone and the other in concrete. Thermophysical and hygric material properties were measured under strict laboratory conditions and their related error analysis was calculated. To complement this, a locally recorded hourly weather file for Malta (representative location of Mediterranean climate) was used to implement boundary conditions for both 1D and 3D hygrothermal simulations. The measurement of U-value on RESCIU prototypes via hotbox apparatus converged to (averaged) 1.39 ± 0.19 W/(m2K). The 3D simulation, validated in a precedent publication, aligned closely with hotbox results yielding an URESCIU of 1.40 W/(m2K). 1D assessments with 20 mm of the S-shaped cavity led to a reduction of theoretical thermal transmittance of up to 0.71 W/(m2K) and a prolonged thermal lag up of up to eleven hours (UNI EN ISO 13786). In 3D this value is slightly lower with URESCIU of 0.65 W/(m2K). However, periodic thermal transmittance YieRESCIU of 0.29 W/(m2K) in 1D mode was found overestimated compared to 0.43 W/(m2K) obtained in 3D, while the thermal lag is accurate (9 h in 3D and 9.7 in 1D). 1D hygrothermal steady state assessments (UNI EN ISO 13788) reported neither the risk of developing surface mold (1D only) nor interstitial condensation (Glaser method), the latter calculated in both 1D and 3D mode for June (summer condition) and December (winter condition). In June 1D and 3D simulations results are very similar as opposed to higher discrepancies detected in December, with 1D simulation consistently underestimating DBT, RH, pe for the vertical sections characterized by one layer of insulation. This confirms the RESCIU block is suitable for applications in Mediterranean climate.