The Double C Block project : hot box studies deploying heat flux method inside the hot box apparatus to enhance the measurement of the block’s thermal transmittance

Abstract

The Double C-Block (DCB) is an innovative Concrete Masonry Unit (CMU) with embedded insulation developed to provide, through its geometry, both thermal and acoustic performance, apart from its established load bearing capacity. The DCB is a proven faster construction process as it eliminates the need for external/internal insulation cladding. The first load-bearing prototype developed at the University of Malta was made of two concrete C-shaped skins bonded with sprayed polyurethane foam (PUF) as the insulation layer. Earlier studies through full-scale in-situ test cells reported thermal transmittance value UDCB of 1.47 W/m2K, already outperforming the local building energy code. When running steady-state simulations Finite Element Method (FEM), results persistently showed a difference in U-values, when compared to field studies. The methodology was therefore revisited to combine these field studies with hot-box apparatus as well as performing a new set of steady-state FEM simulations by using experimental values of concrete and PUF’s thermal conductivity (TC). The latest U-value is now proven to be 1.40 W/(m2K) thanks to the use of Heat Flux Method (HFM) inside a hot box apparatus. This brings the performance gap down from 51% to a more precise 11%. This establishes the DCB as an alternative to the standard hollow core blocks plus insulation cladding. These results now push it up the technology readiness levels scale(TRL), from TRL4 to TRL6, thus lined up for commercial production.