Multilayer assembly of phase change material and bio-based concrete: A passive envelope to improve the energy and hygrothermal performance of buildings

Abstract

Phase change materials (PCMs) can improve indoor thermal comfort and reduce energy consumption, while bio-based concrete is an environment-friendly material that enables indoor humidity regulation and heat insulation. However, only a few studies have explored the integrated application of the two materials and comprehensively analyzed the energy and hygrothermal performance. In this study, a passive envelope solution that integrates PCM and hemp concrete is proposed to improve buildings’ energy, thermal, and hygric performances simultaneously. Four integrated scenarios were considered and compared with a baseline scenario (hemp concrete only). The performance of the integrated envelope was studied numerically based on the impact of the PCM’s properties and its location in the envelope. The results highlight the indispensable role moisture transfer plays in determining the indoor hygric environment and heat load, as well as the valuable effect of the integrated envelope on improving both energy and hygrothermal performance. Scenario 4/5 (with PCM closest to the interior) in the summer showed the greatest performance improvement compared to the baseline scenario, with reductions of 8.2%, 46.3%, and 43.7% for heat load, temperature fluctuation, and partial water vapor pressure fluctuation, respectively. The impact of the PCM properties in scenario 4/5 illustrate that the optimization of the integrated envelope can be achieved by increasing the thickness and latent heat of the PCM and identifying its appropriate phase transition range. From a year-round perspective, scenario 4/5 is also notable, as it shows great potential for saving energy and adapting to climate humidity variation while guaranteeing moisture equilibrium within the hemp concrete. The three-year assessment confirmed a lack of condensation and no risk of mold growth for such an integrated envelope, as the relative humidity in key locations remains below 75%.