Bio-PCM to enhance dynamic thermal properties of dry-assembled wooden walls: Experimental results

The lightweight features of dry-assembled wooden walls make the building envelopes not suitable for significantly limiting energy demands. Natural Phase Change Materials (bio-PCM) can be used to enhance the buildings thermal mass preserving the structures sustainability. For this purpose, an experimental campaign was carried out on different configurations of wooden walls, installable both vertically and horizontally, and in which PCM can face both internal and external environments. Preliminary, transient simulations were conducted to identify the suitable PCM melting temperature and the best allocation that conciliates winter and summer needs. Successively, experimental tests allowed for thermally characterizing the wall through dynamic indices, since standardized procedures cannot be employed in the presence of PCMs. At an annual level, energy results showed that a bio-PCM with a melting temperature of 23 °C inserted in the internal side of the wooden wall is preferable, whereas PCMs on both sides produce marginal improvements. Experimentally, a single layer of bio-PCM on the inner side produced a decrement factor of 0.032 (−81%) and a time-lag increase of 2 h when compared with the base case without PCM, whereas the periodic thermal transmittance reduced from 0.148 W/m2K to 0.091 W/m2K. When bio-PCMs are allocated in both the sample sides, a further time-lag increase of 1.6 h and a limitation of the periodic thermal transmittance to 0.086 W/m2K was observed. Conversely, an increase of the decrement factor to 0.049 was detected, due to a negative interference of the PCM melting and solidification processes on the sample surface temperatures. Therefore, in these circumstances experimental data could define unreliable decrement factors for the considered envelope component.