Evaluation of the impact on energy and thermal comfort of PCM-enhanced on roof buildings in semi-arid climates

In recent decades, buildings have emerged as a significant contributor to urban energy consumption. In order to mitigate the environmental impact of this phenomenon, the utilization of thermal storage through phase change materials (PCM) in the building envelope has become an innovative strategy. Nevertheless, despite the assumption that the incorporation of PCM will improve the thermal efficiency of buildings, this is not a guaranteed outcome in all instances. In climates that exhibit pronounced seasonal extremes, the capacity of PCM for thermal storage is constrained. This experimental and numerical study, focused on semi-arid climates, aimed to enhance the performance of PCM in combination with natural ventilation thus the thermal performance of building roofs. In addition, the study extends the evaluation by combining PCM with insulating materials and reflective paint. It is anticipated that the integration of PCM with another passive strategy will enhance its thermal performance, particularly in extreme climates where the full potential of this material is often constrained. The results of the study focus on the analysis of the thermal behavior of the PCM, thermal comfort, and annual energy demand, with the environmental and cost implications that this represents. The experimental study, conducted in real climatic conditions, focused on the combination of PCM with natural ventilation. The numerical study generated 108 new scenarios, which were evaluated during a typical meteorological year. The results demonstrated that the incorporation of natural ventilation optimizes the thermal behavior of the PCM, enabling an increase in the time spent in a solid state by up to 41%. This enhances the efficiency of the complete cycle, ensuring its completion within a single day. Moreover, the utilization of PCM resulted in a reduction of the maximum peak indoor air temperature during the summer months by between 1.9% and 7.2%, while an increase in the minimum valley during the winter months was observed, ranging from 4.4% to 10.4%. The duration of time spent within the comfort zone was increased, up to a maximum of one hour during the summer months. Similarly, the introduction of natural ventilation through ducts into an air chamber with PCM has been demonstrated to reduce annual energy gains by up to 92.9%. Ultimately, the combination of PCM with reflective paint and XPS insulation has the potential to result in annual savings of up to 12.95 tCO₂e, with an estimated investment return period of 2.8 years.

https://orcid.org/0000-0003-2462-2499