Numerical study of heat transfer of a double layered PCM building roof in a semi-arid climate

The thermal performance of a concrete roof with a double phase change material (PCM) layer on the interior concrete surface under the semi-arid weather of Monterrey´s city is presented. The roof was numerically analyzed based on a computational fluid dynamic (CFD) simulation with three types of models: The base concrete case (RC), the concrete roof with one PCM layer (RC-PCMi), and the concrete roof adding a double PCM layer (RC-PCMi-PCMj). The numerical CFD simulations were conducted during the warmest, coldest and typical day of the year. The software used for the simulation was Ansys Fluent. The results indicate that the RC-PCM29 has the lowest thermal values during the warmest day reducing the indoor energy by 96.51 W/m2 representing a 7.4% reduction. In the other hand the RC-PCM25 obtained the best performance for the coldest day, reducing indoor energy by 300.29 Wh/m2 or 32.7% reduction. Furthermore, the RC-PCM29-PCM25 double PCM configuration resulted in the best thermal performance, reducing the annual energy to the indoor by 3,613.89 kWh or 26.2%. Also, considering a roof area of 36 m2 of a building located in Monterrey city, the payback period will be up to 3.45 years with an internal rate of return of 29.0%, resulting a cost-effective use of the double PCM layer. Besides the annual carbon emission savings are 1 572 04 𝑘𝑔 𝐶𝑂 2 𝑒𝑞. Therefore, it is recommended that the RC-PCM29-PCM25 will improve the thermal behavior of buildings located in Monterrey.