PSI - Issue 55

Andréa R. Souza et al. / Procedia Structural Integrity 55 (2024) 143–150 Andrea R. Souza et al / Structural Integrity Procedia 00 (2019) 000–000

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The retrofit of roofs can reduce summer peak temperatures by 7%, irrespective of the R-value, when comparing the aged (agedR1/R2) condition with the retrofit (resR1/R2). However, when considering the Csa climate zone, as depicted in the annual distribution of the maximum ST (Fig. 4b), the influence of the R-value is nearly insignificant (1%) during the winter season, while reflectance maintains its reduction effect (6%). Similar to the roof application, the west façade is exposed to higher ST in the Csa zone in summer. Retrofitting the west façade reduces peak summer temperatures by 4%, regardless of R-value, when comparing the aged condition (agedR1/R2) with the retrofit (resR1/R2). However, as can be seen from the annual distribution of maximum ST in Fig. 5 the influence of the R-value during the winter season in climate zone Csa is almost negligible (2 %), while reflection continues to have a reducing effect (4 %). The numerical results are similar to Souza et al. (2023) for Portuguese simulations that the reduced ST for the city of Porto (Csb climate) achieved 3% when using NIR black coatings. Therefore, Fig. 6 present the correlation between the reflectance and the maximum surface temperature for the two configurations of R-value.

Fig. 6 Correlations between reflectance and maximum surface temperature for Csa zone: (a) Horizontal orientation; (b) Vertical west orientation.

As expected, the reduction of the surface reflectance due to the reflectance increment is more effective in the roof (Fig. 6a) than in the west façade (Fig. 6b) as verify in Alonso et al. (2017) and Dias et al. (2014). This effectiveness is related to the higher absolute value of surface temperature result from the solar irradiation, although is worth highlighting that the in both cases, the increment on R-value reduces the influence of the reflectance. 4. Conclusions The study highlights the promising potential of NIR black paints as a cost-effective retrofit solution for Portuguese buildings. The effectiveness of these paints depends on several factors, such as the climate zone and the orientation of the building envelope. The results show the expected thermal behaviour of the NIR reflective materials on the experimental campaign and the numerical simulation for the surface temperature, where the NIR paint could be used as a quick retrofit method, listing: • The NIR dark paints can reduce the surface temperature and the cooling/heating demand of Portuguese buildings. • The use of NIR dark paints on roofs could be more effective than on façades due to the radiant energy received. • There is an optimal design value between the U-value and the reflectance. In addition, it is worth noting that using black NIR paints impacts surface temperatures in both summer and winter. Therefore, further assessment of the risk of condensation on building facades in different climates is needed. Comprehensive assessments should also be carried out to quantify the reduction in cooling and heating degree-days through energy simulations. These considerations will help us better understand the practical implications and long term benefits of using NIR black paints as part of a building's energy retrofit strategy.

Acknowledgements

This research was financially supported by: Base Funding – UIDB/04708/2020 of the CONSTRUCT – Instituto de I&D em Estruturas e Construções - funded by national funds through the FCT/MCTES (PIDDAC). A. R. would like to acknowledge the