By Nidhi DhullMay 8 2024Reviewed by Susha Cheriyedath, M.Sc.A recent study published in Architecture evaluated the solar shading effect on sunny facades using non-intrusive infrared (IR) thermography during both the summers and winters. This experimental evaluation of solar protections on opaque surfaces involved monitoring both sunny and shaded areas of a social housing building in Zaragoza, Spain.
Photographic image, IR thermography and temperature gradient (from top to bottom), in summer. L1, L2 and L3 indicate different readings along the façade (see IR thermography image). The red lines show the placement of the louvres. Image Credit: https://www.mdpi.com/2673-8945/4/2/14
Background
As temperatures continue to rise due to global warming and the urban heat island effect, there's an increasing need to enhance the solar protection of buildings during summer while still maximizing solar gains in winter.
Solar shading plays a crucial role in optimizing the performance of building envelopes, especially in warm regions with high solar irradiation. Beyond shielding windows from intense sunlight, it also provides protection for opaque external walls, effectively reducing energy consumption for cooling.
The concept of sol-air temperature is widely used to examine the energy efficiency of green and ventilated facade systems. However, the solar control for the opaque construction systems used in facades is rarely investigated using real measurements. Alternatively, non-destructive IR thermography has gained significant attention in controlling and assessing the thermal performance of energy efficiency approaches implemented in the construction sector.
Methods
The study focused on a demonstrator building utilized for the LIFE 10 ENV/ES 439 project, a social housing building located in Zaragoza. A south-facing facade was selected for thermal analysis due to its significant solar exposure and adjacency to a large inner courtyard, which helped mitigate slope errors in the IR measurements.
To retrofit the building's envelope, an external thermal insulation composite system (ETICS) was employed, comprising a 50 mm polystyrene insulation and cement render with a light ochre-colored finish. Additionally, a 1.15-meter continuous overhang made of aluminum louvers was installed to regulate solar radiation, permitting sunlight entry during winter while blocking it during summer.
Throughout the year 2015, an IR camera monitored temperatures in both shaded and sunny areas of the facade during summers and winters. Concurrently, a hygrothermal monitoring system equipped with a weather station and data logger captured relative humidity, temperature, and wind speed within the building.
Using the recorded measurements and climate data obtained from the State Meteorology Agency of Spain (AEMET) at the city's airport, researchers calculated sol-air temperatures. Instead of relying on conventional sol-air temperatures, they utilized temperatures derived from IR thermography to theoretically assess the impact of solar protection on heat flux through the building envelope under steady-state conditions.
Study Results
The strategy employed for solar protection on the building under consideration significantly influenced the facade’s thermal response. It resulted in a temperature difference of 7.4 °C in summer and up to 1.2 °C in wintertime between the sunny and shaded areas.
In the summertime, the shading system protected the building from incoming solar radiation through the windows and heat transfer through the wall by reducing its heat gains. However, the limited convective airflow prevents the cooling of walls and reduces inward heat fluxes when the outdoor temperature is lower than the indoor one. Thus, mobile solar protection systems should be considered to allow moderate surface cooling at dusk.
In winter, the horizontal solar protections reduced the convective air flow and air locked under them, increasing the temperature under the louvers as compared to the open areas of the facade. This warm bubble of entrapped air reduces heat fluxes and diminishes indoor-outdoor temperature differences. Consequently, indoor temperatures become more stable, which is favorable for mitigating fuel demand for indoor heating systems.
The comparative analysis using temperature data from air, sol-air, and actual surface to estimate heat fluxes revealed a significant gap. The former two resulted in high inaccuracy and overestimation of the performance of the buildings in comparison to the actual behavior. This is due to the higher influence of air temperature than of solar radiation on the determination of sol-air temperature. Alternatively, IR thermography proved to be a reliable technique for verifying the shading solutions’ performance.
Conclusion
Overall, the solar shading system implemented in this case study helped decrease surface temperature in summertime and convective airflow in wintertime. Its performance was enhanced by the prevalence of dense shadows from non-reflective materials in louvers. Additionally, the use of clear colors reinforced surface homogeneity in winter and decreased solar absorptance in summer.
The steady-state calculations demonstrate that shadowing can reduce thermal losses by up to 30 % on winter nights and 50-60 % on summer days. This analysis, considering a unidirectional flux, has limitations in climates with high thermal oscillation of temperatures. However, it allows a simple comparison among different shading solutions.
The inconsistencies in simulation results from different data sources can be overcome by revising the conventional external surface resistance values according to specific climatic conditions such as wind protection, sun irradiation, urban materials, etc.
In conclusion, the use of thermography in this study helped analyze the shadowing impact of ETICS as well as the urban layout on the thermal performance of the building. The authors aim to extend its usage in several situations over the years and complement it with real climate data for simulating building performance.
Journal Reference
Barbero-Barrera, M. del M., Tendero-Caballero, R., & García de Viedma-Santoro, M. (2024). Impact of Solar Shading on Façades’ Surface Temperatures under Summer and Winter Conditions by IR Thermography. Architecture, 4(2), 221–246. https://doi.org/10.3390/architecture4020014, https://www.mdpi.com/2673-8945/4/2/14
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