Microclimate on building envelopes: insulating with geometry
About 40 percent of the world’s energy consumption is accounted for by buildings alone, which could be considerably reduced through proper thermal insulation of the building envelope. Thermal insulation in buildings is traditionally achieved by stacking layers of insulating materials, thereby creating a laminated orthogonal façade. However, effective thermal insulation can also be achieved through additional methods. For example, unique envelope geometries in nature are used by desert succulents and arctic animals to survive in harsh climatic conditions. Nature’s approach to insulation demonstrates that thermal performance is affected not only by the material itself, but also by the organization of the material in the given space.
Contemporary tools and technologies used by architects have made the design and fabrication of complex geometries achievable. In turn, the availability of these design and fabrication tools has led to an increasing interest in the use of complex geometries in architecture.
Studies have demonstrated the impact of geometries on changes to the airflow that in turn improve thermal performance, from micro-level of building façade surfaces to the macro-level of a city. Large-scale studies showed that air movement within the city depends on morphology, street design, orientation, and form. Examining the shape of domed roofs in Persian deserts revealed their ability to create higher air velocities above the vaulted section, thereby enhancing heat transfer and maintaining the thermal comfortability of the interior spaces.
In this research hypothesized that changing the geometry of a flat smooth façade tile can shape air patterns on the surface. In turn, these patterns could then potentially thicken the boundary layer, resulting in improved insulation of the surfaces.
The goal of this research is to develop a methodology and a database for creating new energy-efficient types of building enclosures and for evaluating their thermal performance. We chose to use concrete tiles in the study as they have been found to encompass the potential of basic shape cavities that improve thermal resistance.
Several groups of sculptured tiles were developed, using a systematic approach (i.e., repetition of basic geometries), biomimicry, and inspiration from natural envelopes. Air flow behavior and heat transfer rates were examined at three different wind speeds, through both experiments and computational fluid dynamics simulations using a configuration of flow impingement that can be regarded as the worst case scenario. After successfully validating the data, additional numerical simulations were conducted for all developed tiles using the Star-CCM+ commercial software. The results showed an improvement in the insulation performance of about half of all the tested cases.
Moreover, significant improvements were seen in the geometries that mimicked animal fur, achieving heat transfer rates that were up to 24% lower than those achieved by smooth tiles. Our results indicate that the application of such tiles with increased thermal resistance could save on thermal insulation materials and improve the thermal performance of building façades.
Funding:
The project is sponsored by the Israeli Ministry of Construction and Housing (~100,200US$).
The project is a collaboration with:
Prof. Rene van Hoet. The faculty of Mechanical Engineering. Technion
Dr. Yosie Elimelech, The faculty of Aerospace Engineering, Technion
Scientific papers that were published on this research:
Grobman, Y.J., Elimelech, Y. Microclimate on building envelopes: testing geometry manipulations as an approach for increasing building envelopes’ thermal performance. Architectural Science Review, 59:4, 269-278. 2015. DOI: 10.1080/00038628.2015.1025688.
Hershkovich, C. Van Hout, R. Rinsky, V. Laufer, M. Grobman Y. J. “Microclimate on building envelopes: wind tunnel and computational fluid dynamic analysis of basic and complex geometries”. SimAUD 2017 conference proceedings. May 22-24, 2017. Toronto. Canada.
Van Hout, R. Rinsky, V. Grobman, Y.J., Experimental Study of a Round Jet Impinging on a Flat Surface: Flow Field and Vortex Characteristics in the Wall Jet. International Journal of Heat and Fluid Flow. DOI: 10.1016/j.ijheatfluidflow.2018.01.010.
Van Hout, R. Rinsky, V. Hershkovich, C., Grobman, Y.J., Outer shear layer characteristics of a radially expanding wall jet on smooth and dimpled surfaces. International Journal of Heat and Fluid Flow. Volume 72, August 2018, 304-316. 2018. DOI: 10.1016/j.ijheatfluidflow.2018.06.011.
Van Hout, R. Rinsky, V. Sasson N., Hershkovich, C., Moshe Tshuva, Grobman, Y.J. Axisymmetric jet impingement on a dimpled surface: Effect of impingement location on flow field characteristics. International Journal of Heat and Fluid Flow. 17th September 2018. DOI: 10.1016/j.ijheatfluidflow.2018.09.010.
Pushkar, S. Yezioro, H. A. Hershcovich, C, Grobman, Y.J. Life-cycle Assessment of Sculptured Tiles for Building Envelopes in Mediterranean Climate. Buildings 12(2), 165. 2022. DOI: 10.3390/buildings12020165
Grobman, Y. J, Hershkovich, C., Balsan, A., Blonder, A., Austern, G., Weizmann, M., Perlstein, Y., Developing building envelope cladding tiles based on complex geometry – final report for grant #2022402. Submitted to the Israeli Ministry of Construction and Housing. 6.2018 (In Hebrew).
Hershkovich, C. Van Hout, R. Rinsky, V. Laufer, M. Grobman Y. J. Thermal performance of sculptured tiles for building envelopes. Building and Environment. April 2021. DOI: 10.1016/j.buildenv.2021.107809.