Journal of Physics: Conference Series PAPER • OPEN ACCESS Development and evaluation of highly thermally insulating aerogel glass bricks To cite this article: Michal Ganobjak et al 2023 J. Phys.: Conf. Ser. 2600 112015 View the article online for updates and enhancements. This content was downloaded from IP address 152.88.0.137 on 04/12/2023 at 08:52 CISBAT 2023 Journal of Physics: Conference Series IOP Publishing 2600 (2023) 112015 doi:10.1088/1742-6596/2600/11/112015 Development and evaluation of highly thermally insulating aerogel glass bricks Michal Ganobjak 1,*, Wim J. Malfait 1, Janis Just 2, Marcel Käppeli2, Francisco Mancebo 1, Samuel Brunner 1, Jannis Wernery 1 1 Laboratory for Building Energy Materials and Components, Empa, Swiss Federal Laboratory for Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland 2 Laboratory for Concrete and Asphalt, Empa, Swiss Federal Laboratory for Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland * Corresponding author: michal.ganobjak@empa.ch Abstract. Since we increasingly spend time indoors, natural light inside of interiors becomes more and more important for visual comfort and overall human health through setting of circadian rhythm, and can additionally help with energy savings. Aerogel glass bricks are a new building component for perimeter walls, combining structural properties of glass and the thermal insulation capabilities of aerogel with the aesthetic and daylight-transmitting qualities of both. This paper describes the development and thermal and structural characterization and simulation of a highly thermally insulating aerogel glass brick. The aim was to create an aesthetically pleasing building component with excellent thermal insulation properties that is capable of transmitting daylight. This paper explores the design, development, and thermal simulations of an aerogel glass brick, as well as guarded hot-plate measurements and a compression experiment. Measurements of thermal insulating properties and simulations revealed that the aerogel glass brick could reduce energy consumption significantly compared to other conventional building materials for perimeter walls, while also transmitting daylight. Additionally, its aesthetic qualities can make it suitable not only for use in modern construction projects, but also in refurbishment of older objects. The measured thermal conductivity is 53 mW/(m∙K), in agreement with thermal simulation results of 51 mW/(m∙K), and the measured compressive strength of the brick is 45 MPa. These data suggest that the aerogel glass brick is a viable option for architects and engineers looking for a sustainable and efficient construction component for perimeter walls. Structurally, the brick should allow building large and high spans and its thermal insulation properties can significantly reduce energy consumption, while its aesthetic and daylight-transmitting qualities make it visually appealing. Keywords: Aerogel, energy savings, circadian rhythm, thermal insulation, daylight transmitting, Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1 CISBAT 2023 Journal of Physics: Conference Series IOP Publishing 2600 (2023) 112015 doi:10.1088/1742-6596/2600/11/112015 1. Introduction Building envelope is a crucial building element for regulating the relationship between the inside and outside environment. In particular, they play an important role in building energy efficiency and thermal comfort, regulating energy transfer and keeping the inside protected from the outside conditions. This is most relevant during the cold and excessively hot times of the year. Thus, the building envelope determines the requirements for heating and cooling. With the developments in building envelope technology in recent decades, building energy efficiency requirements have been increased strongly. Besides regulating heat transfer, the building envelope should address the use specific requirements for the transfer of daylight. If the envelope transmits light, ideally it should also offer the necessary amount of shading, and glare protection. However, most envelope systems are either opaque – providing total protection from the excessive sun but completely eliminating daylight – or transparent – providing daylight, visual connection, but offering no protection from glare or excessive light, and without providing adequate privacy in some applications. This conflict of interest is particularly important in light of the more pronounced recommendations to expose oneself regularly to natural light in order to address the lack of daylight exposure [1] which is a prerequisite for a healthy circadian rhythm. Targeting this gap between the existing opaque and transparent solutions, here we present a new building envelope technology, the translucent aerogel glass brick (Figure 1), which can potentially provide daylight for the interior without disturbing glare or loss of privacy (Figure 2) and at the same time, has a low thermal conductivity and thus also assures good insulation and thermal comfort. Figure 1 Translucent aerogel glass-brick prototype. Brick connectors and glass are transparent, aerogel filling offers translucent behavior for diffusive daylight. 2 CISBAT 2023 Journal of Physics: Conference Series IOP Publishing 2600 (2023) 112015 doi:10.1088/1742-6596/2600/11/112015 Figure 2 Visualization of the glazed wall made with translucent aerogel brick. By using bricks, it is possible to extend the aesthetic possibilities and enable continuous frame-free construction.[2] 2. Material and Methods We prepared numerous 2D designs for the brick, varying in the dimensions, materials and internal details. Four glass panels, with dimensions 500x84 mm, cut out of float glass with thickness 12 mm were connected with epoxy resin connectors. Various designs for spacer were simulated for heat flow and temperature distribution using open source Therm 7.6 (program developed by Berkeley Lab [3]). Using two-dimensional screening allowed to verify also numerous brick designs. The boundary conditions for simulations were set according to the Swiss standards for U-value calculation [4], for outside temperature of -8°C and for an interior 20°C, with resulting temperature difference of 28°C. For accurate evaluation of the whole brick with its sealing, a three-dimensional simulation in Physibel's Trisco software was used, to observe possible thermal bridging of the covering envelope of the individual bricks. The boundary conditions were set similarly accordant to Swiss standard as in previous 2D simulations. A brick with dimensions of 500 mm x 136 mm x 84 mm was tested for compressive strength (Figure 3) using a compression testing apparatus from Alfred J. Amsler & Co. Schaffhausen, Switzerland, with a maximum capacity of 5000 kN. The brick was sandwiched between a wood fiber boards for an even redistribution of forces. Thermal conductivity of the bricks was measured on a large-scale guarded hot-place device (Figure 4) following the criteria of standards SN EN 12667 and ISO 8302. For that, 6 rows of bricks were placed into the device, resulting in dimensions of 500 mm x 510 mm with 136 mm thickness (three full bricks and six half bricks) without glue or mortar and a gap between bricks in both direction of roughly 2 mm. Details on the methodology are described in previous detailed study [2]. 3 CISBAT 2023 Journal of Physics: Conference Series IOP Publishing 2600 (2023) 112015 doi:10.1088/1742-6596/2600/11/112015 Figure 3. Measurement of compression strength. The brick was placed between wood fibre board to minimize irregularities of the surface and to redistribute forces during the experiment. Figure 4 Thermal conductivity measurement setup in big guarded hot plate device. (a) Mock-up wall consisting of three whole and six half bricks to create proper overlapped cladding on the cold plate of the apparatus. (b) Brick wall sample covered with the hot plate (red color in scheme) and grey EPS reference sample (grey) with thickness 100 mm. In the final setting top cold plate is lowered (dark blue) as shown in the scheme on bottom left and sides filled with insulation (light grey). Figure 5 Temperature distribution for an aerogel-filled glass brick based on thermal simulations performed with Trisco. (b) top view, d) cross-section. [2] 4 CISBAT 2023 Journal of Physics: Conference Series IOP Publishing 2600 (2023) 112015 doi:10.1088/1742-6596/2600/11/112015 3. Results and Discussion Thermal and mechanical performance The thermal simulation resulted in a U-value of 0.350 W/(m2∙K) for thickness 136 mm, which corresponds to thermal conductivity 50.5 mW/(m∙K). This result of simulation is in accordance with the measured values of the hot plate measurement device of 0.365 W/(m2∙K) and 53.0 mW/(m∙K), for the U-value and thermal conductivity, respectively. The temperature distribution according to the thermal simulation (Figure 5) suggested no visible thermal bridges in the structure of the brick and an even redistribution of the temperature near the faces of the bricks. The measured compressive strength was 44.9 MPa, with a maximum applied force of 3042 kN during the overall collapse of the brick structure. More details on methods are elaborated in another article on the brick [2]. Table 1 Summary of simulations and measurements for thermal and structural assessment Material Equivalent thermal conductivity [mW/(m∙K)] U-value / Thermal transmittance [W/(m2∙K)] [ MPa ] Light transmission [%] ** Simulated 50.5* 0.350 -- - Measured 53.0 0.365* 44.9 - Compressive strength * calculated ** not measured due to lack of standard test for thick light diffusive component. Table source: [2] The aerogel brick has a remarkably low thermal conductivity of 53.0 mW/(m∙K), which is lower than any reported thermal conductivity of commercial insulating brick products or scientific prototypes currently in development. The best-performing, opaque insulating brick block prototype, for instance has a thermal conductivity of 59 mW/(m∙K) [5]. With a thickness of 136 mm, the aerogel glass brick has a U-value of 0.365 W/(m2∙K) according to the measurement, which is higher (i.e., less efficient) than the legal requirements for new opaque walls in central Europe (i.e. 0.17 W/(m2∙K) in Switzerland [6], [4]), but significantly lower (more efficient) than standard requirements for windows (1.0 W/(m2∙K)) in Switzerland [6]). If necessary, the brick can be designed thicker to achieve even better thermal insulation. Results suggest that the glass brick allows for great insulating property with a single layer for a ready-touse perimeter wall, eliminating the need for additional finish layers, reducing construction time and operational costs of the building. Figure 6 Characteristics of new aerogel glass bricks. (a)Compressive strength 44.9 MPa (b) Thickness of the wall to achieve U-value 0.22 W/(m2·K) (c) Visible light transmission is estimated around 35 percent based on properties of aerogel granulate. Source: [2] 5 CISBAT 2023 Journal of Physics: Conference Series IOP Publishing 2600 (2023) 112015 doi:10.1088/1742-6596/2600/11/112015 Figure7 Brick structure appears semi-transparent, allowing up to approx. 30 percent of light to penetrate [2] [7] , which can be utilized to brighten interiors by utilization of directsunlight or diffused skylight. 4. Conclusions The aerogel glass brick offers promising characteristics provided in Table 1 and Figure 6, which can be utilized in the building industry and architecture. Translucency allows sunlight and daylight inside (Figure 1, Figure 2 and Figure 7), diffusing the direct light, and bringing it deeper into the space. This may help to save energy and maintain a healthy biorhythm by circadian synchronisation for humans, animals and plants. The glass brick provides effective thermal insulation with a low thickness of the perimeter wall, while enabling passive solar gains through infrared radiation. Also, it has strong loadbearing properties self-carrying, with no necessity for loadbearing and dividing frames or reinforcements. Furthermore, there is no need for a variety of specialized labor work by its quasi-monolithic feature. The brick offers architects, civil engineers, home-planning clients and other decision-makers a new tool for architectural design of the space. Acknowledgements This research was supported by Velux Stiftung, project No. 1440 on development of thermal superinsulating translucent glass brick for diffusive daylight. The idea was developed with support of the European Union’s Horizon 2020 Research and Innovation program under the Marie Skłodowska-Curie Actions, grant agreement No. 746992. References [1] M. N. Mead, “Benefits of Sunlight: A Bright Spot for Human Health,” Environ. Health Perspect., vol. 116, no. 4, pp. A160-7, 2008. [2] M. Ganobjak et al., “Get the light & keep the warmth - A highly insulating, translucent aerogel glass brick for building envelopes,” J. Build. Eng., vol. 64, no. November 2022, p. 105600, 2023. [3] Berkeley lab, “Therm - Two-Dimensional Building Heat-Transfer Modeling,” 2019. [Online]. Available: https://windows.lbl.gov/software/therm. [Accessed: 31-May-2021]. [4] “SIA 380/1:2016 Heizwärmebedarf : Standard.” p. 60, 2016. [5] J. Wernery, A. Ben-Ishai, B. Binder, and S. Brunner, “Aerobrick - An aerogel-filled insulating brick,” in Energy Procedia, 2017, vol. 134, pp. 490–498. [6] Konferenz Kantonaler Energiedirektoren, “EN-100 bis EN-142 (MuKEn 2014).” [Online]. Available: https://www.endk.ch/de/fachleute-1/energienachweis/EN-101 bis EN-141. [Accessed: 03-Jun-2022]. [7] Cabot, “AEROGEL LUMIRA ® TRANSLUCENT AEROGEL LA1000 ; LA2000 : datasheet.” 6