Pure glass façade designs are becoming more and more popular. Technical complexity, environmental changes, and requirements for energy efficiency and overall sustainability are some of the key challenges in modern architectural designs.
Structural silicones are enabling technologies which help realize structural designs, however, one might be surprised by the untouched potential silicones can offer in response to the ever-changing world of architecture, engineering, and construction for smart aesthetics, energy efficiency, durability, or profitability of high-performance façades.
The Smart Power of Crystal Clear…enhancing aesthetics, performance and efficiency
Architectural trends in modern commercial façades are moving towards larger glass surfaces and slimmer frame designs utilizing structural glazing, which produces sleek and flush façade skins, free flowing structures and finally increased transparency of the design. Although necessary, the structural and weather seal joints which are the anchoring and connecting elements between the transparent glass lites, represent the remaining visible ‘bottleneck’ in the continued architectural quest to maximize facade transparency and blur the visual barrier between the interior and exterior environments, as (typically) the adhesives being used are not necessarily both transparent and durable. Transparent structurally performing silicones such as crystal clear film adhesives DOWSIL ™TSSA/TSSL or crystal clear sealants such as DOWSIL™ 2400 Silicone hotmelt [1, 2] have enabled increased transparency of the façade and continue to push the boundaries of creativity, strength and aesthetics.
Fully transparent designed insulating glass units are unfortunately not always possible when glare management and energy efficiency are also priorities. An elegant way to maintain a flush glazed façade and avoid exterior/interior blinds is to work with a combination of glass and different ‘filter’ elements such as metallized plastic meshes, capillary systems or timber veneer elements. These elements all provide an aesthetically pleasing daylighting control [3] capability but are typically integrated into the cavity of an insulating glass unit since their make-up prevents them from being laminated between two glasses at high temperature using conventional interlayers such as PVB.
Heat flow is concentrating on the path of least resistance, which the secondary sealant has typically become in optimized IGU designs, bonded on a frame or purely glass to glass
A new, fully transparent, silicone technology was recently developed to allow for large scale decorative lamination at room temperature. Successful trials have confirmed the potential of the process to laminate a metallized mesh insert without aesthetic impact to the filtering medium and provide it with long term protection typically obtained through the use of durable silicone. Technically a decorative silicone laminate provides a “perfect edge” as it is compatible with the other façade silicone technologies it is in direct contact with. To produce laminates with conventional interlayers, a significant amount of energy is needed by autoclaving. A room temperature curing laminate can help lower cost whilst enhancing overall sustainability. A smart way of realizing aesthetics and performance whilst enhancing process, cost and efficiency.
The Smart Power of “Warm” Silicones…enhancing energy efficiency, performance and cost
Designs should not only focus on aesthetics but also take into consideration functional requirements. Energy regulations and climate policy targets have established strict requirements for future buildings. According to the Energy Performance of Buildings Directive, by 2020 all new buildings in the EU will have to be built as “Nearly Zero-Energy Buildings” (NZEB) [4]. These targets impose high expectations on building envelope performance and pose challenges in building design. This NZEB initiative is stretching the limits of façade systems or elements, which brings a significant contribution to the heat flow in the building.
Amongst them, vision panels often present a preferential path across the façade as far as heat transfer is concerned. To improve performance, the insulating glass industry developed improved systems, like triple insulating glass units (IGUs) and inert gas filled IGUs. In such a system the center of the glass pane typically exhibits excellent thermal insulation properties. Since heat flow favors the path of least resistance, it will be more significant at discontinuities in the envelope including edges of glazing. The better the insulation at the center glazing, the higher the relative contribution of the losses at the edge. In some cases it even becomes the limiting factor to meet industry specifications, thermally efficient spacer bars have been commercialized in order to reduce the contribution of the edge to the heat flow. These devices are referred to as “warm edge” spacers in the insulating glass market and are commonly used in thermally efficient façades. Further energy optimization of curtain walls comes at a high price and often in conjunction with a design change, since the achieved performance improvements are not sufficient, which adds complexity and costs to the system design. The challenge is therefore to develop solutions providing a better performance at a reasonable cost and low complexity to ensure ease of adoption by the market and, consequently, a significant impact on the improvement of the building stock.
Coming back to IGU optimization, with the above mentioned incremental performance improvements through gas filling and warm edge spacer, the “weak point” is now the secondary sealant as part of the IG edge.
Using DOWSIL ™ 3364 WARM EDGE IG Sealant as a secondary silicone sealant, the heat flux is reduced
Ucw,eff gain (%) for different IGU dimensions using DOWSIL™ 3364 Warm Edge IG Sealant instead of standard silicone on a conventional toggle system (Schueco, FW60+ SG frame)
Where the secondary sealant may seem to make a limited contribution in comparison to the surface of the glass and gas filling, the total linear meters of sealant do add up on a façade and could become a significant element of its performance. Linear heat loss at the glass edge can be as big as the heat loss through the framing system itself. Reducing the linear heat loss through the edge is therefore a potentially important contribution to the reduction of the overall heat loss through the vision area and additionally mitigating risk of condensation around the perimeter of the glazing.
The use of the newly developed “warm edge” structural silicone for insulating glass, such as DOWSIL™ 3364 Warm Edge IG Sealant, with a thermal conductivity of 0,19W/mK -about 45% lower compared to a standard silicone with 0,35W/mK [5]-, leads to significant improvements in the reduction of the heat loss through the edge and results in a reduced heat flow through the façade: a complete “WARM EDGE”.
Depending on the type of system, unitized, toggle, frame type, dimensions, etc the overall façade UCW-value improvement can be as high as 5 % in thermal efficiency [6] – which is significant at the façade component level. To achieve that, only the conventional sealant needs to be replaced with the DOWSIL™ 3364 – no design change is needed, no change of frame, glazing or other components.
It is interesting to also note that the improvement by using DOWSIL™ 3364 is proportional to the energy performance of the facade. The better the facade is, the more it will benefit from the use of the DOWSIL™ 3364 as a secondary sealant. Designing façades with the “warm edge” silicone can help to enhance living comfort by reducing condensation and mold growth in proximity of the pane edges with the observed increased surface temperature (up to +1°C). Hence, the importance of this material will continue to increase with energy demands put on facades.
The Smart Power of Fast Cure Performance & 3D Printing…enhancing productivity and efficiency
The construction industry has traditionally been conservative, slow to innovate and relatively unsuccessful at boosting productivity [7]. In recent years, innovations during the actual construction phase are being observed as construction sites are modernized dramatically by digital fabrication technologies, such as robots for automated production which will help avoid delays, overspending and skilled labor shortages.
In comparison with the speed of production possible today thanks to these automated technologies, silicones
used for structural bonding are typically slow in use, needing several days up to weeks to achieve full hardening and adhesion properties, either in factory or on site. In order to answer the need for increased speed, DOWSIL™ 994 Ultra-Fast Bonding Sealant offers an adhesion build up to glass of 30 minutes which permits a significantly reduced cycle time in production while maintaining the required strength and durability of conventional silicones. DOWSIL™ 994 addresses the requirements of the ETAG002 [8] for structural applications in commercial façades, and by extension can be utilized in bonding applications across the commercial and residential construction space for windows, metal panel systems, natural and manufactured panels, solar/thermal applications, internal partitions, and more.
Additive manufacturing – also referred to as 3D printing – goes one step further in enabling productivity in the construction industry, in this instance through digital fabrication. One of the earliest uses for 3D printing in construction was to print tabletop scale models for architecture firms. However the many advantages of 3D printing in construction [9, 10] make it a near perfect match for the construction industry and several organizations have started experimenting using 3D printing to produce modular components of fullscale projects. Printed building elements only use the necessary amount of material, reducing costs and waste and lowering overall CO2 emissions of the project. From a productivity point of view, additive manufacturing can reduce labor through automation. It also offers increased production resolution which could be leveraged to reduce tolerances and hence improve construction time on site. Recent developments in 3D printing technologies offer the potential for near limitless freedom of design and the possibility to fabricate complex shapes on or off-site achieving the high degree of customization increasingly which is increasingly ubiquitous in today’s construction projects.
Making the concept of additive manufacturing in the construction industry more interesting is the increasing variety of 3D printable materials that continue to become available through innovation. The variety of possible materials which can be printed today span the spectrum of the familiar: cements, concrete, mortars, ceramics, metals, polymers, etc., to the not so familiar: biomaterial, cellulose, aerogels, and glass. Concrete printers have been used for residential houses [11] and bridges [12, 13]. Efforts are undertaken to use different local material including dirt, mud and sand [14] as the basis for construction, making it even easier and cheaper to construct in the first place. However, all the existing materials are rigid and few options are available to print flexible AND durable materials which are typically desired or needed to connect construction elements together. Under the EVOLV3D™ [15] umbrella Dow has created a range of 3D printable Si based elastomers. These materials possess the silicone performance well-known to the construction industry and introduce the power and versatility of silicone technology into the realm of 3D printing. Dow is actively innovating to make additive manufacturing for the construction industry a reality [16]. Additive manufacturing of strong, flexible and durable construction components supports the efficient and sustainable approach to the design and construction of highly customized built environments that are typically costly and time-consuming to achieve through traditional means of heating, beating, and treating building materials to suit the desired purpose of the moment.
Unleashing the Power of Silicones for Commercial Facades
Well known in the construction industry for more than 50 years, the unique properties of silicone continue to surprise and to bring innovative silicone-based solutions. Transparent and durable silicones address the demanding aesthetic needs and support the continuous pursuit of full transparency. Highly insulating silicones help provide a thermally homogeneous façade and answer the legal requirements of energy performance for buildings, with a minor impact on design and cost. Fast curing silicones and 3D printable silicones are the missing link which will enable a fully automated, fast and reliable construction process.
References
1. Silicones enabling crystal clear connections, V Hayez, IGS, 2016
2. Silicones enabling crystal clear bonding, V. Hayez, D.Culot, S. Yee, M. Plettau, Engineered Transparency (2016)
3. Okalux website https://www.okalux.com/
4. Official Journal L 153, 18 August 2010 p. 0013 – 0035 Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings.
5. EN ISO 10456:2010-05, Building materials and products – hygrothermal properties – tabulated values and procedure for determining declared and designed thermal values, European Committee for Standardization, Brussels, Belgium, 2010.
6. A newly developed silicone technology to improve thermal performance of curtain walls , V. Hayez, F. Gubbels, N. Buljan, Engineered Transparency, 2018
7. Will 3D printing remodel the construction industry? 23/1/2018, r. de Laubier, M. Wunder, S. Witthöft, C. Rothballer,www.bcg.com
8. ETAG002, Guideline for European Technical Assessment for Structural Sealant Glazing Systems, EOTA, 2012
9. A history of 3D printing in construction and what you need to know, Heather Head, 19 May 2017, Connect&Construct, www.connect.bim360. autodesk.com
10. 3D printing of buildings: construction of the sustainable houses of the future by BIM, EnergiaProcedia 134 (2017), 702711
11. You can now 3D-print a house in under a day
12. https://iaac.net/research-projects/large-scale-3dprinting/3d-printed-bridge/ accessed 8/11/2018
13. https://mx3d.com/projects/bridge-2/ accessed 8/11/2018
14. www.3Ders.org, ETH Zurich uses sand 3D printing to build 80m2 concrete Smart Slab for DFAB House, Jul 31, 2018 15. https://www.dow.com/en-us/news/press-releases/ dow-3d-printing-evolv3d accessed 8/11/2018 16. Patent applications: WO2016044547, WO2017040874, WO2017044735, WO2018183806, WO2018183803
This article first appeared in IGS Magazine’s Winter 2018 Issue – Read the full Magazine here for more thought-leadership from those spearheading the industry
Author: Valerie Hayez, Global Façade Engineering & Architectural Design Engineer at Dow Silicones
Valérie Hayez is Global Façade Engineering & Architectural Design Engineer for High Performance Building Solutions at Dow Silicones, based in Belgium. In her current role, she provides technical service to the design community, including façade system manufacturers, architects and engineers. She is responsible for identifying and communicating industry needs to Dow‘s Research and Development Community and supporting the development and commercialization of new products