Supplementation of a standard for toughened safety glass with stress-optical measurement methods and analytical concepts to reduce destructive tests

In the building industry, construction product requirements are placed on toughened safety glass (ESG) to meet the prescribed safety level. The most important properties in this regard are mechanical bending strength and fracture structure. Tests to ensure these properties have not changed since the relevant European mirrored product standard EN 12150 was first published in 1996. It is mandatory to perform destructive tests on concomitantly (daily) produced small glass elements (0.36m x 1.1m) to determine fracture structure and flexural strength. Innovative stress-optical methods and analysis concepts are only considered to a limited extent in current standards.

The aim of the project is therefore to draft an amendment to the European standard to include stress-optical measurement methods and analytical concepts to reduce destructive tests for determining the bending strength and fracture structure in thermally toughened single-pane safety glass.

Windows and facade systems with vacuum insulating glass

Glass, windows and facades are among the most important construction elements in architecture for saving energy and using solar energy. The central component of windows and facades is glass, which accounts for 80 to 90% of the total. What is needed are “slim” frames that nevertheless ensure a Uw value as much as possible of 0.6 W/(m²K) and highly thermally insulating and multifunctional “slim” glass with a Ug value of 0.3 W/(m²K). The Building Energy Act (GEG- Gebäude-Energie-Gesetz), which has been in force since November 2020, means that requirements for window and facade systems in new buildings can only be met with 4-pane insulating glass or by using vacuum glass as components of multifunctional insulating glass units (VIG+ Verglasung bestehend aus Vakuum-Isolierglas und Vorsatzscheibe). Given the current standard of triple insulating glass, transparent areas of buildings would have to be reduced in order to comply with the specifications of the GEG. This standard does not meet the expectations of architects, planners and end users. When renovating existing buildings, slim frame and glass systems with the above Ug and Uw values are also advantageous. Existing double-glazed units can be replaced very efficiently with new VIG+ units of the same thickness, with significantly better energy efficiency.

The overall objective of this research project is to develop highly thermally insulating and slim window and facade systems with hybrid glazing consisting of vacuum insulating glass and face glazing (VIG+) in order to produce mutually optimized systems, to test these and to apply them in practise. In view of the new Building Energy Act (GEG), FFS-VIG stipulates the prerequisite that window areas in new buildings can remain the same size or even be larger. In addition, the low installation thickness of VIG+ enables its use in existing buildings, thus opening up enormous energy-saving potential. A front glass pane guarantees a high level of durability of vacuum insulating glass systems, which is to be tested and proven in the project, and enables the insertion of multifunctional components (BIPV, switchable glazing, etc.). Due to the considerable improvement in insulation value, the amount of heat loss through the window area is halved compared to current triple insulating glazing. However, there is still a lack of efficient system solutions in the field of thermally and physically optimized frames and facades in order to be able to exploit this potential. For this reason, the development of practicable and economical system solutions for frames/VIG+ within the framework of FFS-VIG is essential for a rapid market entry and broad market penetration. Furthermore, the establishment of product standards (VIG and VIG+) for the European market as well as the achievement of general building inspectorate approvals (abZ- allgemeinen bauaufsichtlichen Zulassungen ) for this new type of glass will accelerate the application of such systems in practice.

Draft standards for thermal breakage to determine the thermal stress of glass and glass PV modules (BIPV- Belastung von Glas und Glas-PV-Modulen) in the construction industry

Due to the large number of cases of damage, research projects have been carried out in the past to determine the thermal stress of facade glazing, but these have not been incorporated into (German) standards. As a result of recent efforts and measures in terms of energy transition, building-integrated photovoltaic modules (BIPV modules) are gaining more and more importance as a component of an energy efficient solar building envelope, which explains the growing need for research in this field.

The project aims at a comprehensive, detailed examination of façade glazing and glass PV modules (BIPV) in buildings, which are thermally stressed by solar radiation and (can) typically break in critical constellations, and then to develop a draft standard based on the results of these investigations. On the one hand, a basic understanding of the relevant climatic and design parameters and their interrelationships will be developed. In addition, the focus here is on the evaluation and provision of reliable (freely) available climatic data in Europe and Germany. On the other hand, approaches within parameters of the French standard (NF DTU 39 P3), which involves the design of thermally stressed glass and is quasi “state-of-the-art” and which is to date the only set of rules being “unofficially” applied throughout Europe in current construction practice, will be considered more closely as an orientation. The purpose of the project is to reduce or avoid the occurrence of thermally induced glass breakage (thermal breakage) through European standardization. In this way, financial economic damage can be prevented.

The strength of thermally relaxed float glass made of soda lime silicate glass at high temperatures to transformation range.

The objective of the research project is to experimentally investigate the temperature dependence of the flexural strength of thermally relaxed float glass within a temperature range from room temperature through to glass transition temperature range. In order to make predictions about the failure of glass during its thermal toughening and additive manufacturing, certain parameters must be known, including the flexural tensile strength of the glass within the relevant temperature range, the associated stress rate from the cooling process and the typical damage states of the glass surface resulting from upstream production processes. For soda-lime-silicate glass as well as borosilicate glass, only very few experimental research results are available with respect to the temperature dependence of the bending tensile strength within the range up to glass transition temperature. Previous work has focused on the temperature dependence of fracture toughness (soda-lime-silicate glass) and the temperature dependence of bending tensile strength (borosilicate glass). In addition, previous tests were mainly carried out at high stress rates of up to 320 MPa/s. The duration of the cooling process during thermal toughening and the cooling process during additive manufacturing suggests that the stress rate should be lower for the applicability of results in civil engineering. For this reason, in this research project, the flexural tensile strength at high temperatures in the range up to the glass transition temperature and with two stress rates (2 MPa/s, 20 MPa/s) will be investigated in particular. The investigation of the influence of temperature and stress rate will be carried out on specimens with surface damage typical of the process (defined scratches, cylindrical holes drilled using the diamond drilling method). Since soda-lime-silicate glass is primarily used in the construction industry, the investigations will be carried out mainly using float glass made of soda-lime-silicate glass, including a series of tests using borosilicate glass for the sake of comparison.

Optimization of material- and lay-out-technical parameters of aeration elements in biological wastewater treatment

Aeration plants are the most frequently used type of plants worldwide for biological wastewater treatment in the industrial and municipal sector. The aeration system used in this process requires up to 80 % of the total energy demand of a wastewater treatment plant during biological wastewater treatment, so that the aeration system and the aeration elements installed in it must be given priority in energy optimization (Wagner and Stenstrom, 2014). The energy efficiency of an aeration system is largely determined by two parameters: 1) Oxygen utilization represents the fraction of oxygen dissolved in the activated sludge from the injected ambient air. The mass transfer depends partly on air bubble size and bubble rise time, as well as on wastewater-specific parameters such as the activated sludge matrix. To ensure an energy efficient operation, the maximum possible oxygen utilization should be achieved. This can be achieved by blowing in the smallest possible air bubbles. 2) The pressure drop in the aeration element describes the additional backpressure that a compressor must apply in order to introduce ambient air through the perforated aeration membrane into the water column above. The pressure drop is largely determined by material properties of the aerator membrane and its changes during operation with activated sludge. For an energy efficient operation, the pressure loss should be kept as low as possible. This can be achieved, by periodically cleaning the aeration elements, for example. Fine-bubble compressed air aeration systems using aeration elements in the form of plates, pipes and sheets made of the materials EPDM, silicone and TPU are predominantly used today (DWA 2017). These elements result in a significantly higher level of oxygen utilization, but at the same time result in a higher loss of pressure compared to coarse-bubble pressurized aeration systems.

The overall research objective of the WOBeS project is to increase the energy efficiency of pressurized aeration systems through adapted process and operational management. As part of the optimization of material and lay-out parameters of aeration elements in biological wastewater treatment, the energy disadvantage of the higher pressure loss in fine-bubble pressure aerators compared to coarse-bubble pressure aerators is to be reduced through further investigation of the properties of the membrane material. At the same time, the off-gas behavior of the membrane materials investigated must be considered in order to generate the smallest possible air bubbles by means of suitable perforation, thereby increasing oxygen utilization.