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In 2016, the Insitut für Fenstertechnik e.V. (ift Rosenheim) is celebrating its 50th anniversary. According to the motto ‘ift Rosenheim – 50 years of service to the industry’, the technical development is presented in a ten-part series of articles. The individual articles are reflecting timeframes of 5 years from founding of the institute. They enable a short glance at the events at that time, take up as a key aspect a pioneering research project at that time, summarize goals, contents as well as results, then illustrate the further development as well as the impact thereof on the industry, and the current state of the art.
Design features for windows
The 80s
New technologies and materials, the request for greater living comfort as well as the methods of serial production determined the window development. The practical value of the new “window generation” was not easy to evaluate and the adaption of the technical guidelines was unavoidable. First, they tried to regulate all technical details normatively, but that limited the development. Therefore, the specifications were loosened and only the limits for the technical correct performance defined.
Aim of the Research Project
Only fundamental should be determined with further window standardization. Therefore, building owner, architects and construction manager had to dispose of the necessary knowledge. The Ministry for Regional Planning, Building and Urban Development commissioned ift Rosenheim to assemble the necessary characteristics of construction and evaluation of windows.
The development to a “complexer window" regarding frame, hardware and appearance as well as "excessive" requirements on technical parameters, surface as well as aesthetic details were also focus of critism due to the resulting cost increases. However, objective decision-making aids were missing. A foundation for an acceptable solution should be found with the research project „Design Features for Windows”.
Results of the Research Project
The research report “Design Features for Windows” [3] was published in 1986 and offered support for daily work regarding to functional performance specifications, the definition of requirements and the construction details. Fundamental assessment criteria to materials, accessories, window types and window systems created a good basis for planning and the systematic consideration of all influences allows an objective evaluation. Examples and a compilation of the guidelines and tables (glazing, coating, lamination, compatibility and static) compiled by ift Rosenheim complete the report.
uPVC windows are gaining market shares
The first uPVC windows in 1956 were made of a steel frame coated with soft PVC. In 1959, windows made of hard PVC followed (nowadays PVC-U). Profile geometries and constructions were not developed appropriate for the material involved and were oriented towards wooden windows. The variety of the systems developed in the subsequent period differs in number and positioning of sealants and cavity in the profiles. In the 60s and 70s, also profiles made of glass fiber reinforced plastic, polyurethane and wood-plastic were offered.
In the 60s, the only objective evaluation size was the a-value (tightness). This value was highlighted as an exclusive quality characteristic, especially for uPVC windows. The newly developed test possibilities of other properties brought further developments, which were supported by RAL-quality control [4] as well as by the results of ift-research work regarding rebate design [5] and glazing [6] (image 1).
a) Influence of number of chambers (and profile thickness) on Uf value
b) Further measures for the improvement of the Uf value
The growing part in the refurbishment made also technical regulations for the installation and the sealing necessary. On basis of ift-research reports [7, 8], the “Installation Guidelines for uPVC Windows” [9] and the guideline „Testing of Mechanical Connection at uPVC Windows“ were issued. The guidelines have been updated since and are still valid [12].
The developments led to an adjustment of the constructions in the 80s and 90s and were characterized by extruded, hard PVC profiles with a main chamber including metallic reinforcement profile as well as at least one antechamber in mainly white colour.
The growing part in the refurbishment made also technical regulations for the installation and the sealing necessary. On basis of ift-research reports [7, 8], the “Installation Guidelines for uPVC Windows” [9] and the guideline „Testing of Mechanical Connection at uPVC Windows“ were issued. The guidelines have been updated since and are still valid [12].
The developments led to an adjustment of the constructions in the 80s and 90s and were characterized by extruded, hard PVC profiles with a main chamber including metallic reinforcement profile as well as at least one antechamber in mainly white colour.
Since the middle of 2000, the constructive development is also driven by the glass bonding, as the effective properties of the glass allows large window casements with narrow profile projected width and the reduction of massive steel reinforcements.
uPVC windows nowadays
The challenge of the present are large-sized casement and the high casement weights, additional functions like ventilation, sun protection, safety aspects to be integrated, the variety of design possibilities regarding surface, forms, colours as well as the open communication of the consequences regarding the environment and health.
By focusing on the thermal insulation, strongly asymmetric profile geometries were developed and stiffening elements (reinforcement) moved in the internal area. In addition, the share of coloured profiles increased. However, other thermal deformations (shrinkage and linear expansion) require higher operating forces and leakages at different climates (image 3), that can cause functional limitations like jamming elements, lower air and water tightness as well as lower sound reduction values.
Normative limits for the maximum deformation of uPVC windows due to thermal load are nonexistent, but the function has to be guaranteed. The system houses make clear specifications regarding production and mounting in the system descriptions and processing instructions, e.g. the reduction of maximum sizes depending on colour, use of suitable reinforcement profiles (geometry, wall thickness, steel quality, etc.), additional ventilation holes and fixings to the wall.
b) Example of a ventilation system in the window profile (source: Rehau AG + Co)
The sash weight increases substantially due to triple insulating glass. Standard hardware meets the maximum capacity with normal superstructures and large sash formats. This applies particularly at special glasses (e.g. acoustic insulation, burglar resistance). The fixation of the hardware and the construction of the screw connections with compliance of the determined processing parameters are substantial for the safety in use of windows.
The cavities and the modular design enable the integration of additional functions and additional components. The variable configuration with fans, glasses, hardware with additional functions is easily possible. Combinations with aluminum shells, integral windows and composite constructions provide a large design and performance range (image 4).
The free combination of modules to design the favourite window is still utopia. The consistent separation of functions, e.g. support structure like thermal insulation and design. However, the currently most important additional function burglar resistance is already solved constructively for a long time. Optimization potential still applies with mounting and at constructive weaknesses like coupling.
The increasing resource scarcity as well as environmental compatibility remain the core topics. In the past, chlorine content and heavy metal stabilizers like lead were problematic for uPVC windows and alternative stabilizers as well as recycling concepts for old windows and production waste had to be developed. However, current research projects regarding loads by VOC emissions and erosions have delivered no remarkable results [13, 14].
Summary
uPVC windows have been developed dynamically in the last decades. The driving force was, as so often – the optimisation of the thermal insulation. Further foci in development are on the improvement of comfort, automation, safety, sustainability and energy efficiency; also the increasing demands regarding environmental impacts and sustainability are fulfilled. An action linked ecologically and economically is indispensable.
Literature
- 25 Years Institut für Fenstertechnik e.V.; An overview.
Institut für Fenstertechnik e.V., Rosenheim 1991 - Froelich, H.:
Decision criteria for the selection of windows.
Research report of Institut für Fenstertechnik e.V., Rosenheim 1981 - Froelich, H.; Hepp, B.; Löffel, G.; Schmid, J.:
Design features for windows.
Research report of Institut für Fenstertechnik e.V., Rosenheim 1986 - Quality Regulations and Test Specifications for Plactic Windows RAL-RG 716/1.
RAL Committee on Delivery Conditions and Quality Control, Frankfurt/Main, May 1977 - Schmid, J.; Stiell, W.:
Rebate design at window.
Research report of Institut für Fenstertechnik e.V., Rosenheim 1976 - Feldmeier, F.; Heinrich, R.; Schmid, J.; Stiell, W.:
Ageing behaviour of insulating glass unit.
Research report of Institut für Fenstertechnik e.V., Rosenheim 1984 - Seifert, E.; Daler, R.; Heine, F.:
Windows at renovation of an old building.
Research report of Institut für Fenstertechnik e.V., Rosenheim 1979 - Blaschke, K.; Schmid, J.; Stiell, W.:
Connection of window to wall.
Research report of Institut für Fenstertechnik e.V., Rosenheim 1977 - Installation guidelines for uPVC windows.
Editor: ift Rosenheim and RAL, Bonn (as part of Quality Regulations and Test Specifications for Plactic Windows RAL-RG 716/1) 1985 - Leuschner, I.:
Trends of uPVC windows.
ift Rosenheim, 2002 - Lass, J. P.:
Work of art uPVC window.
Conference transcript Rosenheim Window and Façade Conference, ift Rosenheim 2011 - Guideline for Mounting.
Editor: RAL Quality Assurance Association: Windows and Doors, Frankfurt 2014 - Bliemetsrieder, B.:
VOC emissions of plastic windows.
Research report of Institut für Fenstertechnik e.V., Rosenheim 2015 - Bliemetsrieder, B.; Kaube, M.; Scherer, C.; Schwerd, R.; Schwitalla, C.; Externbrink, F.:
Erosions of building elements.
ift Rosenheim and Fraunhofer-Institut für Bauphysik IBP, location Holzkirchen, 2016
Gabriele Tengler
Dipl.-Ing. (FH) Gabriele Tengler as assistant head of PR & Communication and employee at ift Rosenheim since 1978. In addition, responsible for many years for the Technical Hotline and for more than 20 years for the organisation of the Rosenheim Window and Façade Conference. For more than 35 years now, she takes care of the public relations at ift to process the compiled knowledge target-specificly and to provide it to the industry.
Ingo Leuschner
Dipl.-Ing. (FH) Ingo Leuschner († 2023) was a member of staff at ift Rosenheim since 1997. His activities included the technical Assistant to Director of Institute and the management of various research projects (wood facades, hardware, associated constructions, surface technology). He held training courses, seminars as well as lectures and was head of the ift Centre of Technical Experts since 2014. Since 2017, he was Head of the Technique Division, a member of the Executive Board with power of attorney and, since August 2021, Deputy Technical Director of Institute.
