Coole Fenster - Windows with shading optimising the trade-off between summery overheating, wintery heat protection and adequate illumination

Windows with their associated components such as sun and glare protection are optimised as a holistic building equipment unit regarding different seasonal requirements in light of the climate crisis. The results serve as a basis for new developments in the window and shading technology in order to provide summery and wintery heat protection as well as adequate natural illumination over the year.

Short Description



Starting point / Motivation

The climate crisis is omnipresent and, based on current knowledge, can no longer be stopped. Even now, especially in densely built-up urban areas, there is a noticeable increase in hot days with temperatures way above 30 °C, followed by „tropical nights" during which the temperature does not drop below 20 °C. Physiologically unsuitable climatic conditions such as these have a negative effect on health and comfort of residential dwellers. At the same time, a pronounced heating period can still be expected in winter even under the most unfavourable projections of global warming.

While thermal protection during the cold period has been the focus for a long time, protection against overheating during summer has only come to attention during the past decade. In many cases this is counteracted by using small air conditioning units with poor energy efficiency, not considering the high energy consumption during operation. In addition to the high use of resources, there are the problems of waste heat and noise.

On the other hand, there is great potential of external sunblinds to reduce interior overheating during summer. In previous research concerning sunblinds and windows, the focus has so far mostly been placed either on protection against overheating in summer or on thermal protection during winter. However, this one-sided view is problematic, since the two cases place opposing demands on the window. In addition, daylighting is usually not considered.

Contents and goals

In this project, the window and its additional components (sunblinds, etc.) are, for the first time, understood as a holistic building equipment unit that optimally meets the respective requirements of the annual seasons and the daily requirements. To this end, the aspects of sun protection, daylight supply, glare protection, control algorithms, ventilation and energy saving (heating and, if necessary, cooling) are to be optimized during the year.

The broad foundation of the present exploratory research also allows the potential of technologies to be considered that have not played a role in residential construction up to now, e.g. electrochromic glazing. In summary, the higher-ranking project goal that can be derived from this motivation, which is also to be understood in terms of the EPBD ("dynamic façade"), is:

Holistic optimization of the components of the passive building equipment unit "cool windows" and their interaction in order to be able to ensure a physiologically suitable indoor climate in urban residential buildings under future climate conditions, if possible, without the use of active cooling.


The method of this optimisation consists of a comprehensive parametric study with associated sensitivity analysis. Manual or automated statistics-based optimisation algorithms, which are implemented with the help of state-of-the-art building simulation tools, are used on a model building.

Expected Results

With the completion of the exploratory research project, holistically suitable implementation concepts for the building equipment unit "cool windows", pre-evaluated for technical and economic feasibility, should be available.

These include concepts for a seasonally optimized solar and daylighting management with the associated control algorithms, which together result in the lowest possible energy consumption and thus low CO2 emissions and will provide a basis for further RDI projects. For easier usability, the generated result data is bundled and processed in the form of a database as part of the exploratory research project.

Project Images

Terms of use: The pictures listed underneath the header “Project Pictures” originate from the projects in the frame of the programmes City of Tomorrow, Building of Tomorrow and the IEA Research Cooperation. They may be used credited for non-commercial purposes under the Creative Commons License Attribution-NonCommercial (CC BY-NC).

Project Partners

Project management

Dipl.-HTL-Ing. Klaus Peter Schober - Holzforschung Austria

Project or cooperation partners

DI Heinz Ferk - TU Graz

Contact Address

Holzforschung Austria
Franz Grill-Gasse 6
A-1030 Vienna
Tel.: +43 (1) 798 26230