Planners, building facility managers and users are increasingly setting a focus on the cooling of buildings. Especially in office and administrative buildings, air-conditioning units have become indispensable even in our latitudes. Room temperatures of over 30 °C in summer are no longer uncommon. In many cases, the entire period outside the heating season must now be considered a cooling period. The increase in outdoor temperatures due to climate change, an increase in heating loads due to solar gain from large windows or glass surfaces and an increase in internal heating loads due to technical equipment in general contribute to a rapid raise in cooling energy demand.

CoolAIR pursued the approach of a resource-saving reduction of cooling energy demand through energy-efficient natural night ventilation in combination with daylight-optimized shading. The aim was to develop an automated and predictive model-based control strategy for such a low-tech approach. By breaking down the control to room level, a highly flexible system is created that can fully utilize the passive cooling potential through night ventilation by using and partially automating already existing ventilation openings, without interconnection through a central building management system, and by means of Plug&Play.

The project results provide a valuable basis for further development work as well as for commercial implementation. The following innovations were developed in the project:

1. An intelligent control unit based on model predictive control was developed. The basis for the control strategy was a neural network (artificial intelligence method), which was trained and evaluated with the help of simulation results as well as measurement data from the test rooms. A reasonable minimum sensor configuration of only three sensors was defined in it. Furthermore, the option for partially opened outer casements was included in the mechanics and control system, which enables heat to be dissipated from the space between the box-type windows and thus significantly increases the efficiency of the sunshade hangings located in them.
2. Through computational flow simulations (CFD) and tracer gas measurements, it was possible to determine in detail the factors influencing room air exchange during window ventilation and to identify a methodology for estimating the potential of ventilative cooling from the results analysis.
3. In addition to the original planning, the project was able to develop a method for calculating the daylighting of a room without the need for a dedicated simulation. The model derived was introduced into standardization and will thus be available to a broad public in the future.

Methodologically, the project followed a transdisciplinary approach of empirical and simulation-based analysis of the developed concepts. The basis for this was both data from literature and long-term monitoring carried out over the entire duration of the project. The following main results can be mentioned:

• The night-time cooling potential in Austria can be used efficiently, especially in the interim periods, even if the number of nights that can be used due to climate change is reduced or shifted seasonally.
• For the model predictive control, framework conditions have been researched and the suitability for a maximum nightly discharge of heat storage mass with minimisation of the window opening cycles to one has been proven.
• It was shown how glare protection can be combined with good daylight utilisation in old buildings with high rooms and windows.
• It was demonstrated at the University of Continuing Education Krems and the Hofburg Vienna that box-type windows of different designs (Viennese and Graz type) can be automated for ventilative cooling. A minimal-invasive application was implemented at the Hofburg Vienna, which is not only functional but also complies with the requirements for the protection of historical buildings.
• From an economic point of view, this system scores with lower investment and operating costs compared to mechanical cooling concepts. The energy costs for the drives are so low that they are negligible in the economic considerations.

Particularly noteworthy is the implementation in the Hofburg Vienna, where a box-type window with four casements could not only be automated with only two motors for ventilative night cooling, but the solution also met the requirements of monument protection.

Using shading and windows as components for natural ventilation and cooling is nothing new and was already used in ancient times. Today these components can be automated and used to enhance their potential effects. Future technical developments are system kits with which (box) windows can be automated directly on site in an uncomplicated way with only little preparation effort. Self-learning algorithms automatically adapting to the existing environments and usage scenarios will also be future areas of interest. Finally, rising energy prices as well as legislative measures will make passive cooling concepts or hybrid concepts much more attractive.

Buildings can only be adapted to climate change through a bundle of measures. This research project has created the basis for cooling buildings passively and thus more energy-efficiently.

Project management

• Danube University Krems, Department for Building and Environment, Center for Climate Engineering
• Danube University Krems, Department for Health Sciences and Biomedicine, Center for Integrated Sensor Systems

Project or cooperation partners

• Forschung Burgenland GmbH
• Johann Gerstmann
• Woschitz Engineering ZT GmbH
• Fürstner RWA Systeme und Technik GmbH
• Zach Antriebe GmbH

DI Dr.techn. Daniela Trauninger
Dr.-Karl-Dorrek-Straße 30
A-3500 Krems
Tel.: +43 (2732) 893 - 2774
E-mail: daniela.trauninger@donau-uni.ac.at
Web: www.donau-uni.ac.at