A smart window for optimal ventilation with minimum heat loss

© Fraunhofer IBP

CLIMAWIN test windows in the climate simulator – Looking out from the room.

© Fraunhofer IBP

CLIMAWIN test windows in the climate simulator – Looking in from outside with sunlight simulator.

© Fraunhofer IBP

CLIMAWIN test windows in the climate simulator – Looking in from outside with sunlight simulator.


A project funded by the European Union’s Seventh Framework Programme (FP7) and bringing together partners in Denmark, Ireland, Portugal and Germany, has come up with a novel window system. Equipped with electronically controlled ventilation flaps, it can pre-warm the air you need to ventilate your rooms.

Picture a panel of double glazing and a panel of single glass separated by an air channel. Air needed for ventilation enters this channel through an opening at the bottom of the window frame, travels up between the panels and is then directed either into the room or back outside. On sunny winter days, for instance, this provides a source of pre-warmed air for ventilation.

In the summertime, air in the channel that would be too hot for effective ventilation is directed back outside and the additional air required for ventilation is fed directly into the room through a different opening. The flaps are controlled via an electronic module in the window frame that takes its cues from sensor data on CO2 levels, indoor humidity, and inside and outside temperatures. Some sensors are built into the window frame, while other, wireless sensors are distributed around the room. At the top of the window and doubling as a facing for the blind, a photovoltaic module provides the energy required to power the electronics as well as the blind itself. In this way, CLIMAWIN windows can replace those in existing buildings without the need for additional wiring.

Fraunhofer IBP’s role in the project was, where applicable, to determine the values for air permeability, water tightness under heavy rain, wind resistance, ventilation and acoustics in relation to the EN 14351-1 European product standard governing windows and doors.

In addition, the full window system was put through a battery of usability tests to examine flap performance, control algorithms, and the pre-warming of air under summer and winter conditions – with and without artificial sunlight and even factoring in the potential for the buildup of condensation. And to compile an energy-efficiency footprint, Fraunhofer IBP performed measurement tests on two types of window under summer and winter conditions at one of its test buildings in Holzkirchen near Munich.

These measurements were used to compile a TRNSYS® simulation model that was then applied to a mock-up building. This mock-up underwent two sets of calculations for locations in Germany, Denmark and Ireland; one using reference values from the German Energy Conservation Regulations (EnEV) and a comparison calculation based on a building featuring CLIMAWIN windows.

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Andreas Zegowitz

Fraunhofer Institute for Building Physics IBP
Nobelstr. 12
70569 Stuttgart, Germany

Phone +49 711 970-3333

Fax +49 711 970-3340