A smart window for optimal ventilation with minimum heat loss
A project funded by the European Union’s Seventh Framework Programme (FP7) involving 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 needed to ventilate rooms.
Imagine a panel of double glazing and a panel of single glass separated by an air channel. The air needed for ventilation enters this channel via an opening at the base of the window frame, travels up between the panels and is then guided either into the room or back outside. On winter days when the sun is shining, for instance, this provides a source of pre-warmed air for ventilation.
In the summertime, the air in the channel would be too hot for effective ventilation and is therefore directed back outside; the air required for ventilation is fed directly into the room via a different opening. The flaps required for this are controlled by an electronic module in the window frame that takes its cue from sensor data on CO2 levels, indoor humidity, and indoor and outdoor 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 a blind, a photovoltaic module provides the energy required to power the electronics as well as the blind itself. In this way, CLIMAWIN windows can be used to replace existing ones in buildings without the need for additional wiring.
Fraunhofer IBP’s role in the project was to determine the values for air permeability, water tightness on exposure to heavy rain, wind resistance, ventilation, and acoustics in accordance with the EN 14351-1 European product standard governing windows and doors.
In addition, the complete window system was put through a comprehensive series of usability tests to study flap performance, control algorithms, and the extent to which the air is pre-warmed under summer and winter conditions – with and without artificial sunlight and even factoring in the potential build-up of condensation. To measure the energy efficiency of the system, Fraunhofer IBP performed tests on two types of windows 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. The mock-up underwent two sets of calculations for locations in Germany, Denmark, and Ireland - once using reference values from the German Energy Conservation Regulations EnEV and once with CLIMAWIN windows installed in the building for locations in Germany, Denmark and Ireland.