Article by Oscar Hernandez. Published in the REHVA Journal, May 2011. Elithis Tower in Dijon in France, provides strong evidence that net zero energy office buildings are achievable in near future. The building, which was designed by Arte Charpentier Architects, also produces six times fewer greenhouse gas emissions than traditional office structures. The Elithis tower is composed of 9 levels and 1 technical level (HVAC system). The height is 33.5 meters. 4 levels are occupied by Elithis engineering, and the others by the Ademe (Departmental Agency of Energy Management), radiological services, a restaurant and other civil engineer companies. The average occupancy is 15 m2/person.
The building has a central core made of concrete and the facades are made of wood and recyclable insulation (cellulose wadding). The surface fenestration is about 75% of the facades. The windows are double-glazed with an argon air space. Window U-Value is 1.1 W/(m².K) with g-value 0.4. The thermal mass of the building can be considered as medium because the central core only is the exposed concrete. Exterior wall U-value is 0.32 W/(m².K), base floor U-value is 0.39
W/(m².K) and roof U-value is 0.22 W/(m².K).
The design concept focuses on compact building shape, passive solar shading, lighting system, heating & cooling system & distribution, water management and ventilation strategy. The building is ventilated by mechanical supply and exhaust system with heat recovery controlled by the BEM system in order to comply with the French ventilations standards codes (25m³/h per person in offices). The ventilation system is operated in three modes depending on the season.
For typical heating season operation (outdoor temperature higher than 0°C), operation with controlled heat recovery is used to heat up supply air with heat recovered from extract air. Heat recovery is controlled/bypassed so that supply air temperature is between of 16 to 18°C. The full heat recovery operation is used for extremely cold or warm outside conditions (less than of 0°C in winter or higher than 26°C in summer).
In the mid-seasons (spring and fall) and summer operation, the triple flow mixed mode system which is an Elithis innovation, is used. It gives the possibility for ventilative cooling with fresh air intakes and central atrium exhaust ventilation in order to cool the building. 32 air valves in facades per level are used to have additional intake air. In this mode, air handling units are operated together with intake air from facades and atrium low pressure exhaust fans.
The third operation mode is the free cooling. Air handling units are stopped and atrium exhaust used in order to ventilate the building in night summer time. In this mode, the building can be ventilated with low pressure central atrium exhaust ventilation. The 32 air valves are opened in order to ventilate the building with two or three times higher flow rate than the design air flow rate.
Published in the European Energy Efficient Magasine, July / August 2009, European Energy Review.
The Elithis Tower in Dijon in France has been heralded as ’the most sober building in the world’. Even more striking than the building is its visionary builder, Thierry Bièvre. “Energy savings are driven by brainpower rather than by technology.” His aim was to combine aesthetics, urban integration, comfort, and energy efficiency in an environmentally friendly building at the same cost as a traditional building. So the specifications had to be very strict. “Brainpower was used to compensate for any funds required over and above the cost of a traditional building.” The Elithis Tower, the result of his efforts, started in 2006 and completed in April 2009, is above all sober. Energy efficiency takes priority over using renewable energy. “We didn’t draw the building, we wrote it down for the architect.”