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District heating

German Federal Environmental Agency in Dessau

For the municipal building in Dessau, the focus was on high energy efficiency. The architects and design engineers opted for one of Germany's largest solar thermal systems with 115 Vitosol 200-T tube collectors.

Photo: © Dirk Wilhelmy

Municipal building with sophisticated architecture and high levels of energy efficiency

The German Federal Environment Agency, which has been based in Dessau since 2005, employs more than 750  people who work here to protect water, soil and air by collecting and publishing environmental data, providing scientific support to the Federal Ministry for the Environment, helping to draft environmental laws and participating in their enforcement.

The modern administrative building sets standards in several respects: architecturally sophisticated in design, constructed with energy efficiency in mind and supplied with renewable energies, this building is a model for others to follow. The unusual floor plan of the four-storey building designed by internationally renowned Berlin architectural firm "Sauerbruch Hutton Architekten" forms an elongated loop. The resulting inner courtyard has a glass roof and is used for passive solar energy use. The highly insulated exterior surpasses the requirements of the Heat Insulation Ordinance (in force at the design stage for this building) by 50 percent and the requirements of the German Energy Saving Ordinance (EnEV) in force at that time by more than 30 percent.  

The design engineers were set the task of ensuring that at least 15 percent of the total energy demand is covered by renewable energies. The engineering firm Zibell, Willner & Partner in Berlin consequently developed a special energy concept: heating by means of district heating from a landfill gas CHP unit operated by Stadtwerke Dessau. A mechanical ventilation system with heat recovery was responsible for ventilating the interior of the building. In this system, the supply air is warmed in winter and cooled in summer by a geothermal collector with a total length of 4800  metres. Electricity is supplied by a 228 square metre photovoltaic system. Any rooms with specific cooling loads, particularly the sensitive server room, are cooled by an adsorption refrigeration unit that uses heat to generate cooling energy. The planning and execution of this innovative energy supply system was overseen by the Federal Energy Commissioner, Dr. Uwe Röömmling of the Institute for the Preservation and Modernisation of Buildings.  

Vitosol 200-T tube collectors. Photo: © Dirk Wilhelmy

Viessmann solar thermal system for efficient cooling and heating

The adsorption refrigeration unit uses water as a refrigerant and silica gel as a solid binding agent. In a closed circuit, the water evaporates at a pressure of 10  mbar from temperatures as low as 5  °C. In the process, heat is extracted from the cooling water flowing into the cooling surfaces of the rooms. The vapour arrives in the adsorber chamber where it is adsorbed by the silica gel. To drive the refrigeration unit heat is now supplied which expels the vapour in the silica gel back out. The vapour then condenses in a separate chamber. The condensate is subsequently sprayed back into the evaporator, where it evaporates again under negative pressure.  

The adsorption refrigeration unit receives the required drive energy from one of the largest solar thermal systems in Germany. Split into three large collector arrays, 115 Vitosol 200-T vacuum tube collectors from Viessmann yield around 140 MWh of energy per year. The sol-titanium-coated absorbers absorb a particularly large amount of solar energy, thus ensuring a high energy yield. The overall collector area is 345 square metres. A total of 3450 individual tubes were installed on the flat roof by the employees of Friedrich Heizungsbau GmbH from Hohenseefeld.

The solar energy obtained is stored in three heating water buffer cylinders, each with a capacity of 7500 litres. The solar thermal system and buffer cylinders serve a dual purpose: in spring/autumn and in winter, the solar energy that is not needed for cooling can be fed into the heating system.  

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