Environmental Agency

German Federal Environment Agency in Dessau

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

Photo: © Dirk Wilhelmi

A municipal building with a complex architecture and a high level of energy efficiency

The German Federal Environment Agency, which has been based in Dessau since 2005, employs more than 750 employees who are dedicated to the protection of water, soil and air by collecting and publishing environmental data, providing scientific support to the Federal Ministry for the Environment, assisting in the development of environmental laws and participating in their implementation.

A modern office building sets standards in several ways: architecturally thoughtful design, energy efficiency and renewable energy sources make this building a role model. The unusual layout of the four-storey building, designed by the world-famous Berlin architectural bureau "Sauerbruch Hutton Architekten", forms an elongated loop. The resulting courtyard has a glass roof and is used for passive use of solar energy. The highly insulated exterior exceeds the requirements of the Thermal Insulation Ordinance (in force at the design stage of this building) by 50 percent and the requirements of the then Energy Saving Ordinance (EnEV) by more than 30 percent.

The design engineers were tasked with ensuring that at least 15 percent of the total energy demand was met by renewable energy sources. The Berlin-based engineering firm Zibell, Willner & Partner has developed a special energy concept: heating by district heating from a landfill gas thermal power plant operated by Stadtwerke Dessau. A mechanical ventilation system with heat recovery was responsible for the ventilation of the interior of the building. In this system, the supply air is heated in winter and cooled in summer using a geothermal collector with a total length of 4800 meters. Electricity is supplied by a photovoltaic system with an area of 228 square meters. All rooms with specific cooling loads, in particular the sensitive server room, are cooled by an adsorption refrigeration unit that uses heat to generate cooling energy. The planning and implementation of this innovative energy system was overseen by the Federal Commissioner for Energy, Dr. Uwe Römmling from the Institute for Building Conservation and Modernization.

Vitosol 200-T tubular manifolds. Photo: © Dirk Wilhelmi

AHI-Carrier solar thermal system for efficient cooling and heating

The adsorption refrigeration unit uses water as the refrigerant and silica gel as the solid binder. In a closed loop, water evaporates at a pressure of 10 mbar at temperatures up to 5 °C. In the process, heat is extracted from the cooling water entering the cooling surfaces of the rooms. The vapor enters the adsorber chamber, where it is adsorbed by silica gel. To drive the refrigeration unit, heat is applied, which pushes the steam in the silica gel back to the outside. The steam is then condensed in a separate chamber. The condensate is then sprayed back into the evaporator, where it evaporates again under negative pressure.

The adsorption refrigeration unit receives the necessary energy from one of the largest solar thermal systems in Germany. Divided into three large collector arrays, the 115 Vitosol 200-T vacuum tube collectors from AHI-Carrier produce around 140 MWh of energy per year. Absorbers with a sol-titanium coating absorb a particularly large amount of solar energy, thus ensuring a high energy yield. The total area of the collector is 345 square meters. A total of 3,450 individual tubes were installed on the flat roof by employees of Friedrich Heizungsbau GmbH from Hohenseefeld.

The resulting solar energy is stored in three buffer cylinders for heating water, each of which holds 7500 liters. The solar thermal system and buffer cylinders serve a dual purpose: in spring/autumn and winter, the solar energy that is not needed for cooling can be used in the heating system.

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