Heat and cold store © Geothermie Neubrandenburg GmbH

The energy generation and supply concept for the buildings of the German Bundestag provides an example of ecologically and economically combinable machinery, installations and transmission systems for energy generation and energy use.

1. Conceptual specifications for the energy supply of the new buildings of the German Bundestag
   Among other things, the specifications for the renovation of the Reichstag Building for the purposes of the German Bundestag included the demand for extensive use of renewable primary energy and for a high level of availability. At the same time, an energy concept was drawn up for the Parliament buildings in Berlin's Spreebogen district that put clear emphasis on decentralised energy generation.
2. Machinery used to implement the energy concept
   In both the Reichstag Building and the Paul Löbe Building, these specifications were realised by means of four diesel engines that drive power generators. Since, in accordance with the specifications of the energy concept, renewable primary energy was to be used in the Bundestag buildings, the decision was taken to use biodiesel as the fuel. To this end, standard engines were installed, some components of which had to be converted by the manufacturer to permit the use of biodiesel. The exhaust gas emitted by the diesel engines is cleaned in a complex emission control system - comprising particulate filters, reduction catalysts and downstream oxidation catalysts - to such an extent that the requirements specified in the German Technical Instructions on Air Quality Control (TA Luft) are significantly exceeded. The power generated in this way is supplemented by power from Berlin's public supply network.
   
   The heat from the engines and their emissions is sufficient for a minimum supply of heat for the buildings of the German Bundestag. To cover the heat requirement during the winter heating period, four hot-water boilers are available that were designed for peak-load supply and to act as a complete redundant system in the event of engine failure. During the summer, the surplus heat resulting from operation of the motor-driven cogeneration plants can be used to drive three absorption cooling machines. If neither heating nor cooling is needed in spring and autumn, the surplus heat is pumped into a geothermal storage system, from where it can be recovered as and when necessary.
   
   A regenerative system utilising the groundwater is also used with top priority for producing cold. Seven compression cooling machines are available at distributed locations for peak-load cold supply and as redundant systems.
3. Use of renewable energies and ecological building operation
   In keeping with the high ecological standard targeted, great importance is attached to the use of renewable primary energies.
4. • Biodiesel
     All engines and the boiler in the Reichstag Building run on biodiesel (the correct term is RME to DIN EN 14214). It is in keeping with the ecological objectives of the German Bundestag that the raw material is grown and processed in the close vicinity of Berlin. The raw material used is rape, from the seeds of which rape seed oil can be pressed. The biodiesel is produced in a biodiesel factory by adding methanol. All of the glycerol produced at the same time is sold to customers in the chemical industry.
     Apart from traces of unavoidable pollutants, a major proportion of the carbon dioxide generated by the combustion process of renewable raw materials, e.g. rape, is absorbed again in the region. Moreover, the use of agricultural produce also indirectly contributes to preserving jobs in rural areas.
   • Photovoltaics
     A total of roughly 3,600 m² of photovoltaic elements with different collector designs (some of which are heliotropic) are installed on the roofs of the Reichstag Building, the Paul Löbe Building and the Jakob Kaiser Building. The equipment was installed in the context of a demonstration programme of the Federal Ministry of Building. The power generated by the photovoltaic installations is fed entirely into the in-house network.
   • Heat generation and storage
     Surplus heat that is generated in the motor-driven cogeneration plants as a result of the combined generation of power and heat, and which is not needed either for heating in the buildings or for driving an absorption cooling machine in the prevailing weather conditions, is fed to an aquifer in front of the Reichstag Building via two boreholes reaching to a depth of roughly 300 m. To this end, the water stored in the porous rock of this stratum is pumped up through one borehole at its natural temperature of approx. 20 °C, heated by the surplus heat via heat exchangers in the basement of the Bundestag building, and pumped back down to the same depth through the second borehole, some 280 m away. Water with a maximum temperature of 60 °C is pressed into the rock at a maximum pumping capacity of 100 m³/h and pumped back up during the next heating period at temperatures starting in the region of 55 °C. The feed temperature declines as removal progresses, until economically viable tapping of the heat reaches its limits at approx. 30 °C.
   • Cold production and storage
     The top priority in connection with cold production is to store ambient cold in winter, which is dissipated into the groundwater via heat exchangers. This process is concluded at the end of the cold winter period, after which the cold water is tapped by reversing the direction of flow at the start of early summer, initially being drawn from the respective cold well at approx. 6 °C. Depending on the intensity of use, this temperature rises up to the natural temperature of 11 °C in the course of the summer. If the Bundestag buildings simultaneously require more cold than can be taken from the cold storage wells, this cold is initially generated by conventional cooling machines. If the demand increases even further, and if prolonged demand is expected on the basis of the summer temperatures, the three absorption cooling machines are operated using the waste heat from the motor-driven cogeneration plants.
5. Technical equipment
   It is part of the concept of ecologically oriented and need-based generation of power, heat and cold that these types of energy are used sparingly in the technical equipment of the buildings. For example, ventilation systems equipped with fans requiring little drive power were designed to this end. In many areas, the circuitry is engineered to give priority to natural ventilation, rather than air-conditioning by means of ventilation systems, if the indoor and outdoor temperatures allow. In addition, passive and active shading, together with thermal insulation of walls and windows, makes a decisive contribution to reducing the input of outside heat into the conference rooms and offices. Lighting is provided by luminaires fitted with high-efficiency lamps, which are switched on and off via a light management system as required.
6. Optimised use of energies in the energy network
   Alongside the resource-conserving use of primary energies, the need-oriented generation of heat, cold and power is also part of the ecological concept. For example, there is the possibility of generating these forms of energy in different areas of the Bundestag buildings and transporting them to other buildings in accordance with requirements. There is a connecting network for 10 kV electricity with transformers in each building for this purpose. Similarly, the generated heat can be pumped in both directions between the buildings at a temperature level of 110 °C. All buildings participate in cold storage, and some can also transport the cold water produced in the cooling machines to the neighbouring building as and when needed. This energy network is controlled by a master automation system that permits manual intervention.
   
   As the Federal Chancellery also has a motor-driven cogeneration plant, a connecting line to the heat store of the Bundestag energy system has been installed in order to avoid the need for a separate heat storage system. It can absorb surplus heat and also pass it back if necessary.
7. Operating experience
   Energy generating operations were constantly improved in the first few years of operation. The cold store works highly satisfactorily. Roughly 60% of the surplus heat resulting from operation of the motor-driven cogeneration plants and saved in the heat store can be recovered. Scientific studies are carried out to monitor the operation of the cold and heat stores.
8. Transferability of the energy concept
   The energy generation system described for the Bundestag buildings would appear to be transferable to other buildings and consumers only if similar consumption characteristics are present in terms of the simultaneous demand for heat and power or cold and power. Also, underground storage in front of the Reichstag Building is only possible because of the favourable geological conditions and can therefore not be expected to work so efficiently everywhere in Germany.