Eisenbahntechnische Rundschau 03/2013
StationGreen – a new standard for the passenger building of the future
Deutsche Bahn AG has launched its "StationGreen" programme, under which the first climate-neutral railway stations in Germany are being designed.
The first station, in Kerpen Horrem, is currently under construction and will be completed at the end of this year, while the StationGreen for Wittenberg is in the planning stage, with operation expected to start in 2015. This article explores the basic concept behind the pilot project in Horrem and sheds light on the various technologies applied for the resource-efficient and energy-saving construction of passenger buildings.
Deutsche Bahn AG's Group-internal architecture office began to develop innovative concepts for building new passenger buildings in 2009, under the working title "Stations for the Future". The starting point for this project was the conception of a building that would combine modern ecological standards with a high level of customer comfort. Such a combination aims to both protect the environment by reducing CO2 emissions and increase passenger satisfaction. The pilot project in Kerpen-Horrem will be a test bed for new technologies and the first CO2-neutral train station in Germany.
The StationGreen programme
The skeletal structure for the green buildings is based on modules measuring five by five metres, which can be combined according to the space available and usage requirements. The railway station in Horrem has a floor area of 620 square metres, making it a Category 4 passenger building visited by about 12,000 passengers a day. Functional features such as travel centre, waiting area, shops and adjoining spaces are laid out in such a way as to respond to the needs of users. The StationGreen concept can be easily adapted to suit passenger buildings of different sizes, from Category 4 up to Category 2 with as many as 24,000 people passing through each day.
StationGreen buildings are designed to let in a lot of light, by creating large glass fronts and using light-reflecting fixtures to dynamically manage both natural light and artificial light, blending them as needed throughout the day. The generous use of glass also ensures high transparency, aiding passengers' orientation. The model's facade is made up of around 52% glass, which in the winter months means that the sun's energy can be used to heat parts of the building. A large roof provides the shade required in summer and also space for a photovoltaic system and a solar thermal system.
The new passenger terminals therefore offer passengers a novel, innovative building concept that satisfies ecological needs and at the same time guarantees customer comfort. The clear structure and high transparency in the interior of these buildings facilitate orientation. A central, open-plan waiting area in the entrance hall provides a pleasant atmosphere for passengers changing services or waiting to depart. The station model is designed to allow mobility for all and meets the changing needs of people as demographic trends develop.
The building envelope is always made of materials that reflect regional characteristics. In Horrem the cladding will be in locally sourced slate, while for Wittenberg a clinker brick facade is planned. Through the use of materials from the surrounding region, a link is established to local architectural heritage and, as the materials do not have to be transported far, CO2 emissions are kept low.
Alongside the sustainable materials used in construction, another ecological factor is the geothermal system, with boreholes reaching 100 metres into the ground, that forms the physical heart of the StationGreen building. This, in combination with the photovoltaic system on the roof, allows the station to be self-sufficient when it comes to producing energy. Depending on the size of the roof surface, the PV system can lead to a zero-energy or even a plus-energy building standard being reached. At the same time, the building costs for a StationGreen with the dimensions described here are around 20% higher than those for a conventional passenger building without sustainability aspects.
In the first phase the concept is mainly being implemented in new, mid-sized passenger buildings, and in the second phase it will be applied to newbuilds and modernisation projects. The work that has been started on the first StationGreen signals the go-ahead for a new generation of resource-conscious, energy-efficient railway buildings for DB AG.
Methods and technologies
Natural and artificial light
The buildings are designed to make maximum use of natural light and provide transparency for good orientation. In addition to large windows, reflector elements redirect natural light into inner areas of the building. The lighting concept combines the use of daylight with energy-saving LED technology. At dusk a switch reacts to the fading light outside and blends in artificial light as needed. The installation of light fixtures fitted with LEDs in public areas lowers maintenance costs considerably.
View of the Wittenberg passenger building by night. Visibility and transparency aid passengers' orientation.
Photovoltaics and solar thermal energy
The building concept features a photovoltaic system that feeds energy back into the public electricity grid. On the roof, an area of 440 square metres is made available for thick-film PV modules that produce an output of 38.2 kW. The total output for a year is around 35,000 kWh. Heating via solar collectors is also utilised to generate hot water for facilities inside the building.
The StationGreen concept benefits from advances in technologies that harness the earth's heat, which make a considerable contribution to the building's positive energy balance. A heat pump system is set up that allows water to circulate via probes in the ground and delivers energy to heating appliances and underfloor heating. In order to achieve the highest performance possible from the pumping technique, a brine-to-water heat pump is installed. The geological inspection revealed that due to the soil conditions and the low water table, heat transfer of just 20 W per metre drilled can be achieved. Wells with a total depth of 1,000 metres are therefore required to cover the heating load of around 26 kW. The holes have been drilled in a row in front of the station building, spaced at a minimum distance of 6 metres, and connected to a heat pump. This pump will produce enough energy to satisfy the overall heating demand and, from its location in the mechanical room, distributes heat and cool air throughout the building.
The supporting structure for the roof is a ribbed construction in laminated veneer lumber. Prefabrication and large-scale formats lead to shorter assembly times at the building site. This is a decisive factor on construction projects where train services continue running, as is the case in Horrem. In addition, wood as a material has the advantage of being a fully renewable resource, as well as being extremely strong and therefore ideal for use in load-bearing structures. For the StationGreen in Horrem, a pillar-free hall with a waiting area has been designed to satisfy the demand for transparency and a large amount of natural light, which is easy to realise due to the large span width of the ribbed timber construction. The load-bearing structure is made up of a single-span beam with projections of various lengths at the sides. The supporting structure for the roof, meanwhile, rests on two steel legs, which are aligned with the upper edge of the load-bearing walls.
As well as accommodating the photovoltaic and solar thermal systems for processing the sun's energy, the roof will be planted with vegetation and rainwater will be collected for use in toilet flushing inside the building. The green areas will be planted with ecotypes of plants, grasses and herbs. Rainwater percolation on the roof and on the land surrounding the building reduces what is known as the heat island effect. In other words, the building and adjoining areas heat up to a lesser extent as surface water is not drained off into the wastewater system but allowed to evaporate locally. Aside from the better microclimate that this creates, it also has the advantage of lowering the operational costs associated with sealed surfaces.
In order to achieve annual primary energy consumption of 0 kWh, the total energy requirement calculated for the year is met by the output of the photovoltaic and thermal solar energy systems generated over the whole year. The total annual energy requirement includes energy for heating, cooling, ventilation, hot water and lighting, but not the energy required for operations and sales. For this second category, electricity produced from renewable sources is purchased.
Reserving space on the roof for planted water percolation areas alongside the photovoltaic system means the design of the building envelope is to be more energy-efficient than the reference values of the individual components specified in the Energy Conservation Regulations from 2009. For example, the ventilation system will involve as much waste heat recovery as is possible. Service water will be heated by solar thermal water heating technology, backed up by a heat pump connected to the brine circuit. The building will be heated via the electrically operated brine-to-water heat pump, which has a high level of efficiency due to deep drilling. Cooling for the building in summer can also be achieved using a brine recirculation system.
View of the interior of the passenger building in Wittenberg. Clear architectural lines, optimum use of natural light and visibility all the way to the platform are the central planning themes.
The StationGreen concept is the first in a series of train station buildings to be created with the holistic application of methods that protect environment, energy and climate, and is expected to become the standard for future passenger buildings. The pilot projects in Horrem and Wittenberg are the first prototypes, in which the use of sustainable technologies can be tested. The knowledge gained from implementing and operating these stations will be used to carry out future building projects and create the foundation for ecological construction in the renovation and building of railway stations.
Last modified: 14.03.2013