Energon: 6000 m² passive office building in Ulm, Germany

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1 Energon: 6000 m² passive office building in Ulm, Germany I2 Barbara Faigle oehler faigle archkom, Germany ABSTRACT Energon is the biggest office building in Europe in a passive house standard. On Energon we show that an efficient office building today can be a passive house and compete with standard building designs. From the beginning the design was developed in strong connection with civil and structural engineers. We wanted to make sure to get the best results for the building and as well for the technical requirements in the building. At the end it is a passive house with all its advantages, but the user does not realize a difference, apart that it is more comfortable as a normal building. It is a simple shaped 4-storey building. The ground floor is used as a multipurpose space; the upper floors are flexible office spaces. In the center is a glass-covered atrium, used as circulation space and to bring daylight into the inner office spaces. For heating and cooling we use floor slab activation. The system heats with a maximum temperature of 24 C and cools with a minimum temperature of 19 C. This is possible because of the good insulation and the air tightness of the building. We need less heating in winter and less cooling in summer. To ventilate the building we bring supply air into the atrium and from there to the offices. The structure is a concrete frame building with prefabricated curtain wall system. Energon as a passive house is a benefit for the user as well as for the owner. The building is sustainable, efficient and comfortable. The construction cost for Energon is in the same range as typical office buildings in Germany. 1

2 1 INTRODUCTION Proceedings Passiefhuis-Symposium 2005 Energon is the biggest office building in Europe meeting passive house standard. The project started in fall 2000 as an invited competition. The client asked the design teams to create a passive house, even though he was not completely convinced by the idea at the time. So our job was to create a leading key project as a passive house using the highest available energy efficient technical solution. For the client we wanted to create a unique building, comfortable to use, energy efficient and within a budget competitive with standard office buildings. Together with a passive house experienced team of engineers we were able to convince the client with our competition entry. In Summer 2001 we started with the construction on site and in October 2002 the project was completely finished. The client celebrated the opening as a large PR-event for his company Figure 1 He used the building exactly the way we had designed it for. The 5-storey high atrium was perfect for the light show, the ground floor of the atrium housed all the guests and on the two bridges over the atrium on the first floor, a modern dance performance took place, followed by band entertaining the guests. The building is located in an area, where the city of Ulm encourages energy efficient buildings. The freestanding building is located at the edge of the development on a site slightly sloped southwards. There are a lot of design keys to observe, while developing such a large passive house building. To reach the passive house standard, it is important to integrate the different kinds of engineers (i.e. mechanical, structural and physical) into the project from the beginning. 2

3 2 DESIGN SCHEME Proceedings Passiefhuis-Symposium 2005 According to the site and urban surrounding we developed a freestanding 5-storey building with a simple shape. In perspective it looks like a rotary piston engine. The outer ring houses the office space. In the center there is the glass-covered 5-storey atrium. This space is also used as a huge fresh air supply duct for the offices. The upper 4 floors are typical office spaces. Parts of the offices are located facing to the outside of the building, parts of them to the atrium. The advantage is to have different daylight quality in each workspace. The typical office floors can be divided in flexible sized units, according to the requirements of the different users. On two corners of the building the required escape stairs are located. In the third corner is the installation duct for exhaust air leading up to the roof. In the center is the atrium, which houses the spiral staircase and two panoramic glass-lifts. The atrium on the ground floor functions as a central marketplace. It is used for performances, concerts, exhibitions, staff meetings, as a café and as an informal meeting place. Perforated panels integrated in balustrades and suspended ceilings offer perfect acoustic conditions in the atrium. The atrium is covered with a sloped glass roof. To prevent overheating there are ventilation openings and the translucent foil between the glass sheets serve as sun shading. The slope of the site helps us to separate different requirements of the building access, as building entrance, parking and delivery. The main entrance on the north is on the first level. The entrance to the underground parking and delivery is one level lower, on the northeast corner. The garden level is a multipurpose space, with meeting rooms, a restaurant, kitchen area, storage and engineering rooms. The restaurant and meeting rooms on the southeast and southwest façade, opens to the outside on wooden decks overlooking the water pond and the garden. The underground parking garage, in the back of the building on the ground floor, is the naturally ventilated. The exhaust air plant sits in the roof. 3

4 Figure 2 3 CONSTRUCTION The entire building is grounded on pile foundations. Underneath the concrete floor slab is 30 cm thick insulation. The efficient concrete frame structure has flat bearer free slabs and round columns. The column span is determined by the typical office size and internal circulation hallway. The floor height is 3,24 meters and the clear room height of the offices is 2,50 meter. Suspended ceilings are only in hallways and small parts of the offices. They house the exhaust ducts and lighting. The 25 cm thick floor slabs are flat and bearer free. The floor built up is 8,5 cm. The exterior wall system of the 4 office floors is a prefabricated curtain wall system. We developed it together with engineers especially for that project. The timber boxes are filled with 30 cm insulation. Each box on each level has the same rectangular size, although the building shape is curved. Only the edges are special elements. The prefabrication of the façade minimizes the construction time on site, and keeps tolerances to a minimum. The steel walkways in front of the façade serve for maintenance of the façade and as emergency exits. 4

5 The typical offices have closed balustrades and normal windows. They can be opened for natural ventilation by each user individually. They have triple glazing with highly insulated frames. All the windows and the glass façade have outside sun shading. On each of the three building sides there is a vertical glazed section from floor to ceiling. Behind this glass front the meeting points and the access to the atrium are located. The garden level walls are brick with a 30 cm outside insulation, alternating with the glass fronts of the restaurant and meeting rooms. The roof is a concrete slab, with a slightly sloped wood structure. It is insulated with blown in paper insulation. Integrated in the roof sheeting are the solar panels. The solar panels have a capacity of 15 kwp. Most of the interior walls are lightweight drywalls, to keep the floor plans flexible for future user requirements. The glass roof over the atrium is a suspended steel structure, with doubleglazing and standard frames. prefabricated curtain wall system office floors U-Value=0,13 W/m²K brick + 30 cm insulation ground floor U-Value=0,11 W/m²K typical office windows office floors U-Value=0,84 W/m²K ground floor slab U-Value=0,22 W/m²K roof U-Value=0,12 W/m²K glass roof atrium U-Value=1,80 W/m²K 4 HEATING AND COOLING The challenge of such a large passive house building is not, to keep it warm in winter; it is to keep it comfortably cool in summer. Today there is a computer for every workspace and on each of the office floors a lot of other technical equipment, like printers, scanners and copy machines. They all work as little heating units, which heat up our building constantly. This heating load has to be taken care of, in winter as well as in summer The insulation and the airtight level are continuously wrapped around the building according to the passive house requirements. With this measurement the heat loss in winter is kept to a minimum. That means a minimum heat demand in wintertime to keep the temperature comfortable for the users. The small required heat demand of the building 5

6 is covered from the heat recovery of the exhaust air and by district heating. It is a bigger challenge to keep the building comfortably cool in summer. To achieve that, there are only floor to ceiling glass facades in very small areas. The typical office has a closed balustrade and windows. The louvers of the outside shading blinds can be turned in different positions. That avoids direct sunlight and heat to get into the building. It also gives the user an individual option to regulate the daylight, which comes into the building to work without electric light. On Energon it is difficult to locate the south side of the building by plan or elevation. Here we made the experience: the larger a building is, the less important is the solar orientation for the passive house standard. 5 FLOOR SLAB ACTIVATION There are 40 boreholes around the building, 100-meter deep each. In winter they preheat the intake air and they preheat the water for the floor slab activation. In summer they cool the entire system. For heating and cooling the building, we use the large uncovered surfaces of the floor slab for floor slab activation. The large floor slab areas function like huge radiators. The water pipes for the floor slab activation are in the concrete floor slabs, together with the air ducts and all the required reinforcement. The system heats with a maximum temperature of 24 C and cools with a minimum temperature of 19 C. This is possible because of the good insulation and the air tightness of the building. Therefore less energy for heating in winter and for cooling in summer is needed. 6 VENTILATION CONCEPT OF THE BUILDING The fresh air intake is integrated in the garden design, with three stainless steel pipes. In an underground duct the air is taken to the supply air plant and from there to the atrium. The atrium space functions as a big supply air duct. From there the supply air is directed into the individual office spaces. The offices facing the atrium get their fresh air directly by opening the windows or through permanent ventilation openings integrated in the 6

7 façade to the atrium. The air supply ducts for the outer offices run from the atrium in every concrete floor slabs to the office space on the outside of the building. The exhaust air ducts are located in the suspended ceilings above the hallways. From there the exhaust air goes up to the roof, where the exhaust air plant with heat recovery sits. Using this system we avoid duct crossings on the ceiling, minimizing the required floor height of the building. Generally each office is mechanically ventilated, however there is also the option to ventilate each room individually, by simply opening the window. The multi purpose rooms on the ground floor have separated ventilation. For the meeting rooms with a high attendance per m² a higher ventilation is required. In the restaurant and kitchen we have to separate the food odors, from the atrium and other areas. For these special purpose spaces a specifically designed separate air supply ensuring sufficient ventilation is in place. 7 PASSIVEHOUSE STANDARD: BENEFIT FOR THE ENVIRONMENT, THE OCCUPANT AND FOR THE OWNER The tools, passive and active, allow us to reach a maximum confidence for the owner as well as for the users. Energon as a passive house is a benefit for all. The building is sustainable, efficient and comfortable. The benefit for the environment is easily expressed in the following numbers: The building needs 75% less energy for heating and cooling than a standard office building. This means the annual CO2 reduction for the building with the solar panels is 2670 tons. The emission is zero, because of the solar collector on the roof and a separate one on a separate parking garage. Most materials used for he building are recyclable like timber for the facades. We tried to avoid using building parts of composite materials, which are not recyclable. The rainwater is collected on the roof and in the site and used in the water pond in the garden, which also functions as a retention basin. The benefit for the user is a comfortable building, simply to use, providing a comfortable and healthy climate in winter and summer, good air quality, 7

8 Figure 3 pollen free, daylight and dazzle-free workspaces low rent und low utility charges. The benefit for the owner is: similar construction cost compared to a standard office building, but better quality, good real estate value, low utility charge in the long run, government subsidies, prestigious key project, highly technical and efficient building standard. In numbers: The building cost was 312 /m³ per gross volume (DIN 276, / excluding furniture, landscaping, cost for the site. Building only.). An average office building in Germany runs from 315 to 384 /m³. The utility cost for heating, cooling, ventilation, air humidification and warm water is 34 / workstation each year. 8 FACTS AND SUMMARY Workspace capacity of the building: Building gross volume: m³ Net floor area: m² 420 workspaces 8

9 On energon we show that an efficient office building today can be a passive house, and can compete with standard building designs. However, it is important, from the early project phase of the design on, to form a strong experienced team together with the different kinds of engineers, and to use all the tools we have as planers to create an efficient sustainable building. It clearly shows we can compete with standard office buildings. At the end we even have a better building, offering higher technical standards for less money. ACKNOWLEDGEMENT AND REFERENCES Planning team: Architects: oehler faigle archkom, solar architektur, Stefan Oehler, Barbara Faigle Structural engineer: Prof. Lachenmann, Vaihingen/ Enz Germany Mechanical engineers + energy concept: ebök Tübingen Germany oehler faigle archkom solar architektur Barbara Faigle melanchthonstrasse 10 D bretten/ germany Fon + 49 (0) Fax + 49 (0) Info@archkom.de 9