Two Examples for Corporate Identity by intelligent building design Economical and publicity aspects to build a sustainable low energy office building Matthias Schuler, Prof. Dr. Thomas Lechner TRANSSOLAR Energietechnik GmbH, Curiestraße 2, 70563 Stuttgart Tel. +49 711 67976 0: Fax: +49 711 67976 11 Abstract The are many reasons for a client or investor to ask for design brief for a sustainable low-energy building and these differ depending on the project. The experiences of two completed projects through design, construction and 2 or 3 years occupation show economical and publicity benefits not typically associated with these types of buildings. Both projects were designed within interdisciplinary design teams consisting of architects, construction engineers, HVAC (heating-ventilation-air conditioning) engineers and the climate-engineers. The experiences of both projects show that an intelligent integrated approach to building design can lead to low-energy buildings with reduced initial investment and running cost as well enhanced architecture. The table 1 shows the comparison between different energy and ventilation concepts for office buildings showing both running costs in DM/ and the initial investment in DM/m 2. In addition the real values for the project DATAPEC are listed to show the benefits of an integrated design approach. Introduction The two examples, which will be described in the following pages, are medium sized office buildings (3.000 7.500 m 2 total area ). In both cases the building client was not an anonymous speculative investor but the final user of at least part of the building. They were therefore concerned on one hand that the initial capital costs of the construction should be kept as low as possible whilst on the other hand a concern with reducing the running costs of the building opened up the possibility of additional investment. The clients for both project were hi-tech communications companies (DATAPEC and WAT) and participated fully in the design process alongside the design team. This team of architects, construction engineers, climate engineers, HVAC engineers and building physicists developed the two building concepts depending on their different locations and final use. The brief from both companies for the new buildings was to provide a comfortable working environment with reduced running and operating costs as well as a visual expression representing the innovative nature of their businesses. The following pages will describe the two projects by aims, concepts, realisation, occupation and hopes to document the differing ways of developing a sustainable low-energy building.
Cost comparison of the different concepts Running costs for Artificial lighting & air conditioning Artificial lighting & mechanical ventilation (free cooling) Natural daylighting & ventilation artificial lighting 0.83 DM/m²/ 0.83 DM/m²/ 0.42 DM/m²/ DATAPEC Headquarters 1996 (completed) 0.23 DM/m²/ mechanical 0.93 DM/m²/ 0.46 DM/m²/ - 0.10 DM/m²/ ventilation (fan power) chiller plant 0.90 DM/m²/ - - - heating 0.33 DM/m²/ 0.33 DM/m²/ 0.47 DM/m²/ Maintenance cost of HVAC System Estimated ly running cost for HVAC and artificial lighting estimated investment Table 1 0.77 DM/m²/ 0.40 DM/m²/ 0.12 DM/m²/ 3.76 DM/m² per 2.02 DM/m² per 1.01 DM/m² per 0.20 DM/m²/ 0.13 DM/m²/ 0.66 DM/m² per 460 DM/m² 240 DM/m² 70 DM/m² 92.70 DM/m² DATAPEC Headquarters, Gniebel Design team: Architects: Structural planner: HVAC: Building physic: Climate concept: Kauffmann Theilig und Partner, Stuttgart. Project leader: W.Kergaßner H. Steinhilber, Pfefferkorn und Partner Engineering office Schreiber, Ulm Engineering office Horstmann, Altensteig TRANSSOLAR Energietechnik GmbH, Stuttgart Building data: Begin of planning: June 93 Begin of on: December93 Occupation: 2/95 Location Height: 415 m Gniebel, BW volume (BRI): 21.000 m³ Total area (BGF): 7.500 m² Heated (HNF): 5.600 m Building costs Total: 17.000.000 DM (cost groups 1 7, DIN 276) per m² (total) 2.270 DM/m² AIMS The primary goal in the development of DATAPEC's new office building was to create a work place with optimized thermal and visual comfort and to reduce the investment costs for ventilation and cooling systems. The concept design of the building was to use naturally occurring phenomena along with the structure to condition the ventilation air and thus remove the need for air-conditioning. The central atrium was designed to function as "a center providing freshness and coolness in summer.
The design team consisting of architect, structural engineer, HVAC engineer, building physicist and climate engineer were charged with realising these aims. The climate engineer - a branch of engineering that has developed only recently - gives advice in the field of construction wherever the interaction between the external and internal environment plays a role and utilizes new design tools such as computer simulation programs in order to achieve these goals. This interdisciplinary activity is very important since today building components often have to perform multiple functions such loadbearing structures which are also used for ventilation air and to provide fabric cooling PROBLEMS In reaction to the design brief for this project consideration was made that many of the work places at DATAPEC (a company distributing hardware and software for large administration offices) would have at least 2 computers. Therefore problems with artificial lighting and glare, as well as internal heat gains of nearly 300 Watts per work place had to be considered in the design. A survey in the client's existing office showed that most employees felt comfortable with a lighting level of around 100 Lux, which was achieved by taping opaque foil onto the windows. 30 Lux was felt to be even more comfortable, as opposed to the standard regulations for work places which demand 300-500 Lux at desk level. Commonly, buildings that have to use artificial light in the day have high internal heat gains, which leads to overheating, requiring the installation of a cooling system. In addition, the room depths (8-12 m) prohibit the use of single-sided window ventilation (according to the ventilation regulations).
BASIC DESIGN CONCEPT The overall design philosophy was to give each building component multiple functions. For example: - atrium: air and light duct, offering a buffer zone between internal and external climate - floor: air duct and thermal storage as well as a load-bearing structure - facade: passive shading device and recreation area Compare the attached system sketch for the summer function on the next page. BUILDING SHAPE The circular design of the atrium and facade have several advantages to the environmental and structural design of the building. The external facade area is minimized. This has two advantages: lower construction costs and lower heat loss. Also the glazed area is reduced compared with conventional building designs (structural glazing etc.), again this has two advantages: lower heat losses in winter and reduced gains in summer whilst maintaining the advantages of natural daylight. DAYLIGHTING Deep balconies and the overhanging roof are used as fixed sun shading devices and prevent direct rays of daylight entering into the work places. Therefore the problem of glare from surfaces is reduced and a strong contrasts can also be avoided which are important aspects for computer work areas. At the same time the structure with the core atrium provides day-lighting on both sides i.e. indirect sunshine through the atrium giving a more uniform illumination level. BUILDING SERVICES A localized air supply is necessary for room depths of up to 12 m. This is done by using distribution elements for fresh air which are placed below the fitted carpet. The ceilings have a thickness of 30 cm in order to deal with the structural loads and 10 cm diameter ducts were put inserted into the neutral zone of the ceilings. This method has no negative influence on the structural behavior. These ducts are used - within some limits - as ducts for fresh air and electric services. They are positioned nearly radial round the atrium.
AIR VENTILATON Fresh air comes in through a concrete earth-duct below ground level. The air will be pre-cooled in summer and preheated in winter by the thermal mass of the earth. After passing through the concrete duct and the heat-exchanger of the heat-recovery system the air is blown by a fan into the central atrium. The atrium serves as manifold for the ceiling ventilation ducts. These smaller ducts suck the air from the atrium and blow it through the carpet displacement grills into the office rooms. After use the exhaust air is collected below the ceiling and extracted by exhaust fans via the heat-recovery system. After the useful heat is removed the air is expelled at roof level. PREDESIGN WITH COMPUTER TOOLS Parallel computer simulations were conducted to model the expected thermal behavior of the building. It is essential to calculate the storage of heat within the building structure making it necessary to carry out dynamic building load simulations. In this project, the program package TRNSYS [1] was used because it allows the user to specify individual system components such as the fan and the heatrecovery unit for the earth-duct along side a dynamic building simulation. The engineer can also define any control strategy for shading, lighting and ventilation up including flushing the building fabric with cool nighttime air. The profiles of the various air temperatures in the rooms of the building allow an investigation into the success of the proposed concept. From this information guidelines for the architect and HVAC engineer can be obtained. The structural engineer can also predict the influence of the temperature changes on the various structures. Daylight simulations were carried out with the program package ADELINE which interfaces with the thermal simulation package TRNSYS. The heat gains from internal lighting required can be considered and strategies for minimizing internal gains can be validated. The resulting heating and cooling loads indicate to the client the future operating costs and allow a description of the economics of different building components (like glazing, insulation, ventilation). FINE-TUNING OF THE BUILDING DESIGN After approving the draft building concept all members of the design team had to draw consequences for their own area of expertise. The structural engineer, for instance, had to integrate the ventilation ducts into the floors, i.e. into the iron support structure. The HVAC engineer has to redesign the ventilation system etc. As all the designers involved in the project have to consider the economic and physical implications of their decisions this process becomes one of optimization. The minimization of the external surfaces and the insulation level of opaque walls (14 cm mineral wool), roof (16 cm foam-glass) and transparent building parts (windows U-value 1,3 W/m²K) result in a heating load of 25 kwh/m²a. This low value (30% below the actual regulation) is achieved by the building envelope, heat recovery of the exhausted air and to a smaller extent by increased internal gains. The heating period of the office building of DATAPEC is reduced to 6 s. The concept of double-use (building parts are used for air conducting) has a significant effect on the costs associated with the ventilation system (see economic consequences). REALIZATION During the construction phase a lot of questions about the new system components had to be answered, since many of the components were unknown to the contractors. Thus, after conclusion of the construction phase, the new system components (underground earth-duct, integrated air ducts) worked very well. At the commissioning phase difficulties occurred only with well-known components.
ECONOMICS For HVAC the first cost estimate excluding cooling was 1.100.000 DM. The final total costs were 700.000 DM. However changes of the structural construction, underground air duct, imbedded ceiling ducts and increased planning requirements reduced the total investment savings for the client to 250.000 DM. Although the investment costs were reduced, the design team's salary was not reduced as would usually be demanded by engineering regulations. This was only possible since it was agreed before the start of the design phase that the planning engineer would benefit if the investment costs were below standard level. Ultimately the investment costs for heating, venting and air-conditioning were only 5% of the total construction costs. In addition the client benefits per year from reduced operating costs of the building are now about 20.000 DM (at the actual energy price level) ENERGY CONSUMPTION During the occupation of the building the energy demand for heating, lighting and electrical applications has been monitored and compared to the design values. Design measured Heating 25 kwh/m²a 30 kwh/m²a Lighting 9 kwh/m²a 11 kwh/m²a Other electricity 50 kwh/m²a 60 kwh/m²a ACTUAL BUILDING PERFORMANCE The offices are now fully operational with greater internal heat gains than in the brief. Reduced atrium temperatures have lead to thermal comfort problems due to the air inlet and no radiators at the inner face - solution: atrium temperature at 20 C; - visual comfort problems by reflection of light bulbs in the standard glass walls;- water problems due to leaky water wall pool ADDITIONAL BENEFITS (PR, GREEN LABELS ETC. ) - Hugo-Häring-Preis 1997 BDA Bund Deutscher Architekten, Landesverband Baden-Württemberg, - WWF-example building - PR-effect: in Europe the client company is now well known through architectural publications - internal used for company PR