TOWARDS LEAN BUILDINGS - EXAMPLES AND EXPERIENCE FROM A GERMAN DEMONSTRATION PROGRAM FOR ENERGY EFFICIENCY AND SOLAR ENERGY USE IN COMMERCIAL BUILDINGS Karsten Voss, Christoph Reinhart Solar Building Design Group, Fraunhofer Institute for Solar Energy Systems Oltmannsstrasse 5, 79100 Freiburg, Germany, Tel: #49/761/4588-135, Fax: -132, email: karsten.voss@ise.fhg.de Günter Löhnert sol ° id ° ar, Forststrasse 30, 12163 Berlin, Germany Tel: #49/30/8270-4191, Fax: -4192, email: solidar@t-online.de Andreas Wagner Faculty of Architecture, University of Karlsruhe, Englerstrasse 7, 76128 Karlsruhe, Germany Tel: #49/721/608-2178, Fax: -6090, email: wagner@lbta.arch.uni-karlsruhe.de Abstract – The paper presents the description and initial evaluation of a number of commercial large scale buildings situated across Germany. The study has been carried out within the framework of the demonstration program SolarBau, which has been initiated and funded by the German Ministry of Economy and Technology. The program funds up to 25 demonstration buildings and their collective evaluation. Funding is only provided for the design of the buildings – for increased energy-related planning and simulations - and for thorough monitoring after construction. The absence of investment subsidies ensured that all design solutions were realized under representative economic boundary conditions. The technical requirement for admittance of a building to the program is an anticipated total annual primary energy use (heating, cooling and lighting) below 100 kWh per m² net floor. These ambitious goals can be reached advantageously by a so-called lean building featuring increased thermal insulation, intensive use of daylight and a strategy for passive summer cooling. The reduced HVAC system relies heavily on a building with appropriate design for the given climatic boundary conditions. In the moderate German climate, the focus for commercial buildings lies on the avoidance of unwanted solar gains in the summer. The internal loads can mostly be counterbalanced by increased utilization of the thermal inertia of the building combined with nocturnal ventilation or supplementary earth-to-air heat exchangers for pre-cooling of the building`s supply air. 1. INTRODUCTION Energy needs of offices are different to those of residential buildings (Esbensen Consulting Engineers, 1998). They consume more electricity per occupied floor area due to intensive use of HVAC systems and office equipment, Fig. 1. Several circumstances have supported a trend to an increasing electricity demand (Nilson, Uppström, Hjalmarsson, 1997): 1. Many modern office buildings aim to create a time and site independent indoor climate, which approaches a narrow, trans -global specification for what are considered to be adequate working conditions (Baker 1999). As the tolerance range of the users diminishes, the need for powerful HVAC equipment rises together with the energy demand. The effect is reinforced if work places are grouped together in large offices. 2. Commercial buildings often function to communicate a company`s corporate identity. This has lead to building styles which ignore the climatic boundary conditions for the sake of a desired visual impression. 3. As modern office buildings exhibit rising internal load profiles due to the explosive increase in the use of electrically powered office equipment like PCs, printers and other technical equipment, the cooling loads start to dominate the overall energy demand even in moderate climates. The peak of this development seems to have been reached as more energy-efficient appliances are finding their way into offices, e.g. LCD computer displays and fluorescent lamps. In Switzerland, the main motivation for purchasing these new appliances has been found to be often unrelated to the better energy performance of the devices (Weber and Keller 1999). It is merely a positive side effect that new articles tend to have a lower energy demand. The tendency towards electrically driven, cooling-dominated HVAC systems worsens the overall CO 2 balance of a building. Growing use of artificial lighting to provide glare-free lighting conditions for PC work further foster this development. 4. Energy-saving measures and building energy codes tend to concentrate on the thermal envelope since the heating energy demand used to dominate the total energy demand of a building in the past. An exception to this is the Swiss SIA 1 building code which formulates energy bench numbers for heating as well as electricity for HVAC and lighting electrical energy use. Fig. 2 shows 1 SIA: Swiss Society of Engineers and Architects