Lean buildings: Energy efficient commercial buildings in Germany

The paper presents the description and initial evaluation of a number of commercial large scale buildings (>1000m2) situated across Germany. The study has been carried out within the framework of the evaluation 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 at the design stage of the buildings for additional investigations and simulations of variants, which feature elements of passive cooling, and after construction for a thorough monitoring of the finished buildings. The absence of investment subsidies ensured that all design solutions were realized under representative economic conditions. The technical requirements for admittance of a building to the program were an anticipated total primary energy use (heating, cooling and lighting) below 100 kWh/(m2a) [31,700 Btu/(ft2a)] combined with excellent vis ual and thermal comfort conditions. These ambitious goals can only be reached by a lean building featuring increased thermal insulation, intensive use of daylight and a strategy for passive cooling. The reduced HVAC-system relies heavily on a building whose design carefully considers the given climatic boundary conditions. In the moderate German climate, the focus usually lies on the avoidance of unwanted solar gains in the summer. The remaining internal loads can often be counterbalanced by controlled ventilation, additional nocturnal ventilation or by earth-to-air heat exchangers