1.1. LE-OLD

There is no official definition of specific goals and figures for low energy buildings. Some attempts have been made to define a low-energy building. In general, it refers to a building built according to special design criteria aimed at minimizing the building’s operating energy [11].

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Figure 1 gives an overview of the estimated energy consumption of the building stock and the energy target for aggregate net energy demand for different building types in kWh/(m2 a) [5,12]. It shows that the new building regulation requires a drastic reduction in energy consumption (i. e. 50% in commercial buildings and 31% in office buildings). In Germany, the ‘lean building’ has been defined with specific primary energy consumption of 100 kWh/(m2a) [14]. The new energy labelling system will help to categorize the levels of energy use in buildings [15].