Heating

Five of the buildings shown in figure 2 show a heating energy consumption (end en­ergy) of less than 40 kWh m-2a-1 which is mostly due to the high insulation standard. The mean U-values of these buildings are between 0.21 and 0.43 W m-2K-1. Four of all funded buildings (3 offices, 1 factory) reach the passive house standard with a maximum heat load of 10 W/m2 and air heating systems. In buildings with a high in­sulation standard and a heat recovery system, almost the complete heating energy is required below ambient temperatures of 13 °C. The mean room temperatures in the offices lie around 22 °C which corresponds to experiences from domestic dwellings. Passive solar gains play a minor role in most of the buildings because combined ex­terior glare and sun protection systems are used frequently. Also the favouring of south-orientated glazed facades for office rooms often leads to a functionally and economically unfavourable design solution for the whole building.

Ventilation

Since ventilation losses become dominant in large compact buildings, most of the funded buildings have a heat recovery system. Air change rates in the winter are around 1 h-1. Due to different systems the efficiencies (ratio between heat supply and electric energy demand) vary between 5.7 kWhth/kWhei (LAMPARTER, flat plate heat exchanger with a heat recovery efficiency of 80%) and 3.3 kWhth/kWhel (POLL — MEIER, exhaust air system with heat pump). Air leakage rates are very low for almost all buildings (n50 << 1.2 h-1). In a lot of buildings atria are included into the ventilation concept, serving either for collecting exhaust air (figure 3) or distributing fresh air.

Figure 3: Ventilation concept of the KfW building in Frankfurt