One salient finding in the three buildings at Blaue Heimat, Rislerstrasse KfW60 and KfW40 was the relative high hot water consumption at 28 kWh/(m2NFAa) (including circulation). This value is 70 % above the target. In addition, Blaue Heimat had 6 kWh/(m2NFAa) of distribution and storage losses due to the central system used. Energy consumption for hot water was much lower in Freyastrasse at

18.4 kWh/(m2NFAa), which was below the target value; part of the reason was the lower number of occupants and the lower circulation losses.

3.1 Energy supply

The cogeneration unit in the Blaue Heimat building provides almost all of the heat required. On the average, the cogeneration unit had an efficiency of 89 % and covered 96 % of the heat demand. Thus the possibility of a high CHP fraction as an important part of a net zero energy strategy is shown. Even though the pipes were well insulated (200% compared to the German standard) the storage and distribution losses become a non neglecting part of the delivered heat. The chopping of the CHP unit was suppressed applying an appropriate sizing of the storage.

In Rislerstrasse, the gas-condensing boiler and storage tank had an average efficiency of 85 % in 05/06 and 91 % in 06/07, which were as expected. The solar collectors covered 40 % of hot water demand in Rislerstrasse, which is a quarter of the overall heat demand.