The heat source for the system is outside air. For DHW a second heat pump using exhaust air as heat source is installed. The heating circuit contains a buffer storage. The system uses a separate heat pump for DHW where a DHW storage is integrated additionally. The usage of exhaust air as heat source for DHW creates good preconditions for the heat pump's efficiency as the exhaust air 's temperature is usually higher than the outside air. In addition, underfloor heating further contributes to good efficiency values as this distribution system can be operated with relatively low inlet tempertures.   

In 2010, efficiency amounted to 3.4 and was significantly higher compared to the average of 2.9. The good value results from low inlet temperatures in the heating circuit and the exhaust air's temperature for the second heat pump. Both back-up heaters have a share of 1 % of the total electrical energy demand which is below the average of 4 % and as a consequence positively influences efficiency. The share of DHW in 2010 amounted to 6 % and thus was far below the average of 19 % which also had a positive effect on efficiency.