The complete refurbishment of nine buildings, each containing ten apartments of $72;m^2$ is presented, and preliminary results are shown. The buildings have a different retrofit scenario in terms of insulation, heat production and delivery, domestic hot water production and air-handling systems. Following the energy saving ordinance for buildings in Germany of the year 2007 [1] each building has been evaluated. A monthly energy balance based on weather data from the German test reference year has been calculated for a one year period. The results show that depending on the refurbishment solution, the retrofit can reduce the energy demand up to 93%, and increases thermal comfort. Within the next three years, the buildings will be monitored in high time resolution. Physical models of the buildings and the components are under development using the modeling language Modelica, and will be validated through measured data. Once validated, the models will be used, for example, to elaborate regulation strategies for the plants and to create new virtual refurbishment versions in the direction of a zero-impact building.