Hans Erhorn (Erh) is head of department heat technology at the Fraunhofer Institute of Building Physics. He holds a degree in environmental engineering from Hermann Rietschel Institute of Berlin University of Technology. Erh is a specialist in developing energy concepts for buildings and estates, energy efficient building components and ventilation strategies as well as simulation tools. He has been project co-ordinator of about 150 national and international research, development and demonstration projects within the last 20 years. He was the coordinator of the EU 6th FP project BRITA in PuBs which has ended in 2008. Current involvement in European projects include Concerted Action EPBD (Core theme leader), the BUILD UP platform, IEE ASIEPI and IEE CENSE. Erh acts as Subtaskleader in 4 research projects on low energy houses, daylighting and simulation tool within the IEA Energy Conservation (ECBCS) and Solar (SHAC) Programs and was the Operating Agent in the retrofit project of educational buildings in the IEA – ECBCS program (Annex 36). He was national scientific coordinator in the longterm German national retrofit research program (EnSan) and is chair of the coordinating panel for standardization on energy efficiency in Buildings in Germany and coordinator and member in different ISO, CEN and DIN standardization committees. Erh also acts since 1990 as assistant professor at Stuttgart University and was visiting professor 2002 at Graz University of Technology.