Thanks everybody.
Shame on me! The infiltration in model A was assigned to a zone list (containing all building zones), while I had the HVAC system only in one zone. So problem solved and I am happy as I learned a lot of stuff because of this funny mistake!
Best,
Farhang
Univ. Ass. M.Sc. Farhang Tahmasebi
Department of Building Physics and Building Ecology
Vienna University of Technology