Since the Energy Performance of Buildings Directive (EPBD) was accepted and implemented over the course of the last years, buildings are audited energetically to receive the necessary construction licenses. This augmented the already high attention for research on innovative (passive) energy-saving concepts even further. Validation of the viability – energetical, economical, ecological, comfortwise … - of these innovative systems thus became an important issue. The performance of mechanically driven night ventilation, combined with an earth-air heat exchanger (EAHX) and a heat wheel, as an active cooling replacement in a high profile office building in Nazareth (Belgium) is assessed through measurements and simulations of the concept. First results indicate that both the EAHX and the heat wheel deliver substantial energy savings, whereas the mechanically driven night ventilation seems incapable of doing the same. The measured supplementary electric fan energy at night is within the range of the avoided cooling energy predicted by simulations. By means of more detailed modelling of variants, this problematic balance is investigated further in order to optimize the system design and control. This will create a better understanding of the value of the concept.