In moderate climates, one promising approach to reduce the energy demand of office buildings for air conditioning without reducing comfort is passive cooling by night ventilation. The office building of DB Netz AG in Hamm (Germany) has been designed, constructed and monitored for a long period in the framework of the German research programme, "Solar Optimised Buildings", SolarBau for short. Monitored data of room and ceiling temperatures in 12 office rooms, supply air flow rate and temperature in these office rooms, electricity consumption for each office room, climate and air temperatures in an adjacent atrium are evaluated by a new method for analysis which deals with short-term and long-term measurements and building simulation. The monitored data from the office building, which is used as such, are complemented by information from the building management system about the position of louvers and the shading devices. The contribution of simulation tools to the design of buildings with passive cooling by night ventilation is evaluated by a comparison between monitored data and simulation for a long period. (C) 2004 Elsevier B.V. All rights reserved.