One of the first passive energy standard office buildings in Europe was extensively monitored over 3 years to analyse the summer performance of highly insulated, well sun-shaded and mechanically ventilated buildings. During typical German summer conditions with less than 160 hours ambient air temperatures above 25 degrees C, these buildings perform excellently during summer, even if the internal loads are rather high with 200-400 Wh m(-2) day(-1). If ambient air temperatures are significantly higher like in summer 2003 with more than 3 K higher average temperatures than usual, nearly 10% of all office hours are above 26 degrees C. Detailed measurements showed that the night discharging of heavy thermal masses such as the concrete ceiling was not always effective under free convection conditions. Room air temperature decreased by 2-3 K only although measured night air changes were always above 5 h(-1). The measured air change rates contained not only cool ambient air but also backflow of warmer air from the corridors, which could be shown by flow visualisation in the rooms and by simulation studies. Improvements to the night ventilation performance can be achieved, if early evening ventilation with high heat gains can be reduced and if fans support the air exchange in the cooler morning hours. Three year measurements and simulation of the earth heat exchanger showed that excellent performance is achieved with COP's between 35 and 50. Due to the limited fresh air volume flow in such buildings, the earth heat exchanger only removes a fraction of the loads, here about 18% of the total internal loads. (C) 2005 Elsevier B.V. All rights reserved.