One of the first rehabilitated passive energy standard office buildings in Europe was extensively monitored over two years to analyse the cooling performance of a ground heat exchanger and mechanical night ventilation together with the summer comfort in the building. To increase the storage mass in the light weight top floor, phase change materials (PCM) were used in the ceiling and wall construction. The earth heat exchanger installed at a low depth of 1.2 m has an excellent electrical cooling coefficient of performance of 18, but with an average cooling power of about 1.5 kW does not contribute significantly to cooling load removal. Mechanical night ventilation with 2 air changes also delivered cold at a good coefficient of performance of 6 with 14 kW maximum power. However, the night air exchange was too low to completely discharge the ceilings, so that the PCM material was not effective in a warm period of several days. In the ground floor offices the heat removal through the floor to ground of 2-3W m(-2) K(-1) was in the same order of magnitude than the charging heat flux of the ceilings. The number of hours above 26 degrees C was about 10% of all office hours. The energy performance of the building is excellent with a total primary energy consumption for heating and electricity of 107-115 kW h m(-2) a(-1), without computing equipment only 40-45 kW h m(-2) a(-1). (C) 2009 Elsevier Ltd. All rights reserved.