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Phase Change Materials (PCMs) can enhance thermal mass and energy efficiency in lightweight buildings. In this work, the thermal behaviour of plasterboards with incorporated microencapsulated PCM is investigated. These PCM wallboards are mounted in office rooms of the Energy Efficiency Center (EEC) in Würzburg (Germany). The experimental results show that the PCM wallboards can provide a passive cooling power of up to 8.4 W/m2. However, the regeneration behaviour of PCM during the night critically influences their thermal performance for the next day. In the period from April to September of the years 2015 and 2016, the average regenerated (solid) fraction of the PCM in the wallboards at the beginning of each day was only 20 %, even though the regeneration is supported by the nightly operation of cooling ceilings. In order to improve the thermal performance of the wallboards this problem has to be addressed. Therefore, a case study is performed with the thermal building simulation software TRNSYS 17. In this simulation, a night ventilation is used to enhance PCM regeneration, whereas active cooling by means of the cooling ceiling only takes place during the day. The simulations were carried out for two PCMs differing in the melting range. The simulation results reveal that the regeneration of the PCM wallboards could be increased by a factor of 2, which directly increases the latent heat storage capacity in rooms and reduces the temperature rise during daytimes. Compared to a reference room without PCM wallboards, the electrical energy demand for active room cooling is reduced by 30 %.