The paper presents the results and analysis of the energy consumption of a newly designed office building in relation to quality of the indoor environment. The main energy consuming process in such a type of buildings is air-conditioning and cooling. The building was designed as a low-energy one, cooled by means of cooling ceilings. The architects and designers assumptions were checked by numerical simulation applying ESP-r software. Basing on the simulation results, the seasonal energy consumption was analyzed for different strategies of cooling. The changeability of the demand for cooling was also simulated for the summer period for one of the Polish towns. Thermal comfort in the building was assessed thanks to the simulation of the variability of the indoor air temperature, the temperature of the partitions and by means of the PMV factor.