According to the Czech legislative act the operative temperature is the evaluation criterion for thermal comfort in air-conditioned or heated spaces. The operative temperature respects the air temperature; mean radiant temperature and air velocity. For mean radiant temperature calculation the surface temperature of the surrounding walls must be known. Manual calculation of the mean radiant temperature is very complicated and not suitable for practical usage since the surface temperatures are difficult to determine. On the contrary, the computer-based calculation is prepared to do this automatically and could be particularly useful when seeking multiple solutions for a problem under the optional conditions. The paper presents the operative temperature analysis in a space, using the dynamic simulation method, respecting the inside and outside climatic changing effect. Three typical rooms were chosen for the analysis: a single façade room, a corner room and a room under the roof. The rooms were analysed in a light of external wall mass, glazing ratio and quality. Three façade types were used in the model. The simulations were examined for extreme and reference summer weather conditions in the Czech Republic.