The paper presents the results of the analysis of energy consumption and actual cooling and heating demand in the museum rooms located in two different buildings: the old one, historic building and the modern building constructed as a museum. The simulations were carried out by the ESP-r software for the models of the rooms which were assumed to be used as auditorium with the possible presence of many people which results in large internal heat gains. The calculations provide the possibility to compare the energy demand both in winter and summer months for heating and cooling purposes for different schedules of the internal heat gains from people. The results prove that the ability of the partitions to accumulate heat permits to reduce the effects of the increasing internal loads and is quite important for the thermal and humidity balance of the room especially in case of large gains from the people gathered in the rooms.