The objective for the thesis is to investigate how to model many people when using a CFD code to simulate airflows in large enclosures with high density of people as for instance cinemas, concert halls, lecture halls etc. From a litterature study there was found no distinct sign of thermal reciprocal action between people subject to the density of people which can be expected in cinemas, concert halls, lecture halls etc. By using four different densities of people the thermal reciprocal action was investigated experimentally in an auditorium. From the experiment there was not found any indication of thermal reciprocal action between the people or that the investigated density of people would have influence on their thermal state of mind. In the litterature study it was also found that people are assumed to act as individuals when simulating airflow in large enclosures with many people and thereby taking no account to thermal reciprocal action between the people. Therefore it was concluded in the project that when modelling many people they can be assumed to act as individuals and not include any thermal reciprocal effetcs. Different proposals to model many people in a large enclosure were examined with the use of numerical models in the CFD code ANSYS-CFX. Main findings from the simulations was that the temperature fields indicate that the temperature gradient is not constant in the height of the room and a high level of mixing in the air above the occupied zone occurs. Moreover it was found that the highest velocities occurs above the persons and increases in the height of the room.