The microclimate in the libraries should provide conditions both for the stored collections (books, paintings, etc.), not to lead to their destruction, not to cause discomfort to the working people and not to act destructively on the exploitation of this type of rooms. The analysis of thermal comfort parameters was performed for the three rooms of the Main Library of Lodz University of Technology by building geometric model and using the DesignBuilder software. Boundary conditions were determined experimentally, by the measurements carried out in the library rooms, by measuring air velocity and temperature within. The received from the numerical analysis distributions of temperature and air velocity in the zones of human presence were compared with the guidelines presented in Polish standards.