Design tool used to explore the complex dynamic behaviour of buildings for different designs. The behaviour is expressed in terms of temperatures, heating- and cooling loads and different comfort indices. The form of the building can be modelled in a flexible way. The model for assessing the solar insolation on building surfaces is detailed and includes the influence of different types of shading devices. The window model has been improved and calculates properties for a window package in an accurate way. The simulation uses a time step of one hour and calculates values in response to hourly values for climatic data, internal loads and airflows.