There is still an obvious and indisputable need for an increase in the efficiency of energy utilisation in buildings. Heating, cooling and lighting appliances in buildings account for more than one third of the world?s primary energy demand and there are great savings potentials. This book provides methods and models for heat and mass transfer processes in buildings, which have a vital impact on the energy utilisation. These models can be used in optimisation procedures aiming at increasing efficiency in the energy use, i.e. at minimising consumption of high quality energy, exergy, in buildings. The thermally activated building components are examples of these systems which can help to reduce exergy consumption caused by heating and cooling of rooms. The developed macro element modelling approach is generally suitable for modelling the dynamic behaviour of such combined systems with a heat carrier flow and solid construction parts with substantial heat storage capacity. The presented work will help professionals from engineering and research within the building field to increase the understanding of where and how to find new energy efficiency potentials.