Active heat capacity : models and parameters for the thermal performance of buildings

Sammanfattning: The thesis concerns the characterization and evaluation of nonsteady heat transfer in building components and building enclosures. The major aim of the underlaying research has been to assemble and develop simplified calculation procedures for this purpose. To establish a simple model for heat balance calculations three main items are treated: simplification of the heat transfer operators, the description of the solar gain through windows and reduction of the number of transfer paths. For nonsteady heat conduction in opaque construction solutions are given in the frequency domain and by finite differences. Based on the frequency response different types of RC-models are derived. The simplest network is a single capacitance giving the same ratio between the amplitudes of heat flow and temperature as the real surface. This quantity is called the active heat capacity of the wall. To estimate this quantity a simplified calculation procedure is given. For the combination of surfaces with different active heat capacities addition rules are established that take into account the limited mutual radiation exchange between the surfaces. In that way the room is transformed into a model with two nodes, one representing the surface temperature and one representing the room air. A solution in the time domain allows the thermal loads to be represented as time series and the mode of operation can be freely defined and varied during the calculated period.