Interaction of building envelope and cooling ceilings - system analysis and system modeling

Abstract

The aim of the work is, to provide an easy to handle planning support tool that takes into account the different influencing parameters regarding the resulting room conditions and therefore the comfort in the room. The prediction of thermal comfort in buildings plays a key role in constructing energy efficient buildings and at the moment it cannot be fully implemented. In the completeness complex flow processes in different façade systems, the dynamic of building elements' performance in combination with the control system is a great, so far, unresolved challenge. For the development of a simplified calculation model a series of measurements have been done in an existing office building with different façade systems. The measurement results show that there is an impact on the cooling capacity of a cooling ceiling and the operative temperature and therefore also on the comfort by different façade systems. Furthermore the measurements are used for the validation of the mathematical model. For the thermal calculation a room model based on the program Matlab/Simulink was built. A CFD Model (with the program Comsol) realizes the mapping of the air flow. The boundary conditions for the CFD Model are the results of the thermal calculation. The goal is to define a sufficiently accurate picture of the flow characteristics in rooms. The results of the CFD calculations allow a simplified integration into the thermal model using distribution factors and mass balances. The validation of the calculation results with the measurement results shows that a fully coupled simulation (coupling of thermal and air flow calculation) is not required for the prediction of room conditions and the thermal comfort in rooms. Neglecting the flow characteristics in rooms can lead to incorrect results, especially for complex façade systems in combination with component activation (e.g. cooling ceiling). Based on the validated model, recommendations for future office and class room designs in net energy producing buildings can be formulated. To accomplish this, simulations over typical day to day cycles as well as yearly cycles can be conducted.