Master's Thesis Lukas Wintgens

 

Development and validation of a CFD model for room air flow analysis in the Aachen Comfort Cube (ACCu)

Master's Thesis Wintgens Copyright: EBC

In the development of indoor air conditioning systems the thermal comfort has increasing importance. For thermal comfort assessment and improvement a 33-node-comfort-model (33NCM) is planned to be calibrated and validated for displacement ventilation systems at the Institute for Energy Efficient Buildings and Indoor Climate (EBC) at the RWTH Aachen University. The model is based on the data of a test series conducted with test persons. For further validations it is necessary to recreate the local heat transfer at different body parts, therefore the 33NCM is linked with a Computational-Fluid-Dynamic model of the Aachen Comfort Cube (ACCu) test bench. The implementation of this model is the main subject for the present work. For that a test series with thermal manikins is used to create an environment of repeatable boundary conditions inside the ACCu. Main aspects of the tests are the analysis of the overall flow domain, as well as the temperature distribution around the thermal manikins at different thermal gradients and different mean temperatures. The CFD-simulation is superior to real tests in terms of time and spatial resolution. For future investigations, the CFD-model will be coupled to the 33NCM to identify and evaluate potential for improvement of thermal comfort prior to an expensive test series.

At first the principle of displacement ventilation is introduced which is superior to the mixed ventilation in terms of energy efficiency. The mathematical basics of numerical fluid calculation are explained. The primary aspect is the modeling of turbulence flow and the valid recreation of the heat transfer. The modeling of the slow buoyancy-driven flow is also important. The ACCu is reconstructed using a Computer-Aided-Design software. In the next step, the results of the test series are analyzed and used as boundary conditions for CFD-model. The spatial discretization of the flow domain is realized using a three-dimensional mesh. The turbulence model and the radiation model are chosen considering the buoyancy-driven flow. Model settings and assumptions are validated using the results in addition to taking the necessary computing time into account. Main criteria here are the different temperature gradients and the velocity distribution measured in the test series. The primary goal is to minimize the difference between the simulation data and the test data. The results are analyzed and compared to the test series. Finally, the quality of the model is evaluated concerning its use in the determination of thermal comfort and the coupling to the 33NCM. In the outlook possible improvements to the model and reasonable additional investigations are presented.