Flowfields around bluff bodies are characterized by complex distributions of the strain-rate tensor. Such flowfields can be analyzed with various turbulence models. The shortcoming of the eddy viscosity modelling in the k-e model is scrutinized in comparison with the results of ASM. The accuracy of the algebraic approximation adopted in ASM is examined using the numerical data given from LES. A new LES model with variable Smagorinsky constant is then presented.
The paper considers issues pertaining to the capabilities and limitations of computational methods for multidimensional turbulent flows of the type encountered in fluids engineering. It argues that CFD, whilst offering considerable predictive power and potential, is not yet sufficiently well established to be applied routinely to complex 3D flows, unless only a rough qualitative. statement is being sought.
Since the cost of energy is increasing sharply a trend to conserve energy in the indoor environment and in addition to improvements in thermal insulation, two possible solutions are adopted. The first one is to provide reduced air gaps and opening for newly constructed buildings to minimise the infiltration of outdoor air. The second one is to reduce the ventilation rate or the fresh air supplied in air conditioned buildings. These two solutions are the reason for some serious problems of indoor air quality.
In order to evaluate the accuracy of COMIS predictions for large openings,and to study its sensitivity, two tests have been performed. In the first test, COMIS is used together with four existing multizone air flow models to calculate natural ventilation in a building for various climatic and opening configurations. In the second test, COMIS predictions are compared with single-sided ventilation measurements taken in test cells. The results of the tests are reported.
The objectives of this project were to develop and test a simplified duct-leakage measurement technique that could be used as part of both new-construction and retrofit DSM programs for residential duct systems.
As part of a project financed by the National Foundation for Energy Research (NEFF), the Building Services Section at the EMPA examined the thermal behaviour of one building, with zero energy demands, located in a low energy housing estate in Waedenswil on the border of the lake of Zuerich. The estate was initiated by Dr. R. Kriesi who also made the energy concept. The architect was R. Fraefel and the estate was financed also by the government of Zuerich. The measures taken in order to reach a minimal heating demand in the chosen zero energy test house were as following:
A basic condition for low energy houses is a demand controlled ventilation combined with an air-tight building envelope. Within the scope of different research projects financed by public grants and measurements effected by private order mainly in the south of Germany, the airtightness in low energy and minimum energy houses has been checked according to the DC pressurization method and the places of leakage have been determined. Considering the results with respect to the recommendations of the SIA 180 (standard of Switzerland), 40% of approx.
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