Fakultät für Angewandte Natur- und Geisteswissenschaften
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- Fakultät für Angewandte Natur- und Geisteswissenschaften (4) (entfernen)
Building Energy Simulation (BES) tools play a key role in the optimization of the building system during the different phases, from pre-design through commissioning to operation. BES tools are increasingly used in research as well as in companies. New BES tools and updated versions are continuously being released. Each tool follows an independent validation process but rarely all the tools are compared against each other using a common case study. In this work, the modelling approaches of widespread dynamic simulation tools (i.e. EnergyPlus, TRNSYS, Simulink libraries CarnotUIBK and ALMABuild, IDA ICE, Modelica/Dymola and DALEC), as well as PHPP (a well-known quasi-steady-state tool), are described and the results of all the tools modelling the same characteristic office cell, defined within the IEA SHC Task 56, are compared on a monthly and hourly basis for the climates of Stockholm, Stuttgart and Rome. Unfortunately, different tools require different levels of input detail, which are often not matching with available data, hence the parametrization process highly influences the quality of the simulation results. In the current study to evaluate the deviation between the tools, frequently used statistical indices and normalization methods are analysed and the problems related to their application, in a cross-comparison of different tools, are investigated. In this regard, the deviation thresholds indicated by ASHRAE Guideline 14-2014 are used as a basis to identify results that suggest an acceptable level of disagreement between the predictions of a particular model and the outcomes of all models. The process of reaching a good agreement between all tools required several iterations and great effort on behalf of the modellers. To aid the definition of building component descriptions and future references for inter-model comparison a short history of the executed steps is presented in this work. Together with the comparison of the results of the tools, their computational cost is evaluated and an overview of the modelling approaches supported by the different tools for this case study is provided aiming to support the users in choosing a fit-for-purpose simulation tool.
Correlations between standardised and real impact sound sources in lightweight wooden structures
(2021)
This study aimed to understand the correlation between standard impact sound sources and real impact sources in lightweight floor structures. Six real impact sources (adult walking, child running, child jumping on the floor, and three objects falling) were used to be compared with standard impact sources (i.e. tapping machine and impact ball). Measurements were conducted on a lightweight timber joist floor. Impact sound pressure levels (SPLs) produced by the standard impact sources were measured on the four floor structures with or without carpet tiles. For the real impact sources, two walkers wearing socks and slippers walked at different speeds (normal and fast) along three paths, while two children ran along the three paths and jumped at four positions. Also, the SPLs generated by dropped objects were measured at five positions. Seven standardised single-number quantities (SNQs) were calculated for the tapping machine and the impact ball, while three noise ratings (LAeq, LAFmax, and LN) were also computed from the sound recordings of the real impact sources. Both the tapping machine and the impact ball showed similar frequency characteristics with the real impact sources across all the floor structures. All the SNQs for the tapping machine and the impact ball were highly correlated with the energy-based noise ratings of the adult walking and little differences were found across walking speeds and footwear. Similar tendencies were observed from other real impact sources, indicating the high correlations between the standardised SNQs of the tapping machine and the impact ball and the noise ratings.
We report on an investigation of student thinking about steady-state pipe flow of an incompressible fluid. About 250 undergraduate engineering students were given a test consisting of two hydrodynamics questions, combining multiple-choice format with subsequent open-ended explanations. There is substantial evidence that students have difficulty applying and prioritizing the two basic principles of mass conservation (expressed in the continuity equation) and energy conservation (i.e., Bernoulli’s equation). When faced with questions that involve gravity, dissipative effects (“friction”), or a visible pressure drop, a considerable number of students did not invoke the continuity equation in situations where applying it is a necessary step for arriving at the correct answer. Instead, even after lecture instruction on this topic, many of the first-year students based their answers on ill-supported assumptions about local pressures. Some of them used formal arguments from a simplified Bernoulli equation (“lower pressure means higher velocity”), while others based their answer on intuitive arguments (“higher pressure leads to higher velocity”). We also found reasoning based on analogies to single-particle motion (“flow velocity decreases when flowing upwards or friction is present”). Contrary to other researchers, we did not see any evidence for the hypothesis that students think of water as a compressible fluid. Instead, students’ answers often indicate a lack of understanding of the conservation of mass or its implications for incompressible fluids or of the role that this principle plays in the context of fluid flow. In addition, our data indicate that some students have more general difficulties in describing and reasoning about technical situations, such as applying equations containing multiple variables, distinguishing spatial differences in a quantity from its changes with respect to time, or realizing the meaning of idealizations. We also present some evidence that different levels of activation of students during instruction influence the prevalence of these difficulties and discuss some implications for instruction.