@article{ParzingerHanfstaenglSiggetal.2022, author = {Parzinger, Michael and Hanfstaengl, Lucia and Sigg, Ferdinand and Spindler, Uli and Wellisch, Ulrich and Wirnsberger, Markus}, title = {Comparison of different training data sets from simulation and experimental measurement with artificial users for occupancy detection — Using machine learning methods Random Forest and LASSO}, series = {Building and Environment}, volume = {223}, journal = {Building and Environment}, doi = {10.1016/j.buildenv.2022.109313}, pages = {109313}, year = {2022}, abstract = {The applications for occupancy detection range from controlling building automation and systems, determining heat transfer coefficients and even assessing the risk of infection in rooms. Studies in the literature use various statistical models, physical models and machine learning techniques to detect occupancy. All these methods require data for training the occupancy detection models. However, data generation is time-consuming and expensive. This study demonstrates the feasibility of using simulated learning data. Using three different data sources, we tested the suitability of different methods for generating learning data. We conducted two experiments in two office spaces with a real user and an artificial user, and we generated a third data set using a building simulation model. In addition, this study compares two different machine learning approaches (Random Forest and LASSO) using environmental parameters. Both machine learning approaches could develop models with a sensitivity of at least 83 \% and a specificity of at least 97 \% with both training data sets. This work shows that it is possible to determine the presence in rooms using simulated data. The results compared to measured data were just slightly less accurate, and the added value due to the lower effort was considerable}, language = {en} } @inproceedings{Kellner2022, author = {Kellner, Robert}, title = {Making Effective Videos For (Live) Online Learning Quickly}, series = {Proceedings of the IUPAP International Conference on Physics Education}, booktitle = {Proceedings of the IUPAP International Conference on Physics Education}, address = {Sydney}, isbn = {978-1-74210-532-1}, pages = {109 -- 109}, year = {2022}, abstract = {Abstract for the presentation held at the 2020 International Conference on Physics Edcucation}, language = {en} } @inproceedings{SchelerDaumeSojitraetal.2022, author = {Scheler, M. and Daume, D. and Sojitra, D. and Neumeyer, T. and Steinbach, S. and Beck, T. and Schulze, A. and H{\"u}ttl, B.}, title = {Precise On-Site Power Analysis of Photovoltaic Arrays by Self-Reference Algorithm}, series = {Proceedings of the 8th World Conference on Photovoltaic Energy Conversion}, booktitle = {Proceedings of the 8th World Conference on Photovoltaic Energy Conversion}, pages = {4}, year = {2022}, abstract = {To detect degradation of photovoltaic systems at an early stage, precise performance determinations are essential. Current-voltage measurements on single modules in indoor labs under well-defined conditions are state-of-the-art. However, this method causes a logistical and economic effort. On-site measurements reduce the effort but are prone to error because of poorly determinable test conditions: The detected temperature on the backside of modules as well as the irradiance detected by pyranometer in tilted module plane usually differs from the actual operating conditions. In consequence, the accuracy of measured current-voltage characteristics is poor. A precise on-site power determination is achieved by a self-reference algorithm. Improvements by self-referencing are not achieved by correcting the raw electrical data, but by replacing the measured test conditions (temperature and irradiance) with effective data. These effective values correspond better to the actual module irradiance and temperature values. Furthermore, precise power determination of photovoltaic arrays requires to identify and exclude emporarily deformed current-voltage curves from consideration, as it can arise from non-uniform irradiation within array like shading. In this paper, the application of a digital curve filter is reported and performance determinations by a self-reference algorithm are demonstrated on a photovoltaic array. We review and discuss the measurement concept in terms of its ease of use. … }, language = {en} } @unpublished{KimmerleDvorskyLiessetal.2022, author = {Kimmerle, Sven-Joachim and Dvorsky, Karl and Liess, Hans-Dieter and Avenhaus, Rudolf}, title = {Time to Failure under Varying Thermal Stresses}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:861-opus4-19126}, pages = {30}, year = {2022}, abstract = {Varying thermal stresses influence significantly the time to failure of electric components as used, for instance, in automotive devices. For applications as autonomous driving a high reliability has to be guaranteed. In this article we discuss how to combine probability distributions for failure. Discrete and continuous changes of the probability distribution in time are both considered. It turns out that the temporal order of the distributions, corresponding to the succession of stresses in applications, is essential. The latter observation restricts the general applicability of the widely used temperature collectives where only the total time of a temperature stress is considered neglecting the order of the stresses. An application of our results are thermal overstress tests on electric components. We may explain yet not well understood measurements for automotive electric cables.}, language = {en} } @inproceedings{SchaefleGraupnerStanzel2022, author = {Schaefle, Claudia and Graupner, Franziska and Stanzel, Silke}, title = {TOWARDS A THERMAL CONCEPTUAL ASSESSMENT FOR FIRST-YEAR ENGINEERING STUDENTS - TCA-1Y}, series = {Proceedings of the 11th international conference on Physics Teaching in Engineering Education}, booktitle = {Proceedings of the 11th international conference on Physics Teaching in Engineering Education}, organization = {SEFI - Soci{\´e}t{\´e} Europ{\´e}enne pour la Formation des Ing{\´e}nieurs}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:861-opus4-18637}, pages = {6}, year = {2022}, abstract = {We report from an ongoing process to develop a thermal conceptual assessment that covers the essential concepts of first-year thermodynamics to be administered to engineering students. The goal is to develop a measurement instrument in order to investigate students' pre-knowledge as well as the influence of teaching and learning settings. The assessment builds on known misconceptions and concept questions described in the literature. The original items have been modified significantly in the current version 3 of the test in order to create single-choice questions with four distracters each that address frequent misconceptions from student answers in a systematic way. The working process to create these distracters is described exemplarily.}, language = {en} } @inproceedings{DaumeSchulzeSchneideretal.2021, author = {Daume, D. and Schulze, A. and Schneider, S. and Neumeyer, T. and Beck, T. and Steinbach, S. and H{\"u}ttl, B.}, title = {Accurate Short-Circuit Current Measurements on Photovoltaic Modules - Challenges for On-site Outdoor Determinations}, series = {Proc. of 38th European Photovoltaic Solar Energy Conference and Exhibition (PVSEC), 4AV.2.6., September 2021, Lissabon}, booktitle = {Proc. of 38th European Photovoltaic Solar Energy Conference and Exhibition (PVSEC), 4AV.2.6., September 2021, Lissabon}, year = {2021}, language = {en} } @phdthesis{Schoepfer2019, author = {Sch{\"o}pfer, Fabian}, title = {Vibroacoustics of timber-frame structures excited by structure-borne sound sources}, school = {Technische Hochschule Rosenheim}, year = {2019}, abstract = {This thesis investigates the measurement and prediction of machinery noise in timber-frame buildings. To quantify the structure-borne sound power input from multi-point sources, simplified approaches were assessed that reduce the required data for out-of-plane force excitation. This identified approaches that give estimates within ±5 dB from 20 Hz to 2000 Hz. To investigative the importance of out-of-plane moment excitation, inverse methods were used to determine the power input; these were affected by noise but processing was used to overcome this shortcoming. A series of experimental investigations were carried out on a timber-frame structure undergoing mechanical point excitation. The driving-point mobility showed orthotropic plate characteristics at low frequencies, ribbed-plate characteristics in a narrow frequency band and infinite plate characteristics in mid- and high-frequency ranges. The moment mobility above or in-between studs was similar to infinite beam or plate theory with interpolation between these theories where necessary. The experimental work indicated the potential to use Statistical Energy Analysis (SEA) to predict sound transmission. The first experimental finding was that above the mass-spring-mass resonance frequency, the vibrational response of the wall leaves was uncorrelated. The second was a significant decrease in vibration across the wall from the excitation point, with structural intensity showing a decrease in net power flow across successive timber studs. The third was that tongue and groove connections between chipboard sheets significantly reduce the vibration transmission above 500 Hz. This led to different SEA models being used to model a timber-frame wall undergoing mechanical point excitation. A 41-subsystem model was found to be necessary to reproduce the measured vibration levels on both leaves within 10 dB. As there is a significant decrease in vibration with distance in the mid- and high-frequency range, the region close to the excitation point is particularly important and the SEA model has better accuracy in this region. An alternative engineering approach to the prediction of machinery noise in timber-frame buildings was introduced and validated that used measured transmission functions between the injected power and the spatial-average sound pressure level in a receiving room. A field survey and case studies indicate this is a feasible and practical approach.}, language = {en} } @article{MagniOchsdeVriesetal.2021, author = {Magni, Mara and Ochs, Fabian and de Vries, Samuel and Maccarini, Alessandro and Sigg, Ferdinand}, title = {Detailed cross comparison of building energy simulation tools results using a reference office building as a case study}, series = {Energy and Buildings}, volume = {250}, journal = {Energy and Buildings}, pages = {111260}, year = {2021}, abstract = {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.}, language = {en} } @article{FrescuraLeeSchoepferetal.2021, author = {Frescura, Alessia and Lee, Pyoung Jik and Sch{\"o}pfer, Fabian and Schanda, Ulrich}, title = {Correlations between standardised and real impact sound sources in lightweight wooden structures}, series = {Applied Acoustics}, volume = {173}, journal = {Applied Acoustics}, pages = {107690}, year = {2021}, abstract = {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.}, language = {en} } @article{SchaefleKautz2021, author = {Sch{\"a}fle, Claudia and Kautz, Christian}, title = {Student reasoning in hydrodynamics: Bernoulli's principle versus the continuity equation}, series = {Physical Review Physics Education Research}, volume = {17}, journal = {Physical Review Physics Education Research}, number = {1}, publisher = {American Physical Society}, pages = {010147}, year = {2021}, abstract = {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.}, language = {en} }