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- Fakultät für Angewandte Natur- und Geisteswissenschaften (17) (remove)
A quantitative physical model for potential induced degradation of the shunting type (PID-s) in solar modules is introduced. Based on a drift and diffusion approach for sodium ions and atoms, it gives insight into the kinetics of degradation and the corresponding regeneration. A simple drift/source term is used to describe the time-dependent flux of Na-ions towards stacking faults at the surface of the solar cell. The assumed transport mechanism for Na+ ions through the SiN-layer uses the modified Stern-Eyring rate theory but our approach can also be adapted to other mechanisms. Several PID-s and regeneration curves of one-cell solar modules at T = 49°C and T = 90°C with 1000V potential difference between modul frame and cell were measured and least-square fits of the in-situ measured parallel resistance Rsh to the model were performed giving very good accordance.
Based on a few measurements, the model can predict PID-s and regeneration characteristics of solar modules under different conditions.
A high-order finite element model for vibration analysis of cross-laminated timber assemblies
(2017)
The vibration behavior of cross-laminated timber components in the low-frequency range can be predicted with high accuracy by the finite element method. However, the modeling of assembled cross-laminated timber components has been studied only scarcely. The three-dimensional p-version of the finite element method, which is characterized by hierarchic high-order shape functions, is well suited to consider coupling and support conditions. Furthermore, a small number of degrees of freedom can be obtained in case of thin-walled structures using p-elements with high aspect ratios and anisotropic ansatz spaces. In this article, a model for cross-laminated timber assemblies made of volumetric high-order finite elements is presented. Two representative types of connections are investigated, one with an elastomer between the cross-laminated timber components and the other without. The model is validated, and suitable ranges for the stiffness parameters of the finite elements which represent the junctions are identified.
The objective of this research project is to develop a solar-powered refrigerator in the lower capacity range of up to 5 kW of cooling power. With the use of liquid pistons and one of the most efficient thermodynamic cycles known, the Stirling cycle, this product has the potential to outperform rival solar cooling technologies while providing inexpensive, reliable, quiet, environmentally-friendly, and efficient solar cooling for residential use, due to its straightforward manufacturing, simple design and inert working gas. Presented in this paper are the newest results of the theoretical and experimental investigation into deducing the key design parameters and system configuration of the so-called Liquid Piston Stirling Cooler (LPSC), which will help lead to optimal performance. Computer models of the complex unconstrained system have been constructed and validated using the modelling software Sage and shown to replicate system behavior with reasonable accuracy in experiments. The models have been used to predict system improvements and identify limitations imposed by the use of liquid pistons. The results to date provide a unique insight into a relatively little studied area in Stirling cycle research.
Outdoor performance analyses of photovoltaic modules can be advantageous compared to indoor investigations, as they take into account the influences of natural test conditions on the modules. However, such outdoor performance assessments usually suffer from poor accuracies due to undefined test conditions for the modules. This paper reports on a comprehensive concept for improved outdoor analysis which results in performance data with indoor laboratory precision. The approach delivers current-voltage characteristics for even more test conditions than required by the standard IEC 61853-1. Hence, curves of modules’ electrical parameters above irradiance can be deduced for any temperatures. The concept allows precise determination of temperature coefficients for user-defined irradiances taking into account outdoor effects like light-soaking or light-induced degradation. The calibration and measurement uncertainty of the presented outdoor analysis method is evaluated quantitatively. For the measurements an advanced outdoor set-up was used.
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
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.
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.
In der Diskussion um bezahlbares Bauen werden aktuell die Standards im Wohnungsbau hinterfragt, darunter auch die Schallschutzanforderungen. Die Wahrnehmung von Schallschutz ist subjektiv und wird von verschiedenen Faktoren wie Alter und individuellen Empfindlichkeiten beeinflusst. Nachbarschaftslärm kann zu Schlafstörungen und Belästigungen führen, während Verkehrslärm nachweislich Gesundheitsprobleme verursacht. Das Konzept „Einfach Bauen“ zielt darauf ab, das Bauen zu vereinfachen und nachhaltiger zu gestalten. Drei Forschungshäuser, die diesem Konzept folgen, wurden auf Schallschutz überprüft. Dabei erfüllten Wohnungstrennwände und -decken die Anforderungen. Die Untersuchung der Bewohnerzufriedenheit durch Befragungen in diesen Häusern zeigt, dass die Wahrnehmung von Lärm stark variiert. Die Zufriedenheit wird durch die Kommunikation mit den Nachbarn beeinflusst. Das Fallbeispiel verdeutlicht, dass Schallschutzanforderungen oft nicht den individuellen Lärmempfinden gerecht werden, da nicht-akustische Faktoren eine starke Rolle spielen. Die Erwartung eines reduzierten Schallschutzes bei „Einfach Bauen“ kann zu Fehlvorstellungen führen, wie der Auszug von Bewohnern aus Schallschutzgründen zeigt. Die derzeitigen Mindestanforderungen an den Schallschutz erweisen sich für sehr empfindsame Menschen als unzureichend. Es ist wichtig, dass die Bewohner über den zu erwartenden Schallschutz informiert werden, um ein harmonisches Zusammenleben zu ermöglichen.
Zielsetzung
In den letzten Jahren konnte eine Steigerung der Anzahl privater Krankenhäuser und Betten festgestellt werden. Die Probleme der Investitionsfinanzierung deutscher Krankenhäuser in Kombination mit verstärkenden Faktoren wie der Einführung der DRGs, aber auch die Erwartung einer höheren Effizienz nach der Privatisierung einer Klinik können als Hauptgründe bei Privatisierungsentscheidungen genannt werden. Es soll untersucht werden, wie ehemalige öffentliche Krankenhausträger den Erfolg der Privatisierung einschätzen.
Methodik
Alle 99 identifizierten ehemaligen öffentlichen Träger, die ihr Krankenhaus in den Jahren 2003–2013 an einen privaten Eigentümer verkauft hatten, wurden hinsichtlich ihrer Einschätzung von Zielen sowie Befürchtungen vor und nach der Privatisierung anonym und schriftlich befragt.
Ergebnisse und Schlussfolgerung
Zusammenfassend lässt sich feststellen, dass bei einer ausreichenden Finanzierung der Krankenhäuser aus Krankenkassenbeiträgen (Betriebsmittel) und Ländermittel (Investitionskosten) der Privatisierungsdruck rapide sinken würde. Wenn jedoch privatisiert wurde, hatte dies aus Sicht der ehemaligen Träger weder einen negativen Einfluss auf die medizinische Versorgung in der Region, noch auf die Qualität der medizinischen Behandlung und auf den Umgang mit den Mitarbeitern.
Die Einschätzungen der ehemaligen Träger weisen eine statistisch überprüfte Übereinstimmung auf. Die mit einer Privatisierung verbundenen Erwartungen und Ziele werden prinzipiell als erfüllt wahrgenommen
Wooden building systems, including cross-laminated timber elements, are becoming more common. The last few years have seen new developments and documentation of innovative types of cross-laminated timber floor assemblies. Regarding impact sound associated to walking persons, running or jumping children, such floor assemblies can be regarded as a weak part. So far, there are no reliable standardized calculation models available, for prediction of impact sound in the entire frequency range. Therefore the design is always based upon previous experiences and available measurements. This article presents the results of a number of well controlled sound insulation measurements of cross-laminated timber/massive wood floor constructions conducted in laboratories. The collection of data and results analysis highlight some basic phenomena. For instance, how structural differences related to the grouping of the constructions change the frequency distribution of the impact sound level and the single number quantities. Another significant result is the influence of the dynamic stiffness of the resilient interlayer of floating floor systems and the mass per unit area of the floors. Based on this analysis, the aim is to identify similarities and carry out simplifications. The data will be further processed and used in the development of prediction models and optimization process of cross-laminated timber floor assemblies.