TY - JOUR A1 - Becher, Lia A1 - Völker, Conrad A1 - Rodehorst, Volker A1 - Kuhne, Michael T1 - Background-oriented schlieren technique for two-dimensional visualization of convective indoor air flows JF - Optics and Lasers in Engineering N2 - This article focuses on further developments of the background-oriented schlieren (BOS) technique to visualize convective indoor air flow, which is usually defined by very small density gradients. Since the light rays deflect when passing through fluids with different densities, BOS can detect the resulting refractive index gradients as integration along a line of sight. In this paper, the BOS technique is used to yield a two-dimensional visualization of small density gradients. The novelty of the described method is the implementation of a highly sensitive BOS setup to visualize the ascending thermal plume from a heated thermal manikin with temperature differences of minimum 1 K. To guarantee steady boundary conditions, the thermal manikin was seated in a climate laboratory. For the experimental investigations, a high-resolution DLSR camera was used capturing a large field of view with sufficient detail accuracy. Several parameters such as various backgrounds, focal lengths, room air temperatures, and distances between the object of investigation, camera, and structured background were tested to find the most suitable parameters to visualize convective indoor air flow. Besides these measurements, this paper presents the analyzing method using cross-correlation algorithms and finally the results of visualizing the convective indoor air flow with BOS. The highly sensitive BOS setup presented in this article complements the commonly used invasive methods that highly influence weak air flows. KW - Raumklima KW - Raumluftströmungen KW - Flow visualization KW - Convective indoor air flow KW - Background-oriented schlieren KW - Human thermal plume KW - Cross-correlation Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20220810-46972 N1 - This article is published by Elsevier in Optics and Lasers in Engineering 134 (2020) 106282 and may be found at https://doi.org/10.1016/j.optlaseng.2020.106282 Copyright © 2020 Elsevier Ltd. All rights reserved. This article may be downloaded for personal use only. Any other use requires prior permission of the authors and Elsevier Ltd. VL - 2020 IS - Volume 134, article 106282 ER - TY - JOUR A1 - Alsaad, Hayder A1 - Völker, Conrad T1 - Der Kühlungseffekt der personalisierten Lüftung T1 - The cooling effect of personalized ventilation systems JF - Bauphysik N2 - Personalisierte Lüftung (PL) kann die thermische Behaglichkeit sowie die Qualität der eingeatmeten Atemluft verbessern, in dem jedem Arbeitsplatz Frischluft separat zugeführt wird. In diesem Beitrag wird die Wirkung der PL auf die thermische Behaglichkeit der Nutzer unter sommerlichen Randbedingungen untersucht. Hierfür wurden zwei Ansätze zur Bewertung des Kühlungseffekts der PL untersucht: basierend auf (1) der äquivalenten Temperatur und (2) dem thermischen Empfinden. Grundlage der Auswertung sind in einer Klimakammer gemessene sowie numerisch simulierte Daten. Vor der Durchführung der Simulationen wurde das numerische Modell zunächst anhand der gemessenen Daten validiert. Die Ergebnisse zeigen, dass der Ansatz basierend auf dem thermischen Empfinden zur Evaluierung des Kühlungseffekts der PL sinnvoller sein kann, da bei diesem die komplexen physiologischen Faktoren besser berücksichtigt werden. N2 - Personalized ventilation (PV) can improve thermal comfort and inhaled air quality by supplying air to each workstation separately. This study investigates the impact of PV on the thermal state of the users under summer boundary conditions. Two approaches to evaluating the cooling effect of PV were investigated, based on equivalent temperature and based on thermal sensation. Both approaches implemented measured and simulated values of the cooling effect of PV. Before conducting the simulations, the numerical model was first validated against measured data collected in a climate chamber equipped with a thermal manikin. Results indicated that the thermal sensation approach can be more suitable for evaluating the cooling effect of PV due to the complex physiological factors it considers. KW - Lüftung KW - Strömung KW - Raumklima KW - Temperatur KW - personalized ventilation KW - computational fluid dynamics KW - Simulation KW - personalisierte Lüftung KW - äquivalente Temperatur KW - thermisches Empfinden Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20201020-42723 UR - https://onlinelibrary.wiley.com/doi/abs/10.1002/bapi.202000018 N1 - © 2020 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin. Dieser Artikel kann für den persönlichen Gebrauch heruntergeladen werden. Andere Verwendungen bedürfen der vorherigen Zustimmung der Autoren und des Verlags Ernst & Sohn. Der folgende Artikel erschien in der Bauphysik 42 (2020), Heft 5, 218-225, DOI: 10.1002/bapi.202000018 VL - 2020 IS - volume 42, issue 5 SP - 218 EP - 225 PB - Ernst & Sohn bei John Wiley & Sons CY - Hoboken ER - TY - JOUR A1 - Alsaad, Hayder A1 - Völker, Conrad T1 - Performance evaluation of ductless personalized ventilation in comparison with desk fans using numerical simulations JF - Indoor Air N2 - The performance of ductless personalized ventilation (DPV) was compared to the performance of a typical desk fan since they are both stand-alone systems that allow the users to personalize their indoor environment. The two systems were evaluated using a validated computational fluid dynamics (CFD) model of an office room occupied by two users. To investigate the impact of DPV and the fan on the inhaled air quality, two types of contamination sources were modelled in the domain: an active source and a passive source. Additionally, the influence of the compared systems on thermal comfort was assessed using the coupling of CFD with the comfort model developed by the University of California, Berkeley (UCB model). Results indicated that DPV performed generally better than the desk fan. It provided better thermal comfort and showed a superior performance in removing the exhaled contaminants. However, the desk fan performed better in removing the contaminants emitted from a passive source near the floor level. This indicates that the performance of DPV and desk fans depends highly on the location of the contamination source. Moreover, the simulations showed that both systems increased the spread of exhaled contamination when used by the source occupant. KW - Behaglichkeit KW - Raumklima KW - Strömungsmechanik KW - Fluid KW - computational fluid dynamics KW - desk fan KW - ductless personalized ventilation KW - IAQ KW - thermal comfort Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20200422-41407 UR - https://onlinelibrary.wiley.com/doi/full/10.1111/ina.12672 VL - 2020 PB - John Wiley & Sons Ltd ER - TY - JOUR A1 - Gena, Amayu Wakoya A1 - Völker, Conrad A1 - Settles, Gary T1 - Qualitative and quantitative schlieren optical measurement of the human thermal plume JF - Indoor Air N2 - A new large‐field, high‐sensitivity, single‐mirror coincident schlieren optical instrument has been installed at the Bauhaus‐Universität Weimar for the purpose of indoor air research. Its performance is assessed by the non‐intrusive measurement of the thermal plume of a heated manikin. The schlieren system produces excellent qualitative images of the manikin's thermal plume and also quantitative data, especially schlieren velocimetry of the plume's velocity field that is derived from the digital cross‐correlation analysis of a large time sequence of schlieren images. The quantitative results are compared with thermistor and hot‐wire anemometer data obtained at discrete points in the plume. Good agreement is obtained, once the differences between path‐averaged schlieren data and planar anemometry data are reconciled. KW - Raumklima KW - Behaglichkeit KW - Digital image correlation KW - human thermal plume KW - schlieren imaging KW - schlieren velocimetry KW - thermal comfort KW - Schlierenspiegel Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20200709-41936 UR - https://onlinelibrary.wiley.com/doi/full/10.1111/ina.12674 VL - 2020 IS - volume 30, issue 4 SP - 757 EP - 766 PB - John Wiley & Sons ER -