@article{AlsaadHartmannVoelker, author = {Alsaad, Hayder and Hartmann, Maria and Voelker, Conrad}, title = {The effect of a living wall system designated for greywater treatment on the hygrothermal performance of the facade}, series = {Energy and Buildings}, volume = {2022}, journal = {Energy and Buildings}, number = {volume 255, article 111711}, doi = {10.1016/j.enbuild.2021.111711}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20240116-65299}, pages = {17}, abstract = {Besides their multiple known benefits regarding urban microclimate, living walls can be used as decentralized stand-alone systems to treat greywater locally at the buildings. While this offers numerous environmental advantages, it can have a considerable impact on the hygrothermal performance of the facade as such systems involve bringing large quantities of water onto the facade. As it is difficult to represent complex entities such as plants in the typical simulation tools used for heat and moisture transport, this study suggests a new approach to tackle this challenge by coupling two tools: ENVI-Met and Delphin. ENVI-Met was used to simulate the impact of the plants to determine the local environmental parameters at the living wall. Delphin, on the other hand, was used to conduct the hygrothermal simulations using the local parameters calculated by ENVI-Met. Four wall constructions were investigated in this study: an uninsulated brick wall, a precast concrete plate, a sandy limestone wall, and a double-shell wall. The results showed that the living wall improved the U-value, the exterior surface temperature, and the heat flux through the wall. Moreover, the living wall did not increase the risk of moisture in the wall during winter and eliminated the risk of condensation.}, subject = {Feuchteleitung}, language = {en} } @article{PollackLueckWolfetal., author = {Pollack, Moritz and L{\"u}ck, Andrea and Wolf, Mario and Kraft, Eckhard and V{\"o}lker, Conrad}, title = {Energy and Business Synergy: Leveraging Biogenic Resources from Agriculture, Waste, and Wastewater in German Rural Areas}, series = {Sustainability}, volume = {2023}, journal = {Sustainability}, number = {volume 15, issue 24, article 16573}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/su152416573}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20231222-65172}, pages = {1 -- 25}, abstract = {The imperative to transform current energy provisions is widely acknowledged. However, scant attention has hitherto been directed toward rural municipalities and their innate resources, notably biogenic resources. In this paper, a methodological framework is developed to interconnect resources from waste, wastewater, and agricultural domains for energy utilization. This entails cataloging existing resources, delineating their potential via quantitative assessments utilizing diverse technologies, and encapsulating them in a conceptual model. The formulated models underwent iterative evaluation with engagement from diverse stakeholders. Consequently, 3 main concepts, complemented by 72 sub-concepts, were delineated, all fostering positive contributions to climate protection and providing heat supply in the rural study area. The outcomes' replicability is underscored by the study area's generic structure and the employed methodology. Through these inquiries, a framework for the requisite energy transition, with a pronounced emphasis on the coupling of waste, wastewater, and agriculture sectors in rural environments, is robustly analyzed.}, subject = {Energiewende}, language = {en} } @article{VogelArnoldVoelkeretal., author = {Vogel, Albert and Arnold, J{\"o}rg and Voelker, Conrad and Kornadt, Oliver}, title = {Data for sound pressure level prediction in lightweight constructions caused by structure-borne sound sources and their uncertainties}, series = {Data in Brief}, volume = {2023}, journal = {Data in Brief}, number = {Volume 48, June 2023, article 109292}, publisher = {Elsevier}, address = {Amsterdam}, doi = {10.1016/j.dib.2023.109292}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230719-64114}, pages = {1 -- 16}, abstract = {When predicting sound pressure levels induced by structure-borne sound sources and describing the sound propagation path through the building structure as exactly as possible, it is necessary to characterize the vibration behavior of the structure-borne sound sources. In this investigation, the characterization of structure-borne sound sources was performed using the two-stage method (TSM) described in EN 15657. Four different structure-borne sound sources were characterized and subsequently installed in a lightweight test stand. The resulting sound pressure levels in an adjacent receiving room were measured. In the second step, sound pressure levels were predicted according to EN 12354-5 based on the parameters of the structure-borne sound sources. Subsequently, the predicted and the measured sound pressure levels were compared to obtain reliable statements on the achievable accuracy when using source quantities determined by TSM with this prediction method.}, subject = {Bauakustik}, language = {en} } @phdthesis{Dokhanchi, author = {Dokhanchi, Najmeh Sadat}, title = {Measurement of the Indoor Air Temperature Distribution using Acoustic Travel-Time Tomography}, isbn = {978-3-00-075344-2 (print)}, doi = {10.25643/bauhaus-universitaet.4956}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230414-49567}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {155}, abstract = {One of the main criteria determining the thermal comfort of occupants is the air temperature. To monitor this parameter, a thermostat is traditionally mounted in the indoor environment for instance in office rooms in the workplaces, or directly on the radiator or in another location in a room. One of the drawbacks of this conventional method is the measurement at a certain location instead of the temperature distribution in the entire room including the occupant zone. As a result, the climatic conditions measured at the thermostat point may differ from those at the user's location. This not only negatively impacts the thermal comfort assessment but also leads to a waste of energy due to unnecessary heating and cooling. Moreover, for measuring the distribution of the air temperature under laboratory conditions, multiple thermal sensors should be installed in the area under investigation. This requires high effort in both installation and expense. To overcome the shortcomings of traditional sensors, Acoustic travel-time TOMography (ATOM) offers an alternative based on measuring the transmission sound velocity signals. The basis of the ATOM technique is the first-order dependency of the sound velocity on the medium's temperature. The average sound velocity, along the propagation paths, can be determined by travel-times estimation of a defined acoustic signal between transducers. After the travel-times collection, the room is divided into several volumetric grid cells, i.e. voxels, whose sizes are defined depending on the dimension of the room and the number of sound paths. Accordingly, the spatial air temperature in each voxel can be determined using a suitable tomographic algorithm. Recent studies indicate that despite the great potential of this technique to detect room climate, few experiments have been conducted. This thesis aims to develop the ATOM technique for indoor climatic applications while coupling the analysis methods of tomography and room acoustics. The method developed in this thesis uses high-energy early reflections in addition to the direct paths between transducers for travel time estimation. In this way, reflections can provide multiple sound paths that allow the room coverage to be maintained even when a few or even only one transmitter and receiver are used. In the development of the ATOM measurement system, several approaches have been employed, including the development of numerical methods and simulations and conducting experimental measurements, each of which has contributed to the improvement of the system's accuracy. In order to effectively separate the early reflections and ensure adequate coverage of the room with sound paths, a numerical method was developed based on the optimization of the coordinates of the sound transducers in the test room. The validation of the optimal positioning method shows that the reconstructed temperatures were significantly improved by placing the transducers at the optimal coordinates derived from the developed numerical method. The other numerical method developed is related to the selection of the travel times of the early reflections. Accordingly, the detection of the travel times has been improved by adjusting the lengths of the multiple analysis time-windows according to the individual travel times in the reflectogram of the room impulse response. This can reduce the probability of trapping faulty travel times in the analysis time-windows. The simulation model used in this thesis is based on the image source model (ISM) method for simulating the theoretical travel times of early reflection sound paths. The simulation model was developed to simulate the theoretical travel times up to third-order reflections. The empirical measurements were carried out in the climate lab of the Chair of Building Physics under different boundary conditions, i.e., combinations of different room air temperatures under both steady-state and transient conditions, and different measurement setups. With the measurements under controllable conditions in the climate lab, the validity of the developed numerical methods was confirmed. In this thesis, the performance of the ATOM measurement system was evaluated using two measurement setups. The setup for the initial investigations consists of an omnidirectional receiver and a near omnidirectional sound source, keeping the number of transducers as few as possible. This has led to accurately identify the sources of error that could occur in each part of the measuring system. The second measurement setup consists of two directional sound sources and one omnidirectional receiver. This arrangement of transducers allowed a higher number of well-detected travel times for tomography reconstruction, a better travel time estimation due to the directivity of the sound source, and better space utilization. Furthermore, this new measurement setup was tested to determine an optimal selection of the excitation signal. The results showed that for the utilized setup, a linear chirp signal with a frequency range of 200 - 4000 Hz and a signal duration of t = 1 s represents an optimal selection with respect to the reliability of the measured travel times and higher signal-to-noise ratio (SNR). To evaluate the performance of the measuring setups, the ATOM temperatures were always compared with the temperatures of high-resolution NTC thermistors with an accuracy of ±0.2 K. The entire measurement program, including acoustic measurements, simulation, signal processing, and visualization of measurement results are performed in MATLAB software. In addition, to reduce the uncertainty of the positioning of the transducers, the acoustic centre of the loudspeaker was determined experimentally for three types of excitation signals, namely MLS (maximum length sequence) signals with different lengths and duration, linear and logarithmic chirp signals with different defined frequency ranges. For this purpose, the climate lab was converted into a fully anechoic chamber by attaching absorption panels to the entire surfaces of the room. The measurement results indicated that the measurement of the acoustic centre of the sound source significantly reduces the displacement error of the transducer position. Moreover, to measure the air temperature in an occupied room, an algorithm was developed that can convert distorted signals into pure reference signals using an adaptive filter. The measurement results confirm the validity of the approach for a temperature interval of 4 K inside the climate lab. Accordingly, the accuracy of the reconstructed temperatures indicated that ATOM is very suitable for measuring the air temperature distribution in rooms.}, subject = {Bauphysik}, language = {en} } @article{AlsaadSchaelteSchneeweissetal., author = {Alsaad, Hayder and Sch{\"a}lte, Gereon and Schneeweiß, Mario and Becher, Lia and Pollack, Moritz and Gena, Amayu Wakoya and Schweiker, Marcel and Hartmann, Maria and Voelker, Conrad and Rossaint, Rolf and Irrgang, Matthias}, title = {The Spread of Exhaled Air and Aerosols during Physical Exercise}, series = {Journal of Clinical Medicine}, volume = {2023}, journal = {Journal of Clinical Medicine}, number = {Volume 12, issue 4, article 1300}, publisher = {Basel}, address = {MDPI}, doi = {10.3390/jcm12041300}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230208-49262}, pages = {20}, abstract = {Physical exercise demonstrates a special case of aerosol emission due to its associated elevated breathing rate. This can lead to a faster spread of airborne viruses and respiratory diseases. Therefore, this study investigates cross-infection risk during training. Twelve human subjects exercised on a cycle ergometer under three mask scenarios: no mask, surgical mask, and FFP2 mask. The emitted aerosols were measured in a grey room with a measurement setup equipped with an optical particle sensor. The spread of expired air was qualitatively and quantitatively assessed using schlieren imaging. Moreover, user satisfaction surveys were conducted to evaluate the comfort of wearing face masks during training. The results indicated that both surgical and FFP2 masks significantly reduced particles emission with a reduction efficiency of 87.1\% and 91.3\% of all particle sizes, respectively. However, compared to surgical masks, FFP2 masks provided a nearly tenfold greater reduction of the particle size range with long residence time in the air (0.3-0.5 μm). Furthermore, the investigated masks reduced exhalation spreading distances to less than 0.15 m and 0.1 m in the case of the surgical mask and FFP2 mask, respectively. User satisfaction solely differed with respect to perceived dyspnea between no mask and FFP2 mask conditions.}, subject = {Sport}, language = {en} } @article{BecherVoelkerRodehorstetal., author = {Becher, Lia and V{\"o}lker, Conrad and Rodehorst, Volker and Kuhne, Michael}, title = {Background-oriented schlieren technique for two-dimensional visualization of convective indoor air flows}, series = {Optics and Lasers in Engineering}, volume = {2020}, journal = {Optics and Lasers in Engineering}, number = {Volume 134, article 106282}, doi = {https://doi.org/10.1016/j.optlaseng.2020.106282}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220810-46972}, pages = {9}, abstract = {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.}, subject = {Raumklima}, language = {en} } @inproceedings{HartmannAlsaadVoelker, author = {Hartmann, Maria and Alsaad, Hayder and V{\"o}lker, Conrad}, title = {Das Potential von Fassadenbegr{\"u}nungen zur Verringerung des W{\"a}rmeinseleffekts: Simulation eines Beispielquartiers}, series = {Bauphysiktage Kaiserslautern 2022}, booktitle = {Bauphysiktage Kaiserslautern 2022}, address = {Kaiserslautern}, isbn = {978-3-95974-176-7}, issn = {2363-8206}, doi = {10.25643/bauhaus-universitaet.4667}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220713-46676}, pages = {147-149}, abstract = {Die Auswirkungen einer Fassadenbegr{\"u}nung auf den W{\"a}rmeinseleffekt in Stuttgart wurde f{\"u}r eine Hitzeperiode numerisch simuliert und bewertet. Die Ergebnisse zeigten positive Auswirkungen innerhalb des Simulationsgebiets sowie eine geringe Fernwirkung auf benachbarte Stadtquartiere. Diese {\"A}nderungen k{\"o}nnen zur Verbesserung des thermischen Komforts im Außenraum beitragen. Eine reduzierte Temperatur der Außenoberfl{\"a}che f{\"u}hrt dar{\"u}ber hinaus auch zu einer geringeren Oberfl{\"a}chentemperatur der Wandinnenseite, welche die Innenraumtemperatur beeinflusst. Folglich kann die thermische Behaglichkeit auch im Innenraum erh{\"o}ht werden.}, subject = {Mikroklima}, language = {de} } @inproceedings{Dokhanchi, author = {Dokhanchi, Najmeh Sadat}, title = {Reconstruction of the indoor air temperature distribution using acoustic travel-time tomography}, editor = {Arnold, J{\"o}rg}, doi = {10.25643/bauhaus-universitaet.4659}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220622-46593}, abstract = {Acoustic travel-time tomography (ATOM) is being increasingly considered recently as a remote sensing methodology to determine the indoor air temperatures distribution. It employs the relationship between the sound velocities along sound-paths and their related travel-times through measured room-impulse-response (RIR). Thus, the precise travel-time estimation is of critical importance which can be performed by applying an analysis time-window method. In this study, multiple analysis time-windows with different lengths are proposed to overcome the challenge of accurate detection of the travel-times at RIR. Hence, the ATOM-temperatures distribution has been measured at the climate chamber lab of the Bauhaus-University Weimar. As a benchmark, the temperatures of NTC thermistors are compared to the reconstructed temperatures derived from the ATOM technique illustrating this technique can be a reliable substitute for traditional thermal sensors. The numerical results indicate that the selection of an appropriate analysis time-window significantly enhances the accuracy of the reconstructed temperatures distribution.}, subject = {Bauphysik}, language = {en} } @inproceedings{Dokhanchi, author = {Dokhanchi, Najmeh Sadat}, title = {Acoustic travel time tomography: Applicability of an array of directional sound sources}, editor = {Arnold, J{\"o}rg}, doi = {10.25643/bauhaus-universitaet.4658}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220622-46589}, abstract = {The technique of Acoustic travel-time TOMography (ATOM) allows for measuring the distribution of air temperatures throughout the entire room based on the determined sound-travel-times of early reflections, currently up to second order reflections. The number of detected early reflections in the room impulse response (RIR) which stands for the desired sound paths inside the room, has a significant impact on the resolution of reconstructed temperatures. This study investigates the possibility of utilizing an array of directional sound sources for ATOM measurements instead of a single omnidirectional loudspeaker used in the previous studies [1-3]. The developed measurement setup consists of two directional sound sources placed near the edge of the floor in the climate chamber of the Bauhaus-University Weimar and one omnidirectional receiver at center of the room near the ceiling. In order to compensate for the reduced number of sound paths when using directional sound sources, it is proposed to take high-energy early reflections up to third order into account. For this purpose, the simulated travel times up to third-order image sources were implemented in the image source model (ISM) algorithm, by which these early reflections can be detected effectively for air temperature reconstructions. To minimize the uncertainties of travel-times estimation due to the positioning of the sound transducers inside the room, measurements were conducted to determine the exact emitting point of the utilized sound source i.e. its acoustic center (AC). For these measurements, three types of excitation signals (MLS, linear and logarithmic chirp signals) with various frequency ranges were used considering that the acoustic center of a sound source is a frequency dependent parameter [4]. Furthermore, measurements were conducted to determine an optimum excitation signal based on the given condition of the ATOM measurement set-up which defines an optimum method for the RIR estimation correspondingly. Finally, the uncertainty of the measuring system utilizing an array of directional sound sources was analyzed.}, subject = {Bauphysik}, language = {en} } @inproceedings{AlsaadVoelker, author = {Alsaad, Hayder and V{\"o}lker, Conrad}, title = {Measuring and visualizing the flow supplied by personalized ventilation}, series = {Proceedings Book Roomvent 2020}, booktitle = {Proceedings Book Roomvent 2020}, address = {Turin, Italy}, doi = {10.25643/bauhaus-universitaet.4657}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220622-46573}, abstract = {This study investigates the flow supplied by personalized ventilation (PV) by means of anemometer measurements and schlieren visualization. The study was conducted using a thermal manikin to simulate a seated occupant facing a PV outlet. Air velocity was measured at multiple points in the flow field; the collected velocity values were used to calculate the turbulence intensity. Results indicated that PV was supplying air with low turbulence intensity that was able to penetrate the convective boundary layer of the manikin to supply clean air for inhalation. The convective boundary layer, however, obstructed the supplied flow and reduced its velocity by a total of 0.26 m/s. The PV flow preserved its value until about 10 cm from the face where velocity started to drop. Further investigations were conducted to test a PV diffuser with a relatively large outlet diameter (18 cm). This diffuser was developed using 3d-modelling and 3d-printing. The diffuser successfully distributed the flow over the larger outlet area. However, the supplied velocity and turbulence fields were not uniform across the section.}, subject = {Bel{\"u}ftung}, language = {en} }