1,720,992 research outputs found
Use of steady and intermittent personalized ventilation in indoor environments: Thermal comfort and Indoor air quality
Full text linkKamel Ghali; Nesreene Ghaddar; Fadl Moukalled; Fouad Azizi; Walid Chakroun; Arsen MelikovThe wellbeing and productivity of occupants in indoor spaces are correlated to their satisfaction with their thermal environment and their breathable air quality. This is highly dependent on the installation of carefully designed and energy-efficient air distribution systems such as personalized ventilation. These systems are individual devices consisting of a ducting network, which outlet delivers conditioned clean fresh air towards the occupant. As the issuing jet is adjustable in flow rate, direction and temperature, personalized ventilators respond to each occupant’s thermal preferences while improving the inhaled air quality compared to standalone total volume ventilation. Research on personalized ventilation has investigated its performance under steady state conditions. In other words, its adjustable operating conditions were constant over prolonged periods of time.
The first part of this work integrates for the first time, the concept of personalized ventilation with dynamic cooling, known to enhance comfort in warm indoor conditions. This is done by supplying the personalized flow rate in a time-dependent sinusoidal profile that fluctuates between a minimum and a maximum at frequencies of 0.3-1 Hz. The occupant is hence given additional freedom to adjust the jet frequency to their liking or revert to steady supply. This device is denoted as intermittent personalized ventilation. This work studies through experimentally validated CFD models, the performance of intermittent personalized ventilation in a space equipped with typical mixing ventilation and another equipped with a chilled ceiling, in enhancing occupants’ thermal comfort. Breathable air quality will also be assessed, and possible energy savings evaluated in comparison with a steady system. It was found that intermittent personalized ventilators enhanced thermal comfort especially in warm indoor conditions (26 C) with increasing frequency. It did not perform well in neutral conditions (24 C). Moreover, due to increased jet turbulence, it provided lower, but nonetheless satisfactory breathable air quality compared to steady personalized ventilation. Energy savings of 16% and 8% were achieved in the case of mixing ventilation and chilled ceiling.
Personalized ventilation has always been viewed as a means to improve indoor quality for the person using it by reducing exposure to gaseous or particulate matter pollutants. However, in the presence of particle emissions, personalized ventilation can contribute to particle deposition on occupants’ clothing, which can act as subsequent sources if triggered by occupants’ physical activities. Hence, personalized ventilation can contribute to second-hand clothing-mediated exposures. This work also investigates through experimentally validated CFD models the effect of different air terminal devices in reducing inhalation exposure while contributing to second-hand clothing exposure. Results showed that a computer mounted panel showed the best performance as it simultaneously decreased all types of exposure. Vertical desk grills decreased inhalation exposure while having negligible effect on second-hand exposure. Round movable panels decreased inhalation exposure but significantly increased clothing mediated exposures
High-Resolution Indoor Environmental Dataset from a Living Lab with Personalized Environmental Control Systems (PECS)
No full textThe building sector faces growing challenges in balancing energy efficiency with occupant comfort, especially amid climate change, air pollution, and post-pandemic demands on HVAC systems. Personalized Environmental Control Systems (PECS) offer a promising solution by allowing individuals to control their immediate environment (e.g., temperature, air quality), thereby enabling energy savings without sacrificing comfort. Despite their proven benefits, PECS have seen limited market adoption due to the lack of standardized performance evaluation methods and benchmark data.
Computational Fluid Dynamics (CFD) is commonly used to study PECS, but creating accurate CFD models is resource-intensive and requires detailed experimental validation—something many researchers struggle to provide due to limited infrastructure. Currently, only one known benchmark dataset exists, which is not representative of real-world settings.
To address this gap, the current work presents a high-resolution dataset of indoor environmental measurements (air velocity, temperature, and CO₂) from a living lab designed to simulate an open-plan office. The dataset, detailed in an accompanying Excel file, supports the creation and validation of CFD models for spaces equipped with various ventilation setups, including standalone systems and PECS configurations
Resilient passive cooling strategies during heat waves:A quantitative assessment in different climates
Full text linkThe frequency and severity of extreme weather events like heat waves are rising, posing significant challenges for buildings and their cooling systems. To safeguard occupants from potentially hazardous indoor temperatures, buildings and their cooling systems must be designed and managed to withstand these conditions and thus be resilient. This study assessed via building simulations the resilience performance of selected individual passive cooling strategies for five different climates (ASHRAE climate zones 2A, 3A, 3B, 4A, and 6A) and three heatwave periods (historical, future mid-term and future long-term). Resilience performance was assessed with three criteria: heatwave impact (°C·h above a reference standard effective temperature), absorptivity rate (°C/h), and recovery rate (°C/h). Strategies such as solar shading, cool envelope materials, advanced glazing, and ventilative cooling could each reduce the heat wave impact and the absorptivity rates in all studied climates at different levels of efficiency. As the heat waves became more extreme, the performance declined at different rates depending on the climate. Some strategies were more suited to specific climates such as cool envelope materials in climate 2A. Most strategies could not speed up the recovery rates from the heat waves except for ventilative cooling in climate 3B. With careful design to maximize the benefits of favorable wind conditions, every climate could benefit from ventilative cooling strategies to speed up recovery from heat waves
Particle release and transport from human skin and clothing: A CFD modeling methodology
Full text linkParticle release from human skin and clothing has been identified as an important contributor to particulate matter burden indoors. However, knowledge about modeling the coarse particle release from skin and clothing is limited. This study developed a new empirically validated CFD modeling methodology for particle release and transport from seated occupants in an office setting. We tested three modeling approaches for particle emissions: Uniform; Uniform + Localized; and Uniform + Localized with Body Motion; applied to four office scenarios involving a single occupant and two occupants facing each other at 1- and 2-m distances. Uniform particle emissions from skin and clothing underpredicted personal inhalation exposure by as much as 55%-80%. Combining uniform with localized emissions from the armpits drastically reduced the error margin to <10%. However, this modeling approach heavily underestimated particle mass exchange (cross-contamination) between the occupants. Accounting for the occupant's body motion-by applying the momentum theory method-yielded the most accurate personal exposure and cross-contamination results, with errors below 12%. The study suggests that for accurate modeling of particle release and transport from seated occupants indoors, localized body emissions in combination with simplified bodily movements need to be taken into account.status: Publishe
Particle release and transport from human skin and clothing: A CFD modeling methodology
No full textParticle release from human skin and clothing has been identified as an important contributor to particulate matter burden indoors. However, knowledge about modeling the coarse particle release from skin and clothing is limited. This study developed a new empirically validated CFD modeling methodology for particle release and transport from seated occupants in an office setting. We tested three modeling approaches for particle emissions: Uniform; Uniform + Localized; and Uniform + Localized with Body Motion; applied to four office scenarios involving a single occupant and two occupants facing each other at 1- and 2-m distances. Uniform particle emissions from skin and clothing underpredicted personal inhalation exposure by as much as 55%-80%. Combining uniform with localized emissions from the armpits drastically reduced the error margin to <10%. However, this modeling approach heavily underestimated particle mass exchange (cross-contamination) between the occupants. Accounting for the occupant's body motion-by applying the momentum theory method-yielded the most accurate personal exposure and cross-contamination results, with errors below 12%. The study suggests that for accurate modeling of particle release and transport from seated occupants indoors, localized body emissions in combination with simplified bodily movements need to be taken into account.HOBE
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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