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  • 1.
    Kabanshi, Alan
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Sandberg, Mats
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Entrainment and its Implications on Microclimate Ventilation Systems: Scaling the Velocity and Temperature Field of a Round Free Jet2019In: Indoor Air, ISSN 0905-6947, E-ISSN 1600-0668, Vol. 29, no 2, p. 331-346Article in journal (Refereed)
    Abstract [en]

    Research on microclimate ventilation systems, which mostly involve free jets, point to delivery of better ventilation in breathing zones. While the literature is comprehensive, the influence of contaminant entrainment in jet flows and its implications on the delivery of supplied air is not fully addressed. This paper present and discuss entrainment characteristics of a jet issued from a round nozzle (0.05 m diameter), in relation to ventilation, by exploring the velocity and temperature fields of the jet flow. The results show a trend suggesting that increasing the Reynolds number (Re) reduces ambient entrainment. As shown herein, about 30% concentration of ambient air entrained into the bulk jet flow at Re 2541 while Re 9233 had about 13% and 19% for Re = 6537/12026 at downstream distance of 8 diameters (40 cm). The study discusses that “moderate to high” Re may be ideal to reduce contaminant entrainment, but this is limited by delivery distance and possibly the risk of occupant discomfort. Incorporating the entrainment mixing factor (the ratio of room contaminants entrained into a jet flow) in performance measurements is proposed and further studies are recommended to verify results herein and test whether this is general to other nozzle configurations.

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  • 2.
    Liu, Shichao
    et al.
    Center for the Built Environment, University of California, Berkeley, CA, USA.
    Schiavon, Stefano
    Center for the Built Environment, University of California, Berkeley, CA, USA.
    Kabanshi, Alan
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Nazaroff, William W
    Department of Civil and Environmental Engineering, University of California, Berkeley, CA, USA.
    Predicted Percentage Dissatisfied with Ankle Draft2017In: Indoor Air, ISSN 0905-6947, E-ISSN 1600-0668, Vol. 27, no 4, p. 852-862Article in journal (Refereed)
    Abstract [en]

    Draft is unwanted local convective cooling. The draft risk model of Fanger et al. (Energy and Buildings 12, 21-39, 1988) estimates the percentage of people dissatisfied with air movement due to overcooling at the neck. There is no model for predicting draft at ankles, which is more relevant to stratified air distribution systems such as underfloor air distribution (UFAD) and displacement ventilation (DV). We developed a model for predicted percentage dissatisfied with ankle draft (PPDAD ) based on laboratory experiments with 110 college students. We assessed the effect on ankle draft of various combinations of air speed (nominal range: 0.1-0.6 m/s), temperature (nominal range: 16.5-22.5 °C), turbulence intensity (at ankles), sex, and clothing insulation (< 0.7 clo; lower legs uncovered and covered). The results show that whole body thermal sensation and air speed at ankles are the dominant parameters affecting draft. The seated subjects accepted a vertical temperature difference of up to 8 °C between ankles (0.1 m) and head (1.1 m) at neutral whole body thermal sensation, 5 °C more than the maximum difference recommended in existing standards. The developed ankle draft model can be implemented in thermal comfort and air diffuser testing standards.

  • 3.
    Smedje, Greta
    et al.
    Uppsala University.
    Mattsson, Magnus
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.
    Wålinder, Robert
    Uppsala University.
    Comparing mixing and displacement ventilation in classrooms: pupils' perception and health2011In: Indoor Air, ISSN 0905-6947, E-ISSN 1600-0668, Vol. 21, no 6, p. 454-461Article in journal (Refereed)
    Abstract [en]

    Several studies have found that indoor air quality (IAQ) in schools is often poor and may affect the health of the pupils. Building ventilation is a means to reduce pollutant indoors but different designs should be evaluated for their effectiveness in different environments. In a field experiment performed in four classrooms in one school building we alternately supplied the air according to the mixing and displacement mode and collected information on exposures, pupils’ perception of IAQ and climate, health symptoms and performed clinical examinations. At breathing height, room temperature, relative humidity and the concentration of CO2 and cat allergen were similar in the periods with each ventilation type. The children perceived indoor air quality as similar in the two ventilation regimes, and there were few differences in symptom reports or clinical parameters. However, the pupils reported more eye symptoms during displacement ventilation.

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