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  • 1.
    Arghand, Taha
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Karimipanah, Taghi
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Awbi, Hazim
    School of Construction Management and Engineering, University of Reading, United Kingdom.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Larsson, Ulf
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Linden, Elisabet
    University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory. University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory.
    An experimental investigation of the flow and comfort parameters for under-floor, confluent jets and mixing ventilation systems in an open-plan office2015In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 92, p. 48-60Article in journal (Refereed)
    Abstract [en]

    There is a new trend to convert the workplaces from individual office rooms to open offices for motivating money saving and better communication. With such a shift the ability of existing ventilation systems in meeting the new requirements is a challenging question for researchers. The available options could have an impact on workers' health in terms of providing acceptable levels of thermalcomfort and indoor air quality. Thus, this experimental investigation focuses on the performances of three different air distribution systems in an open-plan office space. The investigated systems were: mixing ventilation with ceiling-mounted inlets, confluent jets ventilation and underfloor air distribution with straight and curved vanes. Although this represents a small part of our more extensiveexperimental investigation, the results show that all the purposed stratified ventilation systems (CJV and UFAD) were more or less behaving as mixing systems with some tendency for displacement effects. Nevertheless, it is known that the mixing systems have a stable flow pattern but has the disadvantage of mixing contaminated air with the fresh supplied air which may produce lower performance and in worst cases occupants' illness. For the open-plan office we studied here, it will be shown that the new systems are capable of performing better than the conventional mixing systems. As expected, the higher air exchange efficiency in combination with lower local mean age of air for corner-mounted CJV and floor-mounted UFAD grills systems indicates that these systems are suitable for open-plan offices and are to be favored over conventional mixing systems.

  • 2.
    Chen, Lan
    et al.
    School of Amopheric Sciences, Sun Yat-sen University, HaiZhu, Guangzhou, China.
    Hang, Jian
    School of Amopheric Sciences, Sun Yat-sen University, HaiZhu, Guangzhou, China.
    Sandberg, Mats
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Claesson, Leif
    University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory.
    Di Sabatino, Silvana
    Department of Physics and Astronomy - DIFA, ALMA MATER STUDIORUM - University of Bologna, Bologna, Italy.
    The Influence of Building Packing Densities on Flow Adjustment and City Breathability in Urban-like Geometries2017In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 198, p. 758-769Article in journal (Refereed)
    Abstract [en]

    City breathability refers to the air exchange process between the flows above and within urban canopy layers (UCL) and that of in-canopy flow, measuring the potential of wind to remove and dilute pollutants, heat and other scalars in a city. Bulk flow parameters such as in-canopy velocity (Uc) and exchange velocity (UE) have been applied to evaluate the city breathability. Both wind tunnel experiments and computational fluid dynamics (CFD) simulations were used to study the flow adjustment and the variation of city breathability through urban-like models with different building packing densities. We experimentally studied some 25-row and 15-column aligned cubic building arrays (the building width B=72 mm and building heights H=B) in a closed-circuit boundary layer wind tunnel. Effect of building packing densities (λp=λf=0.11, 0.25, 0.44) on flow adjustment and drag force of each buildings were measured. Wind tunnel data show that wind speed decreases quickly through building arrays due to strong building drag. The first upstream building induces the strongest flow resistance. The flow adjustment length varies slightly with building packing densities. Larger building packing density produces lower drag force by individual buildings and attains smaller velocity in urban canopy layers, which causes weaker city breathability capacity. In CFD simulations, we performed seven test cases with various building packing densities of λp=λf=0.0625, 0.11, 0.25, 0.36, 0.44 and 0.56. In the cases of λp=λf=0.11, 0.25, 0.44, the simulated profiles of velocity and drag force agree with experiment data well. We computed Uc and UE, which represent horizontal and vertical ventilation capacity respectively. The inlet velocity at 2.5 times building height in the upstream free flow is defined as the reference velocity Uref. Results show that UE/Uref changes slightly (1.1% to 0.7%) but Uc/Uref significantly decreases from 0.4 to 0.1 as building packing densities rise from 0.0625 to 0.56. Although UE is induced by both mean flows and turbulent momentum flux across the top surface of urban canopy, vertical turbulent diffusion is found to contribute mostly to UE.

  • 3.
    Chen, Lan
    et al.
    School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou, PR China.
    Hang, Jian
    School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou, PR China; Institute of Earth Climate and Environment System, Sun Yat-sen University, Guangzhou, PR China.
    Sandberg, Mats
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Claesson, Leif
    University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory.
    Di Sabatino, Silvana
    University of Bologna, Bologna, Italy.
    Wigö, Hans
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    The impacts of building height variations and building packing densities on flow adjustment and city breathability in idealized urban models2017In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 118, p. 344-361Article in journal (Refereed)
    Abstract [en]

    Improving city breathability has been confirmed as one feasible measure to improve pollutant dilution in the urban canopy layer (UCL). Building height variability enhances vertical mixing, but its impacts remain not completely explored. Therefore, both wind tunnel experiments and computational fluid dynamic (CFD) simulations are used to investigate the effect of building height variations (six height standard deviations σH = 0%–77.8%) associated to building packing densities namely λp/λf = 0.25/0.375 (medium-density) and 0.44/0.67 (compact) on city breathability. Two bulk variables (i.e. the in-canopy velocity (UC) and exchange velocity (UE)) are adopted to quantify the horizontal and vertical city breathability respectively, which are normalized by the reference velocity (Uref) in the free flow, typically set at z = 2.5H0 where H0 is the mean building height. Both flow quantities and city breathability experience a flow adjustment process, then reach a balance. The adjustment distance is at least three times longer than four rows documented in previous literature. The medium-density arrays experience much larger UC and UE than the compact ones. UE is found mainly induced by vertical turbulent fluxes, instead of vertical mean flows. In height-variation cases, taller buildings experience larger drag force and city breathability than lower buildings and those in uniform-height cases. For medium-density and compact models with uniform height, the balanced UC/Uref are 0.124 and 0.105 respectively, moreover the balanced UE/Uref are 0.0078 and 0.0065. In contrast, the average UC/Uref in height-variation cases are larger (115.3%–139.5% and 125.7%–141.9% of uniform-height cases) but UE/Uref are smaller (74.4%–79.5% and 61.5%–86.2% of uniform-height cases) for medium-density and compact models. 

  • 4.
    Claesson, Leif
    University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory.
    Kartläggning av vindförhållanden på Gävle Strand: Modellprov utförda i vindtunnel vid Akademin för Teknik och Miljö, Högskolan i Gävle2018Report (Other academic)
  • 5.
    Kabanshi, Alan
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Sattari, Amir
    School of Technology and Business Studies, Dalarna University, Sweden.
    Linden, Elisabet
    University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory.
    Wigö, Hans
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Sandberg, Mats
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Experimental study on contaminant entrainment in air distribution systems with free jets2017In: Healthy Buildings 2017 - Europe, ISIAQ , 2017, article id 0040Conference paper (Refereed)
    Abstract [en]

    This is a preliminary study to an ongoing experimental and theoretical study of ambient entrainment of room air into axisymmetric free jets. The study herein aims to understanding characteristic behaviour of free jets, especially in low mixing ventilation technologies in order to get the best of such applications. In this paper, we explore the interaction of a free jet and its ambient, the effect on jet development, characteristics and behaviour at different Reynold numbers. Measurements were done with Particle Image Velocimetry (PIV) under isothermal conditions. As shown, at lower Reynolds numbers the jet is mostly laminar but is unstable consequently shortening the penetration distance into the ambient. As the Reynolds numbers increase the instability reduces and the penetration distance increases, but entrainment increases as vortices are generated closer to the nozzle exit. The current study suggests that’s further investigation is needed to define limits within which low and high mixing can be achieved with free jets, as this will have practical implications on optimization and implementation of free jets.

  • 6.
    Lundström, Hans
    University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory.
    Improving long-term stability of hot-wire anemometer sensors by means of annealing2015In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 86, no 8, article id 086104Article in journal (Refereed)
    Abstract [en]

    Annealing procedures for hot-wire sensors of platinum and platinum-plated tungsten have been investigated experimentally. It was discovered that the two investigated sensor metals behave quite differently during the annealing process, but for both types annealing may improve long-term stability considerably. Measured drift of sensors both without and with prior annealing is presented. Suggestions for suitable annealing temperatures and times are given. 

  • 7.
    Mattsson, Magnus
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Linden, Elisabet
    University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory.
    Test av luftrenare i Visby domkyrka2016Report (Other academic)
    Abstract [sv]

    Efter den senaste renoveringen av Visby domkyrka, som bl a innefattade rengöring av innerväggar (våren 2014), noterades en oväntat snabb försmutsning av rengjorda väggytor, orsakad av avsättning av partiklar i inneluften. Med syfte att minska försmutsningstakten installerades två fristående luftrenare av elektrostatisk modell i kyrkan i oktober 2015. Föreliggande studie har haft som främsta syfta att utvärdera dessa luftrenares effektivitet i att rena inneluften på luftburna partiklar, framför allt från levande ljus. Utvärderingen har gjorts genom att mäta hur partikelhalten i kyrksalen förändrades vid olika driftfall på luftrenarna. Två olika flödesinställningar på luftrenarna provades: maxflöde resp. lågflöde, där maxflödet provades med både horisontellt och vertikalt riktat utblås av den renade luften. Anledningen till att även ett lägre luftreningsflöde provades var att luftrenarna bullrade så mycket vid maxflöde att detta driftförhållande endast torde bli aktuellt utanför besökstid. Studien har även inkluderat luftomsättningsmätning med spårgasteknik, luft- och yttemperaturmätningar, samt kallrasmätning vid vägg. Även ett vädringstest via portöppning har ingått. 

    Resultaten tyder på att luftrenarna har en klart renande effekt avseende luftburna partiklar i kyrksalen. Den minskning i antalet partiklar som luftrenarna åstadkom (partikelrenings-effektiviteten) varierade emellertid med partikelstorleken. I lågflödesfallet erhölls en reduktion av de minsta partiklarna (ultrafina, 0,02-0,3 µm) med ca 31 %, medan den för större partiklar (0,3-10 µm) var av storleksordningen 65‑75 %. I maxflödesfallet blev motsvarande siffror ca 58 % för de minsta partiklarna och 80‑90 % för de större. I välbesökta kyrkor där levande ljus ofta tänds – som i Visby domkyrka – utgör emissionerna från ljusen förmodligen den största partikelkällan. För dessa tycks de minsta partiklarna dominera avseende partikelyta (som kan tänkas täcka/försmutsa invändiga ytor), varför den sammantagna partikelreningseffektiviteten avseende försmutsning hamnar närmare den för de minsta partiklarna. Det är dock troligt att partikelreningseffektivitet blir något högre sommartid, då de riktigt stora besökarskarorna kommer i fallet Visby domkyrka.

    Riktningen på utblåset på luftrenarna hade ingen nämnvärd inverkan på partikelrenings-effektiviteten. Dock indikerade mätningarna av kallras (nedfallande luft) längs yttervägg i kyrkan att detta blir något större vid uppåtriktat utblås på luftrenarna, vilket riskerar att öka partikelavsättningstakten vid ytan. Detta fenomen behöver dock studeras närmare. Testet med vädring genom portöppning indikerade att ett avsevärt luftutbyte erhölls med denna metod, och att tillfällig vädring därför kan vara en lämplig åtgärd (även som komplement till luftrenare) vid tillfällen med många besökare och/eller mycket ljusbränning. Både partikel- och spårgasmätningarna påvisade god luftomblandning i kyrksalen, vilket är positivt för spridningen av den renade luften, och detta bidrar till att placeringen av luftrenarna är mindre kritisk. Sommartid kan dock luftomblandningen bli sämre; detta kan behöva undersökas närmare. Förutom minskad försmutsning kan luftrenarna förväntas bidra till en hälsosammare innemiljö ett minskat städbehov i kyrkan.

  • 8.
    Sandberg, Mats
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Mattsson, Magnus
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Wigö, Hans
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Hayati, Abolfazl
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Claesson, Leif
    University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory. University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory.
    Linden, Elisabet
    University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory. University of Gävle, Faculty of Engineering and Sustainable Development, BMG laboratory.
    Khan, Mubashar
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Viewpoints on wind and air infiltration phenomena at buildings illustrated by field and model studies2015In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 92, p. 504-517Article in journal (Refereed)
    Abstract [en]

    Ventilation and infiltration caused by wind are difficult to predict because they are non-local phenomena: driving factors depend on the surrounding terrain and neighbouring buildings and on the building orientation with respect to the wind direction. Wind-driven flow through an opening is complex because wind can flow through the opening or around the building, in contrast to buoyancy driven flow. We explored wind and air infiltration phenomena in terms of pressure distributions on and around buildings, stagnation points, flow along façades, drag forces, and air flow through openings. Field trials were conducted at a 19th-century church, and wind tunnel tests were conducted using a 1:200 scale model of the church and other models with openings.

     

    The locations of stagnation points on the church model were determined using particle image velocimetry measurements. Multiple stagnation points occurred. The forces exerted on the church model by winds in various directions were measured using a load cell. The projected areas affected by winds in various directions were calculated using a CAD model of the church. The area-averaged pressure difference across the church was assessed. A fairly large region of influence on the ground, caused by blockage of the wind, was revealed by testing the scale model in the wind tunnel and recording the static pressure on the ground at many points. The findings of this study are summarized as a number of steps that we suggest to be taken to improve analysis and predictions of wind driven flow in buildings.

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