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  • 1.
    Antoniou, Nestoras
    et al.
    Department of Civil and Environmental Engineering, University of Cyprus, Nicosia, Cyprus; Department of the Built Environment, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Montazeri, Hamid
    Department of the Built Environment, Eindhoven University of Technology, Eindhoven, The Netherlands; Department of Civil Engineering, KU Leuven, Leuven, Belgium.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Neophytou, Marina
    Department of Civil and Environmental Engineering, University of Cyprus, Nicosia, Cyprus.
    Blocken, Bert
    Department of the Built Environment, Eindhoven University of Technology, Eindhoven, The Netherlands; Department of Civil Engineering, KU Leuven, Leuven, Belgium.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    CFD and wind-tunnel analysis of outdoor ventilation in a real compact heterogeneous urban area: evaluation using “air delay”2017Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 126, s. 355-372Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Outdoor urban ventilation in a real complex urban area is investigated by introducing a new ventilation indicator – the "air delay". Computational Fluid Dynamics (CFD) simulations are performed using the 3D steady Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) approaches. The up-to-date literature shows the lack of detailed evaluations of the two approaches for real compact urban areas. This study further presents a systematic evaluation of steady RANS and LES for the assessment of the ventilation conditions in a dense district in Nicosia, Cyprus. The ventilation conditions within the urban area are investigated by calculating the distribution of the age of air. To better assess the outdoor ventilation, a new indicator, the "air delay" is introduced as the difference between the local mean age of air at an urban area and that in an empty domain with the same computational settings, allowing the comparison of the results in different parts of the domain, without impact of the boundary conditions. CFD results are validated using wind-tunnel measurements of mean wind speed and turbulence intensity performed for the same urban area. The results show that LES can accurately predict the mean wind speed and turbulence intensity with the average deviations of about 6% and 14%, respectively, from the wind-tunnel measurements while for the steady RANS, these are 8% and 31%, respectively. The steady RANS simulations overestimate the local mean air delay. The deviation between the two approaches is 52% at pedestrian level (2 m).

  • 2.
    Buccolieri, R.
    et al.
    Dipartimento di Informatica, Università Ca' Foscari Venezia, Mestre-Venezia, Italy; Dipartimento di Scienza Dei Materiali, University of Salento, Lecce, Italy.
    Sartoretto, F.
    Dipartimento di Informatica, Università Ca' Foscari Venezia, Mestre-Venezia, Italy.
    Giacometti, A.
    Dipartimento di Scienza Dei Materiali, University of Salento, Lecce, Italy.
    Di Sabatino, S.
    Dipartimento di Scienza Dei Materiali, University of Salento, Lecce, Italy.
    Leo, L.
    Dipartimento di Scienza Dei Materiali, University of Salento, Lecce, Italy.
    Pulvirenti, B.
    Dipartimento di Ingegneria Energetica, Nucleare e Del Controllo Ambientale, University of Bologna, Bologna, Italy.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Flow and pollutant dispersion within the Canal Grande channel in Venice (Italy) via CFD techniques2010Ingår i: HARMO 2010 - Proceedings of the 13th International Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes / [ed] Albergel, A., 2010, s. 760-764Konferensbidrag (Refereegranskat)
    Abstract [en]

    The present paper is aimed at the analysis of flow and pollutant dispersion in a portion of the Canal Grande (Grand Canal) in Venice (Italy) by means of both Computational Fluid Dynamics (CFD) FLUENT simulations and wind tunnel experiments performed at the University of Gävle (Sweden). For this application, Canal Grande can be viewed as a sort of street canyon where the bottom surface is water and bus boat emissions are the major source of pollution. Numerical investigations were made to assess the effect of the water surface on air flow and pollutant concentrations in the atmosphere. One of the challenges has been to deal with the interface between two immiscible fluids which requires ad-hoc treatment of the wall in terms of the numerical scheme adopted and the grid definition which needs to be much finer than in typical numerical airflow simulations in urban street canyons. Preliminary results have shown that the presence of water at the bottom of the street canyon modifies airflow and turbulence structure with direct consequences on concentration distribution within the domain.

  • 3.
    Buccolieri, R.
    et al.
    Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, University of Salento, Lecce, Italy.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Sabatino, S. D.
    Department of Physics and Astronomy, University of Bologna, Italy.
    On the drag force distribution over arrays of cubical buildings: Wind tunnel experiments2017Ingår i: HARMO 2017 - 18th International Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes, Proceedings, Hungarian Meteorological Service , 2017, s. 384-388Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we discuss the distribution of drag force along aligned arrays of cubes of different packing density. The distribution is evaluated via wind tunnel measurements performed on individual cubes located along the middle column of the array using a balance provided by a standard load cell. Results are compared with the drag force estimated by a pressure-derived method and clearly show a change of the distribution of the drag force. The force is uniform at low packing densities, while mostly acting on first rows of the arrays at large packing densities. This work leaves room for research tailored to a better parameterization of urban effects in dispersion models.

  • 4.
    Buccolieri, Riccardo
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap. Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, University of Salento, Lecce, Italy.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Di Sabatino, Silvana
    Department of Physics and Astronomy, University of Bologna, Bologna, Italy.
    The drag force distribution within regular arrays of cubes and its relation to cross ventilation – Theoretical and experimental analyses2019Ingår i: Journal of Wind Engineering and Industrial Aerodynamics, ISSN 0167-6105, E-ISSN 1872-8197, Vol. 189, s. 91-103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel set of wind tunnel measurements of the drag force and its spatial distribution along aligned arrays of cubes of height H and planar area index λ p (air gap between cubes) equal to 0.028 (5H) to 0.69 (0.2H) is presented and analysed. Two different types of measurements are compared: one type where the drag force is obtained using the standard load cell method, another type where the drag force is estimated by measuring the pressure difference between windward and the leeward façades. Results show that the drag force is nearly uniformly distributed for lower λ p (0.028 and 0.0625), it decreases up to 50% at the second row for λ p = 0.11, and it sharply decreases for larger λ p (from 0.25 to 0.69) where the force mostly acts on the first row. It follows that for the lowest λ p the drag force typically formulated as a drag area corresponds to the total frontal area of the array, whereas for large λ p the drag area corresponds to the area of the first row. By assessing the driving pressure for ventilation from the drag force, the analysis is extended to estimate the cross ventilation as an example of application of this type of measurements. 

  • 5.
    Buccolieri, Riccardo
    et al.
    Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, University of Salento, Lecce, Italy.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Di Sabatino, Silvana
    Department of Physics and Astronomy, University of Bologna, Bologna, Italy.
    Direct measurements of the drag force over aligned arrays of cubes exposed to boundary-layer flows2017Ingår i: Environmental Fluid Mechanics, ISSN 1567-7419, E-ISSN 1573-1510, Vol. 17, nr 2, s. 373-394Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wind tunnel measurements of the total drag force for aligned arrays of cubes exposed to two different boundary-layer flows at three flow velocities are discussed. The drag force for eight different building packing densities λp (from 0.028 to 1) is measured with a standard load cell generating a novel dataset. Different λp are reproduced by increasing the number of buildings on the same lot area; this represents a real situation that an urban planner is faced with when a lot area of a given (fixed) size is allocated to the development of new built areas. It is assumed that the surrounding terrain is uniform and there is a transition from a given roughness (smooth) to a new roughness (rough). The approaching flow will adjust itself over the new surface within a distance that in general may be larger than the horizontal length covered by the array. We investigate the region where the flow adjustment occurs. The wide range of packing densities allowed us to analyse in detail the evolution of the drag force. The drag force increases with increasing packing densities until it reaches a maximum at an intermediate packing density (λp = 0.25 in our case) followed by a slight decrease at larger packing densities. The value of the drag force depends on the flow adjustment along the array which is evaluated by introducing the parameter “drag area” to retrieve information about the drag distribution at different λp. Results clearly suggest a change of the distribution of the drag force, which is found to be relatively uniform at low packing densities, while most of the force acts on first rows of the arrays at large packing densities. The drag area constitutes the basis for the formulation of a new adjustment length scale defined as the ratio between the volume of the air within the array and the drag area. The proposed adjustment length scale automatically takes into account the change in drag distribution along the array for a better parameterization of urban effects in dispersion models. 

  • 6.
    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
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Claesson, Leif
    Högskolan i Gävle, Akademin för teknik och miljö, BMG-labbet.
    Di Sabatino, Silvana
    University of Bologna, Bologna, Italy.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    The impacts of building height variations and building packing densities on flow adjustment and city breathability in idealized urban models2017Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 118, s. 344-361Artikel i tidskrift (Refereegranskat)
    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. 

  • 7. Cooper, Ed
    et al.
    Etheridge, David
    Mattsson, Magnus
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Pressure Pulse Technique – A New Method for Measuring the Leakage of the Building Envelope of Churchesmms2011Konferensbidrag (Refereegranskat)
  • 8.
    Cooper, Ed W
    et al.
    University of Nottingham, UK.
    Etheridge, David W
    University of Nottingham, UK.
    Mattsson, Magnus
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Measurement of the adventitious leakage of churches with a novel pulse technique2011Ingår i: Proc. Roomvent 2011: 12th International conference on air distribution in rooms / [ed] Hans Martin Mathisen, Trondheim, Norge: Tapir Akademisk Forlag , 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    The University of Gavle is currently involved in a project on saving energy in historic buildings (churches). An important factor in the determination of the natural ventilation rate is the adventitious leakage of the envelope. Measurement of leakage is therefore a key feature of the investigations. It was decided to adopt a new technique developed at the University of Nottingham (UNott). It is a pulse technique compared to the conventional steady technique.

    The conventional technique consists of generating a steady and high pressure difference (50 Pa) across the envelope by means of a fan. Such pressures are rarely encountered in ventilation and this leads to errors in the low-pressure leakage. Furthermore the use of the conventional blower door technique in churches is difficult due to their large volume and the need to replace the doors.

    The underlying principle of the UNott technique is described and examples of results are given. The most important advantage of the Unott technique is that the leakage is determined at the low pressure differences that are encountered with ventilation e.g. 4 Pa. This is made possible primarily by the fact that the effects of wind and buoyancy at the time of the test are eliminated by taking account of the pressure variation before and after the pulse.

    For measurements in large buildings, a number of identical piston/cylinder units have to be operated simultaneously. The University of Gävle has developed a system whereby up to seven units can be used. Such a number is required for a leaky church and this is the first time this has been done.

  • 9.
    Iqbal, Ahsan
    et al.
    Danish Building Research Institute, Aalborg University, Copenhagen, Denmark .
    Afshari, Aliresa
    Danish Building Research Institute, Aalborg University, Copenhagen, Denmark .
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Heiselberg, Per
    Indoor Environmental Engineering, Aalborg University, Aalborg, Denmark .
    Discharge coefficient of centre-pivot roof windows2015Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 92, s. 635-643Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Use of centre-pivot roof windows is very common in single family houses in Nordic Europe. Unfortunately the wind-driven airflow characteristics of this kind of windows are missing in the scientific literature. In the present study, the airflow rate through the window was specified by using the discharge coefficient. Wind tunnel measurements using a modelled centre-pivot roof windowwas used in the present study. For smaller sash opening angles the value of discharge coefficientwas approaching unity and the discharge coefficient decreased with increase in the sash opening angle. The value of 0.6 was only obtained when the window was without sash. Hence, the inclusion of sash improved the airflow characteristics of the window due to increased value of the dischargecoefficient. The discharge coefficient also depended on turbulence in the flow. In the absence of external wind, the turbulence was described by the value of Re. Only for higher values of Re the still-air discharge coefficients became independent of the flow direction and the air velocity. Whereas for wind driven natural ventilation the ratio of average air speed within the opening and the reference wind speed (velocity ratio) was used to define the fully developed turbulent flow. Constant values of wind-driven discharge coefficients were obtained when the average air speed within the opening was equal to or greater than the reference wind speed i.e. the velocity ratio greater than unity. Moreover, when the velocity ratio was greater than unity, the still-air discharge coefficients became identical to the wind-driven discharge coefficients.

  • 10.
    Iqbal, Ahsan
    et al.
    Danish Building Research Institute, Aalborg University, Copenhagen, Denmark .
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Heiselberg, Per
    Indoor Environmental Engineering, Aalborg University, Aalborg, Denmark.
    Afshari, Aliresa
    Danish Building Research Institute, Aalborg University, Copenhagen, Denmark .
    Effect of opening the sash of a centre-pivot roof window on wind pressure coefficients2014Ingår i: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 13, nr 3, s. 273-284Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes the effect of outward opening the sash of a window on local and overall windpressures. Wind tunnel experiments were used for the purpose of evaluation. A centre-pivot roofwindow on a pitched roof in a modelled scaled building was used in the analysis of wind pressures.The wind pressures were defined in terms of wind pressure coefficients. Traditionally, wind pressurecoefficients are extracted from the analysis of a sealed plane surface. These wind pressurecoefficients are used to estimate the natural ventilation rate through windows/openings due to windeffect. Surface averaged wind pressure coefficients do not accurately estimate the airflow rates. Therefore, local wind pressure coefficients are needed, especially for dynamic calculation of airflow rates. From the wind tunnel experiments, it is concluded that outward opening the sash can significantly affect the wind pressure distribution near to the window. The use of wind pressurecoefficients from the analysis of a sealed plane surface may lead to erroneous estimation of airflow rate.

  • 11.
    Kabanshi, Alan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Ameen, Arman
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Yang, Bin
    Department of Applied Physics and Electronics, Umeå University, Umeå, Sweden.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Energy simulation and analysis of an intermittent ventilation system under two climates2017Ingår i: 10th International Conference on Sustainable Energy and Environmental Protection: Energy Efficiency / [ed] Krope J., Olabi, A.G., Goričanec D. & Božičnik S., Maribor: University of Maribor Press , 2017, s. 1-10Konferensbidrag (Refereegranskat)
    Abstract [en]

    Energy use on heating, ventilation and air conditioning (HVAC) accounts for about 50% of total energy use in buildings.  Energy efficient HVAC systems that do not compromise the indoor environmental quality and at the same time meet the energy reduction directives/policies are necessary and needed. The study herein, evaluates the energy saving potential of a newly proposed ventilation system in spaces with high occupancy density, called Intermittent Air Jet Strategy (IAJS). The aim of the study was to evaluate through simulations the potential energy savings due to IAJS as compared to a mixing ventilation (MV) system in a classroom located in a ‘hot and humid’ climate (Singapore), and in a ‘hot and dry’ climate (Kuwait). The analysis is based on IDA Indoor Climate Energy simulation software. The results herein demonstrate significant reduction of cooling energy use of up 54.5% for Singapore and up to 32.2% for Kuwait with IAJS as compared to MV. Additionally, supply fan energy savings can also be realized if well implemented.

  • 12.
    Kabanshi, Alan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Keus van de Poll, Marijke
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Ljung, Robert
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi.
    Sörqvist, Patrik
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi. Linnaeus Centre HEAD, Swedish Institute for Disability Research, Linköping University, Sweden.
    The effect of heat stress on writing performance in a classroom2014Ingår i: Indoor Air 2014 - 13th International Conference on Indoor Air Quality and Climate, 2014, s. 183-188Konferensbidrag (Refereegranskat)
    Abstract [en]

    Studies have shown that heat stress impairs performance. This depends on the mental loading capacity of the task performed and the exposure time. This is a study of a common task in schools and offices: writing task. It also analyses the occupants’ perceived thermal comfort. The experiment was done in two heat conditions: 20 and 25 centigrade. The between participant design was used. ScriptLog was used to perform the writing task, while questionnaires and a Sudoku task were paper based tasks. The results show that the predicted mean vote (PMV) between conditions was significant (p<0.02) and participants perceived the 20 º C condition to be draughty. They however preferred a little more air movements in both conditions. Writing performance only showed a significant difference (p = 0.03) on deleted characters but the other variables considered did not show any significant differences but showed a strong tendency that with a long exposure time it would eventually be impaired.  This shows that writing despite being a complex task is not a high mental loading task and is not quickly impaired by heat stress.

  • 13.
    Kabanshi, Alan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Measurement of Entrainment into an Axisymmetric Jet using Temperature as a Tracer: A Pilot Study2018Ingår i: Excellent Indoor Climate and High Performing Ventilation / [ed] Risto Kosonen, Mervi Ahola and Jarkko Narvanne, 2018, s. 397-402Konferensbidrag (Refereegranskat)
    Abstract [en]

    The current extended abstract is a pilot study of an ongoing experimental and theoretical investigation of ambient entrainment of room air into an axisymmetric free jet using temperature as a tracer. The project aims to investigate, by revisiting the concepts and fundamentals of axisymmetric free Jets and entrainment in ventilation applications, particularly focusing on how to optimize performance of low mixing air distribution systems and to test methods of measuring entrainment in such systems. The study aims to explore a scalar field method using temperature as a tracer to estimate entrainment in axisymmetric free Jets. The results obtained show jet characteristics that slightly differ from what is reported in velocity field measurements and other scalar field studies. Thus, a call is made herein for further investigations to understand entrainment and appropriate methods to determine jet characteristics and its mixing effect. Additionally, more studies are needed to verify whether earlier results are representative of entrainment conditions for low mixing ventilation systems whose operation mode depend on near-filed characteristics of jets.

  • 14.
    Kabanshi, Alan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Sattari, Amir
    School of Technology and Business Studies, Dalarna University, Sweden.
    Linden, Elisabet
    Högskolan i Gävle, Akademin för teknik och miljö, BMG-labbet.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Experimental study on contaminant entrainment in air distribution systems with free jets2017Ingår i: Healthy Buildings Europe 2017, ISIAQ , 2017, artikel-id 0040Konferensbidrag (Refereegranskat)
    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.

  • 15.
    Kabanshi, Alan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem. Center for the Built Environment, University of California, Berkeley, Berkeley CA, USA.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Experimental Evaluation of Intermittent Air Jet Ventilation Strategy: Cooling effect and the associated energy saving2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    The potential to reduce building energy demand is high especially on building services like ventilation and air conditioning. This potential lies in identifying ventilation strategies that can provide both the required indoor climate and lower the energy use. One of the strategies is optimizing elevated air movements to enhance human convective and evaporative cooling which, as shown in literature, results in reduced energy use on cooling. This paper evaluates the cooling potential and the resulting energy saving of a novel air supply system called intermittent air jet strategy (IAJS). As shown in this study, IAJS with velocities of 0.4 m/s at the breathing height provides a cooling effect equivalent to reducing the ambient temperature in a mixing ventilation system by up to 1.5 oC to achieve a neutral sensation. This translates to a 13% reduction on the cooling demand. The strategy is also shown to have an energy saving potential of up to 50% on the supply fan. 

  • 16.
    Kabanshi, Alan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem. Center for the Built Environment, University of California, Berkeley, Berkeley CA, USA.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Keus van de Poll, Marijke
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi.
    Ljung, Robert
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi.
    Sörqvist, Patrik
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi.
    The influence of heat, air jet cooling and noise on performance in classrooms2015Ingår i: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 14, nr 3, s. 321-332Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The quality of indoor environments influences satisfaction, health, and work performance of the occupants. Additional understanding of the theoretical and practical value of individual indoor parameters in relation to health and performance aids indoor climate designers to obtain desired outcomes. This also results in expenditure savings and increased revenue: health care and improved productivity. Here, we report two experiments that investigated how heat, cooling strategy and background noise influence performance in a full-scale classroom mockup setting. The results show that heat and background noise are detrimental to logic-based tasks and to writing, whilst cooling manipulations can protect performance. Implications for indoor environment design are discussed.

  • 17.
    Kabanshi, Alan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Ljung, Robert
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi.
    Sorqvist, Patrik
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi. Linnaeus Centre HEAD, Swedish Institute for Disability Research, Linköping University, Sweden.
    Perception of intermittent air velocities in classrooms2014Ingår i: Indoor Air 2014 - 13th International Conference on Indoor Air Quality and Climate, 2014, s. 189-191Konferensbidrag (Refereegranskat)
    Abstract [en]

    Classrooms normally host a large number of people and the heat generated provides a challenge cool. Traditional cooling methods by increased low temperature supply airflow rate or use of heat sinks are expensive and mostly inefficient. The strategy of controlled air movements in the occupied zone may prove cheaper and desirable. This research investigates recirculation of room air to provide intermittent velocity cooling in classrooms. The objective of this experiment was to assess how occupants perceive the recirculated intermittent air velocity conditions in classrooms and when the variations should be introduced in the room for optimal results. This was done with a between participant design, accessing how they perceived indoor air quality (IAQ) and the thermal comfort in two velocity conditions: constant low air velocity condition (< 0.15 m/s) and intermittent air velocity condition (0.4 m/s). As shown here; intermittent air velocity has a positive effect on the perceived thermal comfort (p < 0.04) and perception of air quality: less draughty and improved humid perception. The participants perceived the conditions with intermittent velocity to give comfortable feelings and better air quality.  The variations also showed better performance if they were provided at the start of occupancy as opposed to during or after a temperature build up. This strategy can be used in environments where it is rather uneconomical to provide cooling like spaces hosting a group of people: movie theatres, auditoriums, classrooms and perhaps in restaurants.

  • 18.
    Kabanshi, Alan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Ljung, Robert
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi.
    Sörqvist, Patrik
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi.
    Experimental evaluation of an intermittent air supply system – Part 2: Occupant perception of thermal climate2016Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 108, s. 99-109Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A newly proposed intermittent air jet strategy (IAJS) provides satisfactory indoor climate while promising a substantial energy saving potential, as shown in technical (objective) measurements. The strategy creates non-uniform airflow and non-isothermal conditions critical for sedentary operations at elevated temperatures. The current study explored human perception of thermal environment under an IAJS. Assessment of thermal sensation, thermal comfort, and thermal acceptability were collected based on responses from 36 participants. Participants sat in a classroom setup and performed sedentary work. Their clothing had an insulation of 0.51 clo (T-shirt on upper body). Participants were exposed to homogeneous (v < 0.15 m/s) and nonhomogeneous (0.4 m/s < v < 0.8 m/s) velocity conditions across three temperature conditions: 22.5 °C, 25.5 °C and 28.5 °C. The participants found air speeds to be undesirable at lower temperatures, but reported an improved thermal sensation, comfort and acceptability at higher temperatures. As shown here, IAJS generated neutral operable conditions between 24.8 °C and 27.8 °C, within an air speed range of 0.4 m/s to 0.8 m/s. Additionally, air movements induced thermal alliethesia resulting in improved comfort and acceptance of the thermal climate even at lower air speeds in warm temperature conditions. Hence, the current study supports the energy saving potential with IAJS in view of the human perception of the indoor environment.

  • 19.
    Kabanshi, Alan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Ljung, Robert
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi.
    Sörqvist, Patrik
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Miljöpsykologi.
    Human perception of room temperature and intermittent air jet cooling in a classroom2017Ingår i: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 26, nr 4, s. 528-537Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Environments with high temperatures and under steady conditions are perceived poor. The introduction of airflow variations in such environments improves the perception. However the risk of draught is high and to avoid this, variations in high velocity supply is used. This method is far more energy efficient than cooling the entire space as only the occupants are cooled. This paper discusses two studies on occupant cooling conducted at the University of Gävle.  The experiments were performed in a full scale mockup classroom and a total of 85 students participated. In Study 1, students sat in a classroom for about 60 minutes in one of two heat conditions: 20 and 25 º C. In Study 2, the indoor parameters of 25 º C were maintained but airflow variation in the sitting zone was manipulated. In both studies, the participants performed various tasks and answered questionnaires on their perception of the indoor climate. As shown here, higher room temperature deteriorates human perception of the indoor climate in classrooms, and the use of intermittent air jet cooling improves the perception of indoor climate just like cooling by reducing the room air temperature. This study contributes to further knowledge of how convective cooling can be used as a method of cooling in school environments so as to improve on building energy use. 

  • 20.
    Kabanshi, Alan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem. Center for the Built Environment, University of California, Berkeley, USA.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Experimental evaluation of an intermittent air supply system: Part 1: Thermal comfort and ventilation efficiency2016Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 95, s. 240-250, artikel-id 4263Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spaces with high occupancy density e.g.; classrooms, auditoriums and restaurants, provide challenges to ventilate at a lower energy use due to elevated temperatures. To meet occupants’ thermal comfort requirements traditional systems use a lot of energy. Alternative ventilation strategies that optimize high air movements in the occupied zone allow human activities at elevated temperatures while attaining improve occupants’ perception and acceptance of the indoor climate at a low energy use. This paper presents an experimental evaluation of a novel ventilation strategy for high occupancy spaces that provides fresh air and thermal comfort in the sitting zone through a controlled intermittent air jet system. The strategy uses ceiling mounted high momentum air jet diffusers (AJD) made from ventilation duct fitted with nozzles that generate confluent jets. The jets coalesce into a single two-dimensional jet which is directed downwards in the sitting zone. This paper presents an experimental evaluation/analysis of the proposed system with regard to ventilation efficiency and thermal comfort measurements in a classroom mockup. Results show that the system qualifies to be used as a primary ventilation system and has local air change index > 1 inside the jet, and a ventilation efficiency > 50%. The system also provides better thermal climate than mixing and displacement ventilation at elevated temperatures.

  • 21. Lahtimo, Marjo
    et al.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Modelling of colliding isothermal jets from two ceiling diffusers2011Ingår i: Proc. Roomvent 2011: 12th International conference on air distribution in rooms., 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    The objective of the study was to create a simple CFD (Computational Fluid Dynamics) model of colliding isothermal jets from two identical ceiling diffusers facing each other and to study the influence of the distance between the diffusers on the resulting downward jet. The modelling was done using a commercial CFD (Computational Fluid Dynamics) code. Air flows were visualised with smoke in order to analyse the collision point and flow behaviour after the collision. Velocity measurements were carried out to obtain velocity profiles for the supply air diffusers to be used as initial conditions in the CFD simulations. In addition, measurements were made to determine velocity magnitudes in the collided jets at the occupied zone. Different turbulence models were used in the simulations and compared to the visualised and measured data. As a result a valid CFD model describing the behaviour of the two colliding isothermal jets was created. It was concluded that the CFD models adequately described the phenomena and provided useful data to be used in further studies.

  • 22.
    Sandberg, Mats
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Kabanshi, Alan
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Is building ventilation a process of diluting contaminants or delivering clean air?2019Ingår i: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The purpose of this paper is to discuss the performance of air distribution systems intended for dilution of contaminants (e.g. mixing ventilation) and those intended for delivery of clean air to local regions within rooms (e.g. personalized ventilation). We first start by distinguishing the systems by their visiting frequency behaviour. Then, the performance of the systems with respect to their possibility to influence contaminant concentration in the room or regions within the room is dealt with. Dilution capacity concept for mixing systems is discussed, and delivery capacity concept for systems intended to deliver clean air locally is introduced. Various ways for supply of clean air to regions within the room are presented and their pros and cons are discussed. In delivery capacity systems, the most important single parameter is the entrainment of ambient air into the primary supply flow. Therefore, methods of determining entrainment in these systems need to be defined and the results should be included when describing the performance of the air terminal devices.

  • 23.
    Sandberg, Mats
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Mattsson, Magnus
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Hayati, Abolfazl
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Claesson, Leif
    Högskolan i Gävle, Akademin för teknik och miljö, BMG-labbet.
    Linden, Elisabet
    Högskolan i Gävle, Akademin för teknik och miljö, BMG-labbet.
    Khan, Mubashar
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Viewpoints on wind and air infiltration phenomena at buildings illustrated by field and model studies2015Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 92, s. 504-517Artikel i tidskrift (Refereegranskat)
    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.

  • 24.
    Sandberg, Mats
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Neophytou, Marina
    University of Cyprus.
    Fokaides, Paris
    University of Cyprus.
    Panagiotou, I.
    Ioannou, I.
    University of Cyprus.
    Petrou, M.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Linden, Elisabet
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, BMG Labbet.
    Batchvarova, Ekaterina
    Bulgarian Academy of Science.
    Videnov, P.
    Dimitroff, B.
    Bulgarian Academy of Science.
    Ivanov, A.
    Towards optimization of urban planning and architectural parameters for energy use minimization in Mediterranean cities2011Ingår i: WREC 2011, 2011Konferensbidrag (Refereegranskat)
  • 25.
    Sandberg, Mats
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Claesson, Leif
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, BMG Labbet.
    Cehlin, Mathias
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energiteknik.
    A wind tunnel method for screening the interaction between wind turbines in planned wind farms2011Ingår i: Wrec 2011 Linköping Sweden 2011, 2011Konferensbidrag (Refereegranskat)
  • 26.
    Sandberg, Mats
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Kabanshi, Alan
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Is Building Ventilation a Process of Diluting Contaminants or Delivering Clean Air?2018Ingår i: Excellent Indoor Climate and High Performing Ventilation / [ed] Risto Kosonen, Mervi Ahola and Jarkko Narvanne, 2018, s. 253-258Konferensbidrag (Refereegranskat)
    Abstract [en]

    The purpose of the paper is to discuss the performance of air distribution systems intended for dilution of contaminants and those intended for delivery of clean air to local regions within rooms. At first the systems are distinguished by their visiting frequency behaviour. The performance of the systems with respect to their possibility to influence the concentration due to contaminants is dealt with by the concept dilution capacity for mixing systems and by introduction of the concept delivery capacity for systems intended for delivery of clean air locally. Various ways of realizing systems for supply of clean air to regions within a room are presented and their pros and cons are discussed.  The most important single parameter is the entrainment of ambient air into the primary flow that drives the airflow in the room.   

  • 27.
    Sandberg, Mats
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Wigö, Hans
    Högskolan i Gävle, Institutionen för matematik, natur- och datavetenskap, Ämnesavdelningen för naturvetenskap.
    Mattsson, Magnus
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Generation of dust balls and their aerodynamic properties2008Ingår i: Indoor air 2008: Proceedings of the 11th International Conference on Indoor Air Quality and Climate, 17-22 August, Copenhagen, Denmark, Kgs Lyngby: Technical university of Denmark , 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Dust balls, sometimes called dust bunnies or balls of fluff, are balls with threads of textile fibres and hair as a skeleton on which particles, dead skin and debris are attached.

    In the present study, dust balls were sampled from normal homes by the homeowners. The structure of some of the dust balls was studied in a scanning microscope. The weight of each individual dust ball was quantified. Each sample was placed on a plate of a painted particleboard, representing a floor surface, and was exposed to a velocity field generated by the outflow from a rig for calibration of velocity transducers. The velocity was gradually increased until the dust ball started to move. The majority of the dust balls had a weight less than 20 mg. A particleboard is a fairly rough surface and the velocity required to initiate a movement was beyond what usually is generated by a ventilation system. These levels of velocity can only be generated by opening windows or by people’s movements. The mechanisms by which distant textile fibres are brought together was studied by placing textile threads on the plate of particleboard and following the process by taking pictures with a digital camera. The protruding parts of the surface would sometimes catch the textile fibres.

  • 28.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Effects of intermittent air velocity on thermal and draught perception: A field study in a school environment2013Ingår i: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 12, nr 3, s. 249-255Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Air movement in an indoor space may be experienced in very different ways. For persons feeling cool, air movement tends to be perceived as draught, whilst when feeling warm air movement may provide a desired cooling effect. In the transition zone it therefore seems difficult to use constant air velocity as a tool for cooling without creating draught problems. One possible way to use air movement as a method to improve thermal comfort, without resultant draught problems, could be to use intermittent air velocity instead of constant velocity. This new cooling method was implemented in a high school in Sweden and evaluated during spring (April) and autumn (September). The present paper reports results from two field experiments where subjects were exposed to velocity variations. The analysis shows significant effects of velocity condition on thermal comfort and air quality. In summary, people exposed to velocity variation perceived the air as cooler and fresher compared with those exposed to constant low velocity and very few classified the air movement as draught. A further conclusion is that even the pupils who were exposed to velocity variation wanted slightly more air movement.

  • 29.
    Wigö, Hans
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Effects of intermittent air velocity on thermal and draught perception during transient temperature conditions2008Ingår i: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 7, nr 1, s. 59-66Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Previous research has shown that air movement has a significant influence on humans' thermal comfort. For persons feeling cool, air movement tends to be perceived as draught, whilst when feeling warm air movements may provide a desired cooling effect. In the transition zone it therefore seems difficult to use constant air velocity as a tool for cooling without creating draught problems. Nevertheless, from an energy saving perspective it appears to be far more efficient to use enhanced convective cooling, induced by the air movement, to cool only the occupants instead of the entire building. One possible way to use air movement as a method to improve thermal comfort without resultant draught problems could be to use intermittent air velocity instead of constant velocity. The present paper reports results from three experiments where subjects have been exposed to velocity variations, showing support for the hypothesis that it is possible to cool humans and reduce the percentage of occupants who are dissatisfied with the room temperature, without creating draught problems, through intermittent cooling.

  • 30.
    Wigö, Hans
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Field tests of a new cooling method in a school environment2009Ingår i: Proceedings of  11th International Conference on Air Distribution in Rooms, 2009, s. 974-978Konferensbidrag (Refereegranskat)
  • 31.
    Wigö, Hans
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Innovative cooling method in a school environment2007Ingår i: Proceedings of the 2nd PALENC Conference and 28th AIVC Conference: building low energy cooling and advanced ventilation technologies in the 21st century, 27 - 29 September 2007, Crete Island, Greece, Aten: Heliotopos Conferences , 2007, s. Vol. 2, 1114-1116Konferensbidrag (Refereegranskat)
  • 32.
    Wigö, Hans
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Technique and human perception of intermittent air velocity variation.2005Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

     

    Objectives. The main objective of the present thesis was to evolve a controlled intermittent velocity field and to examine the impact of this type of dynamic indoor climate on human’s psychology and physiology. The prediction was that intermittent velocity variation could provide occupants with the desired cooling without causing draught and that this intermittent change of the indoor climate would influence peoples’ affect and cognitive performance.

    Methods. All experiments were performed in a classroom-like environment where groups of subjects were exposed to a temperature increase and step changes in air velocity. The changes or intermittent variations in air velocity consisted of elevated speed during five minutes, which were repeated three times. To reduce the influence of individual thermal preferences all measures were collected twice and the statistical analyses were based on the change scores in these measures.

    Results. The obtained results showed that, intermittent velocity variation may provide occupants with the desired cooling without causing draught. Subjects exposed to velocity variations were significantly less affected by the temperature rise in the room, compared to the control group. Moreover, the method reduced the expected increase of occupants who perceived the temperature condition as uncomfortable. The findings concerning air movements demonstrate that very few perceived the condition as draughty, after being exposed to the three high velocity pulses.

    The results concerning affect showed a significant effect on high activation, in the temperature range 21 - 24oC when the velocity variations made the subjects rate the temperature as slightly lowered over time, they kept their level of activation. In the higher temperature interval, 25 - 27oC, unactivated unpleasantness increased and activated pleasantness decreased significantly more in subjects in the constant velocity condition than it did for subjects in the velocity variation condition. In sum, all results concerning affect, the significant ones and tendencies point in the same direction. Subjects exposed to velocity variation report changes, over time, indicating higher activation and more positive feelings.

    No differences in cognitive performances were shown between the air velocity conditions. However, a tendency to a significant result (p = 0.10) in an attention task was shown, indicating that subjects in the velocity variation condition increased their speed in a short-term memory search, compared to subjects in the constant velocity condition.

    In the temperature range 21- 24oC, where the perception of the room temperature was measured at 0, 5 and 10 minutes respectively after the last high velocity period, the difference in MTV scores between the two groups, did decrease over time. Ten minutes after the last pulse the difference in MTV scores between the two groups was not significant. This suggests that the high velocity period should be repeated every10 to 15 minutes to keep the expected rise in subjects who judged the thermal conditions as uncomfortable down.

    The skin temperature was not affected neither by the rise in ambient temperature (from 21 to 24oC over 80 minutes) nor the periods (3 x 5 minutes) of high velocity. A consequence of this result is that the human temperature regulation system permitted an increased heat loss during the high velocity pulse, and hence a reduction of the body’s internal stored heat. For uncovered body parts the increase in heat loss was 20 % during the high velocity pulse. Summarised over the whole exposure time the three pulses produced a total energy loss that was only 2 % higher compared to constant low velocity.

  • 33.
    Wigö, Hans
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Knez, Igor
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Psychological impact of air velocity variations in a ventilated room2005Ingår i: Ergonomics, ISSN 0014-0139, E-ISSN 1366-5847, Vol. 48, nr 9, s. 1086-1096Artikel i tidskrift (Refereegranskat)
  • 34.
    Wigö, Hans
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - installationsteknik.
    Lahtimo, Marjo
    Colliding isothermal ceiling jets as a method to generate velocity variations in the occupied zone2011Ingår i: Proc. Roomvent 2011: 12th International conference on air distribution in rooms. Trondheim, Norway., 2011Konferensbidrag (Refereegranskat)
  • 35.
    Wigö, Hans
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Nilsson, Håkan O.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Application of a thermal manikin to evaluate heat loss rates from people caused by variations in air velocity and air temperature2004Ingår i: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 3, nr 3, s. 219-225Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Heat loss monitoring from a thermal manikin was undertaken representing an occupant in a classroom during a lesson period of 80 minutes in which the room temperature was increased from 21 to 24°C for various airflow velocity configurations. A group of subjects was exposed to various conditions of temperature and airflow rate so that the impact of these variations on their surface/skin temperature could be determined. It was found that skin temperature remained stable and close to 34°C for all conditions of exposure. Thus, over the temperature and air velocity range considered, these new findings verified the suitability of using a thermal manikin, set to steady uniform surface temperature, to determine the heat loss characteristics from occupants subjected to intermittent velocity variation. When the manikin was exposed to a high velocity pulse, the heat loss from the whole body increased by 10% while the heat loss from exposed areas (hands and face) increased by 20 % (when compared to no velocity pulse). After the 80 minutes monitoring period, the total energy loss from a manikin exposed to velocity variations was 2% higher than when exposed to constant low velocity.

  • 36.
    Wigö, Hans
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Sandberg, Mats
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Creating velocity variations in a whole room2002Ingår i: Proceedings of the 8th International Conference on Air Distribution in Rooms, 2002, s. 273-276Konferensbidrag (Refereegranskat)
  • 37.
    Wigö, Hans
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Sandberg, Mats
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Draught free intermittent cooling at moderate over temperatures by generating pulses of high velocities.2005Ingår i: Proceedings of 10th International Conference on Indoor Air Quality and Climate, 2005, s. 209-213Konferensbidrag (Refereegranskat)
    Abstract [en]

    Schools in Scandinavia are buildings where there is a need of cooling only for a short period of time. Due to the large number of students the ventilation system often cannot provide the necessary cooling without causing draught. We introduce additional cooling by an internal high velocity system that cool people. This system creates a downward air stream of five minutes duration that blows the rising thermal plume above a person away, thus exposing the student to an enhanced convective cooling. As the heat load was high the occupants were at the same time exposed to a rising room temperature. Assessments have been made where groups of subjects were exposed to velocity variations respectively constant low velocity. The mean thermal votes and air quality were measured during 80 minutes. The results are analysed as differences between the two groups in change over time.

  • 38.
    Wigö, Hans
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Sandberg, Mats
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Velocity variations in ventilated rooms as a method for creating comfort2001Ingår i: Proceedings of 22nd AIVC Conference, 2001, s. 27.1-27.12Konferensbidrag (Refereegranskat)
    Abstract [en]

    The aim is to develop a new method for comfort in settings with high thermal load in buildings that do not require continuous cooling but cooling only during shorter periods. Example of such buildings is schools. The present ventilation and control systems are designed for supply of air at a constant flowrate or to respond to relatively slow variations in load or step changes in load. The slow variations in load are mainly governed by the diurnal cycle and sudden step changes in load are mainly due to people entering or leaving a room. Systems of today are monotonous in the sense that the indoor climate is kept almost constant over long periods. However, there are indications that intermittent variations in velocities can be beneficial to people's perceived comfort. For example when people feel too warm the introduction of a short "breeze" of "high velocity" air may make them feel more comfortable. One example is window airing. The use of (non-turbulent) variations as a stimulus for creating comfort has not as yet been explored systematically or been technically implemented. The idea is to create velocity variations in the head region on people. Both momentum (mixing ventilation) and pure buoyancy driven (displacement system) ventilation are used for creating velocity variations. In addition to using the ventilation system for introducing velocity variations, stirring generated by propellers (ceiling fans) are used. The paper reports on the velocity field obtained in the occupied zone.

  • 39.
    Yang, Bin
    et al.
    Department of Applied Physics and Electronics, Umeå University, Umeå, Sweden.
    Melikov, A.K.
    International Centre for Indoor Environment and Energy, Department of Civil Engineering, Technical University of Denmark, Denmark.
    Kabanshi, Alan
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Zhang, C.
    Department of Civil Engineering, Aalborg University, Aalborg, Denmark.
    Bauman, F. S.
    Center for the Built Environment, University of California, Berkeley, CA, United States.
    Cao, G.
    Department of Energy and Process, Norwegian University of Science and Technology, KolbjørnHejesVei 1B, Trondheim, Norway.
    Awbi, H.
    School of Construction Management and Engineering, University of Reading, United Kingdom.
    Wigö, Hans
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Niu, J.
    School of Architecture, Design and Planning, The University of Sydney, Australia.
    Cheong, K. W. D.
    Department of Building, School of Design and Environment, National University of Singapore, Singapore.
    Tham, K. W.
    Department of Building, School of Design and Environment, National University of Singapore, Singapore.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Nielsen, P. V.
    Department of Civil Engineering, Aalborg University, Aalborg, Denmark.
    Kosonen, R.
    Department of Mechanical Engineering, School of Engineering, Aalto University, Espoo, Finland; College of Urban Construction, Nanjing Tech University, Nanjing, China.
    Yao, R.
    School of Construction Management and Engineering, University of Reading, United Kingdom.
    Kato, S.
    Institute of Industrial Science, The University of Tokyo, Tokyo, Japan.
    Sekhar, S. C.
    Department of Building, School of Design and Environment, National University of Singapore, Singapore.
    Schiavon, Stefano
    Center for the Built Environment, University of California, Berkeley, CA, United States.
    Karimipanah, Taghi
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Li, X.
    Department of Building Science, School of Architecture, Tsinghua University, Beijing, China.
    Lin, Z.
    Division of Building Science and Technology, City University of Hong Kong, Hong Kong, Hong Kong.
    A review of advanced air distribution methods - theory, practice, limitations and solutions2019Ingår i: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 202, artikel-id 109359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ventilation and air distribution methods are important for indoor thermal environments and air quality. Effective distribution of airflow for indoor built environments with the aim of simultaneously offsetting thermal and ventilation loads in an energy efficient manner has been the research focus in the past several decades. Based on airflow characteristics, ventilation methods can be categorized as fully mixed or non-uniform. Non-uniform methods can be further divided into piston, stratified and task zone ventilation. In this paper, the theory, performance, practical applications, limitations and solutions pertaining to ventilation and air distribution methods are critically reviewed. Since many ventilation methods are buoyancy driving that confines their use for heating mode, some methods suitable for heating are discussed. Furthermore, measuring and evaluating methods for ventilation and air distribution are also discussed to give a comprehensive framework of the review.

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