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Wigö, Hans
Publications (10 of 36) Show all publications
Sandberg, M., Wigö, H. & Kabanshi, A. (2018). Is Building Ventilation a Process of Diluting Contaminants or Delivering Clean Air?. In: Risto Kosonen, Mervi Ahola and Jarkko Narvanne (Ed.), Excellent Indoor Climate and High Performing Ventilation: . Paper presented at Roomvent and Ventilation 2018, 2-5 June 2018, Aalto University, Espoo, Finland (pp. 253-258).
Open this publication in new window or tab >>Is Building Ventilation a Process of Diluting Contaminants or Delivering Clean Air?
2018 (English)In: Excellent Indoor Climate and High Performing Ventilation / [ed] Risto Kosonen, Mervi Ahola and Jarkko Narvanne, 2018, p. 253-258Conference paper, Published paper (Refereed)
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.   

Keywords
probability to return, visitation frequency, dilution capacity, delivery capacity, entrainment, mixing factor due to entrainment
National Category
Engineering and Technology
Identifiers
urn:nbn:se:hig:diva-26850 (URN)978-952-5236-48-4 (ISBN)
Conference
Roomvent and Ventilation 2018, 2-5 June 2018, Aalto University, Espoo, Finland
Note

Digital, password-protected proceedings

Available from: 2018-06-07 Created: 2018-06-07 Last updated: 2018-06-11Bibliographically approved
Kabanshi, A., Sandberg, M. & Wigö, H. (2018). Measurement of Entrainment into an Axisymmetric Jet using Temperature as a Tracer: A Pilot Study. In: Risto Kosonen, Mervi Ahola and Jarkko Narvanne (Ed.), Excellent Indoor Climate and High Performing Ventilation: . Paper presented at Roomvent and Ventilation 2018, 2-5 June 2018, Aalto University, Espoo,Finland (pp. 397-402).
Open this publication in new window or tab >>Measurement of Entrainment into an Axisymmetric Jet using Temperature as a Tracer: A Pilot Study
2018 (English)In: Excellent Indoor Climate and High Performing Ventilation / [ed] Risto Kosonen, Mervi Ahola and Jarkko Narvanne, 2018, p. 397-402Conference paper, Published paper (Refereed)
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.

Keywords
Entrainment, jets, near-field, passive tracer, temperature, delivery capacity
National Category
Engineering and Technology
Identifiers
urn:nbn:se:hig:diva-26849 (URN)978-952-5236-48-4 (ISBN)
Conference
Roomvent and Ventilation 2018, 2-5 June 2018, Aalto University, Espoo,Finland
Note

Digital, password-protected proceedings

Available from: 2018-06-07 Created: 2018-06-07 Last updated: 2018-06-11Bibliographically approved
Antoniou, N., Montazeri, H., Wigö, H., Neophytou, M., Blocken, B. & Sandberg, M. (2017). CFD and wind-tunnel analysis of outdoor ventilation in a real compact heterogeneous urban area: evaluation using “air delay”. Building and Environment, 126, 355-372
Open this publication in new window or tab >>CFD and wind-tunnel analysis of outdoor ventilation in a real compact heterogeneous urban area: evaluation using “air delay”
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2017 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 126, p. 355-372Article in journal (Refereed) Published
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).

Keywords
Air delay, City breathability, Computational Fluid Dynamics (CFD), Large Eddy Simulations (LES), Steady RANS, Urban microclimate
National Category
Engineering and Technology
Identifiers
urn:nbn:se:hig:diva-25585 (URN)10.1016/j.buildenv.2017.10.013 (DOI)000417010000030 ()2-s2.0-85042085549 (Scopus ID)
Available from: 2017-11-24 Created: 2017-11-24 Last updated: 2018-03-15Bibliographically approved
Buccolieri, R., Wigö, H., Sandberg, M. & Di Sabatino, S. (2017). Direct measurements of the drag force over aligned arrays of cubes exposed to boundary-layer flows. Environmental Fluid Mechanics, 17(2), 373-394
Open this publication in new window or tab >>Direct measurements of the drag force over aligned arrays of cubes exposed to boundary-layer flows
2017 (English)In: Environmental Fluid Mechanics, ISSN 1567-7419, E-ISSN 1573-1510, Vol. 17, no 2, p. 373-394Article in journal (Refereed) Published
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. 

Keywords
Adjustment length scale, Cubic building arrays, Drag area, Drag force, Planar area index, Standard load cell
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:hig:diva-22978 (URN)10.1007/s10652-016-9493-9 (DOI)000410853200009 ()2-s2.0-84996587562 (Scopus ID)
Available from: 2016-12-07 Created: 2016-12-07 Last updated: 2018-03-13Bibliographically approved
Kabanshi, A., Ameen, A., Yang, B., Wigö, H. & Sandberg, M. (2017). Energy simulation and analysis of an intermittent ventilation system under two climates. In: Krope J., Olabi, A.G., Goričanec D. & Božičnik S. (Ed.), 10th International Conference on Sustainable Energy and Environmental Protection: Energy Efficiency. Paper presented at SEEP 2017, 10th International Conference on Sustainable Energy & Environmental Protection, 27-30 June 2017, Bled, Slovenia (pp. 1-10). Maribor: University of Maribor Press
Open this publication in new window or tab >>Energy simulation and analysis of an intermittent ventilation system under two climates
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2017 (English)In: 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, p. 1-10Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
Maribor: University of Maribor Press, 2017
Keywords
Intermittent air jets, Energy simulation; Energy saving, Setpoint extension, Convective cooling
National Category
Energy Systems
Identifiers
urn:nbn:se:hig:diva-24671 (URN)978-961-286-050-9 (ISBN)
Conference
SEEP 2017, 10th International Conference on Sustainable Energy & Environmental Protection, 27-30 June 2017, Bled, Slovenia
Available from: 2017-07-04 Created: 2017-07-04 Last updated: 2019-01-09Bibliographically approved
Kabanshi, A., Sattari, A., Linden, E., Wigö, H. & Sandberg, M. (2017). Experimental study on contaminant entrainment in air distribution systems with free jets. In: Healthy Buildings Europe 2017: . Paper presented at HB2017-Europe, Healthy Buildings Europe 2017, 2-5 July 2017, Lublin, Poland. ISIAQ, Article ID 0040.
Open this publication in new window or tab >>Experimental study on contaminant entrainment in air distribution systems with free jets
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2017 (English)In: Healthy Buildings Europe 2017, ISIAQ , 2017, article id 0040Conference paper, Published 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.

Place, publisher, year, edition, pages
ISIAQ, 2017
Keywords
Ambient entrainment, Jet development, PIV, Reynolds numbers
National Category
Energy Systems
Identifiers
urn:nbn:se:hig:diva-24672 (URN)2-s2.0-85053896607 (Scopus ID)978-83-7947-232-1 (ISBN)
Conference
HB2017-Europe, Healthy Buildings Europe 2017, 2-5 July 2017, Lublin, Poland
Note

Digital conference proceedings distributed to participants on USB.

Available from: 2017-07-04 Created: 2017-07-04 Last updated: 2018-10-15Bibliographically approved
Kabanshi, A., Wigö, H., Ljung, R. & Sörqvist, P. (2017). Human perception of room temperature and intermittent air jet cooling in a classroom. Indoor + Built Environment, 26(4), 528-537
Open this publication in new window or tab >>Human perception of room temperature and intermittent air jet cooling in a classroom
2017 (English)In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 26, no 4, p. 528-537Article in journal (Refereed) Published
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. 

Keywords
Heat, air jet cooling, Air velocity variations, Human perception, Indoor air quality, thermal sensation
National Category
Psychology (excluding Applied Psychology) Building Technologies
Identifiers
urn:nbn:se:hig:diva-20211 (URN)10.1177/1420326X16628931 (DOI)000400158700008 ()2-s2.0-85019000704 (Scopus ID)
Available from: 2015-09-07 Created: 2015-09-07 Last updated: 2018-03-13Bibliographically approved
Buccolieri, R., Wigö, H., Sandberg, M. & Sabatino, S. D. (2017). On the drag force distribution over arrays of cubical buildings: Wind tunnel experiments. In: HARMO 2017 - 18th International Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes, Proceedings: . Paper presented at 18th International Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes, HARMO 2017, 9-12 October 2017, Bologna, Italy (pp. 384-388). Hungarian Meteorological Service
Open this publication in new window or tab >>On the drag force distribution over arrays of cubical buildings: Wind tunnel experiments
2017 (English)In: HARMO 2017 - 18th International Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes, Proceedings, Hungarian Meteorological Service , 2017, p. 384-388Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
Hungarian Meteorological Service, 2017
Keywords
Cubic building arrays., Drag distribution, Standard load cell, Atmospheric movements, Wind tunnels, Aligned arrays, Cubic building, Dispersion models, Packing density, Standard loads, Urban effect, Wind tunnel experiment, Wind tunnel measurements, Drag
National Category
Energy Systems
Identifiers
urn:nbn:se:hig:diva-26793 (URN)2-s2.0-85047201752 (Scopus ID)
Conference
18th International Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes, HARMO 2017, 9-12 October 2017, Bologna, Italy
Available from: 2018-06-05 Created: 2018-06-05 Last updated: 2018-06-05Bibliographically approved
Chen, L., Hang, J., Sandberg, M., Claesson, L., Di Sabatino, S. & Wigö, H. (2017). The impacts of building height variations and building packing densities on flow adjustment and city breathability in idealized urban models. Building and Environment, 118, 344-361
Open this publication in new window or tab >>The impacts of building height variations and building packing densities on flow adjustment and city breathability in idealized urban models
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2017 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 118, p. 344-361Article in journal (Refereed) Published
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. 

Keywords
Building height variation, City breathability, Computational fluid dynamics (CFD) simulation, Exchange velocity, Flow adjustment, Wind tunnel, Buildings, Drag, Fluid dynamics, Velocity, Wind tunnels, Building height variations, Computational fluid dynamics simulations, Computational fluid dynamics
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:hig:diva-24214 (URN)10.1016/j.buildenv.2017.03.042 (DOI)000401374600026 ()2-s2.0-85017542097 (Scopus ID)
Note

Funding agencies:

National Natural Science Foundation of China Grant no: 51478486 and 41622502

National Science Fund for Distinguished Young Scholars Grant no: 41425020 

Fundamental Research Funds for the Central Universities Grant no: 161gzd01

Science and Technology program of Guangzhou, China Grant no:  201607010066 

Available from: 2017-06-14 Created: 2017-06-14 Last updated: 2018-03-13Bibliographically approved
Kabanshi, A., Wigö, H., Ljung, R. & Sörqvist, P. (2016). Experimental evaluation of an intermittent air supply system – Part 2: Occupant perception of thermal climate. Building and Environment, 108, 99-109
Open this publication in new window or tab >>Experimental evaluation of an intermittent air supply system – Part 2: Occupant perception of thermal climate
2016 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 108, p. 99-109Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Intermittent air jets, Convective cooling, Thermal comfort, Thermal acceptability, Thermal preference, Thermal satisfaction
National Category
Energy Engineering
Identifiers
urn:nbn:se:hig:diva-22336 (URN)10.1016/j.buildenv.2016.08.025 (DOI)000385324300009 ()2-s2.0-84984810423 (Scopus ID)
Available from: 2016-08-31 Created: 2016-08-31 Last updated: 2018-03-22Bibliographically approved
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