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Kabanshi, A. & Sandberg, M. (2019). Entrainment and its Implications on Microclimate Ventilation Systems: Scaling the Velocity and Temperature Field of a Round Free Jet. Indoor Air, 29(2), 331-346
Open this publication in new window or tab >>Entrainment and its Implications on Microclimate Ventilation Systems: Scaling the Velocity and Temperature Field of a Round Free Jet
2019 (English)In: Indoor Air, ISSN 0905-6947, E-ISSN 1600-0668, Vol. 29, no 2, p. 331-346Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
Entrainment, Round free jet, Microclimate ventilation systems, Temperature field, Velocity field, Entrainment mixing factor
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:hig:diva-28736 (URN)10.1111/ina.12524 (DOI)2-s2.0-85059514934 ()30500986 (PubMedID)
Available from: 2018-12-02 Created: 2018-12-02 Last updated: 2019-02-27Bibliographically approved
Kabanshi, A., Yang, B., Sörqvist, P. & Sandberg, M. (2019). Occupants’ perception of air movements and air quality in a simulated classroom with an intermittent air supply system. Indoor + Built Environment, 28(1), 63-76
Open this publication in new window or tab >>Occupants’ perception of air movements and air quality in a simulated classroom with an intermittent air supply system
2019 (English)In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 28, no 1, p. 63-76Article in journal (Refereed) Published
Abstract [en]

The study reported herein builds on occupant response to an intermittent air jet strategy (IAJS), which creates periodic airflow and non-isothermal conditions in the occupied zone.  Previous research has highlighted the benefits of IAJS on thermal climate and supports energy saving potential in view of human thermal perception of the indoor environment. In this study, the goal was to explore occupant acceptability of air movements and perceived indoor air quality, and to determine a way of assessing acceptable air movement conditions under IAJS. Thirty-six participants were exposed to twelve conditions: three room air temperatures (nominal: 22.5, 25.5 and 28.5 oC), each with varied air speeds (nominal: <0.15 m/s under mixing ventilation (MV), and 0.4, 0.6 and 0.8 m/s under IAJS) measured at the breathing height (1.1 m). The results show that participants preferred low air movements at lower temperatures and high air movements at higher temperatures. A model to predict percentage satisfied with intermittent air movements was developed, and predicts that about 87% of the occupants within a thermal sensation range of slightly cool (-0.5) to slightly warm (+0.5), in compliance with ASHRAE standard 55, will find intermittent air movements acceptable between 23.7 oC and 29.1 oC within a velocity range of 0.4 – 0.8 m/s.  IAJS also improved participants’ perception of air quality in conditions deemed poor under MV. The findings support the potential of IAJS as a primary ventilation system in high occupant spaces such as classrooms. 

Keywords
Intermittent air jets, Air movement acceptability, Perceived air quality, High occupant density
National Category
Energy Engineering
Identifiers
urn:nbn:se:hig:diva-23753 (URN)10.1177/1420326X17732613 (DOI)000454140000006 ()2-s2.0-85042402784 (Scopus ID)
Available from: 2017-03-15 Created: 2017-03-15 Last updated: 2019-01-28Bibliographically approved
Kabanshi, A., Ameen, A., Hayati, A. & Yang, B. (2018). Cooling energy simulation and analysis of an intermittent ventilation strategy under different climates. Energy, 156, 84-94
Open this publication in new window or tab >>Cooling energy simulation and analysis of an intermittent ventilation strategy under different climates
2018 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 156, p. 84-94Article in journal (Refereed) Published
Abstract [en]

Energy use on heating, ventilation and air conditioning (HVAC) accounts for about 50% of building energy use. To have a sustainable built environment, energy efficient ventilation systems that deliver good indoor environmental quality are needed. This study evaluates the cooling energy saving potential of a newly proposed ventilation system called Intermittent Air Jet Strategy (IAJS) and compares its performance against a mixing ventilation (MV) system in a classroom located in three cities with different climates, Singapore with ‘hot and humid’, Ahvaz with ‘hot and dry’ and Lisbon with “moderate” climate. The results show a significant reduction of cooling energy need and flexibility in control strategies with IAJS as a primary system in hot and humid climates like Singapore. Hot and dry climate with short cool periods like Ahvaz show possible application and considerable energy savings with IAJS as a primary system under optimized variable setpoints, but moderate climates have an increased risk of occupant discomfort likely due to increased draft especially during the cool season.  Thus, IAJS as a secondary system that operates only during cooling season may be conducive for moderate climates like Lisbon. Additionally, the results show that supply fan energy savings can also be realized if well implemented. 

Keywords
Intermittent air jets; IDA-ICE simulation; Energy savings, Convective cooling, Hot and humid climate, Hot and dry climate, Moderate climate
National Category
Energy Engineering
Identifiers
urn:nbn:se:hig:diva-26564 (URN)10.1016/j.energy.2018.05.093 (DOI)000437073600008 ()2-s2.0-85048207413 (Scopus ID)
Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2018-08-15Bibliographically approved
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
Holmgren, M., Kabanshi, A., Marsh, J. E. & Sörqvist, P. (2018). When A+B < A: Cognitive bias in experts' judgment of environmental impact. Frontiers in Psychology, 9, Article ID 823.
Open this publication in new window or tab >>When A+B < A: Cognitive bias in experts' judgment of environmental impact
2018 (English)In: Frontiers in Psychology, ISSN 1664-1078, E-ISSN 1664-1078, Vol. 9, article id 823Article in journal (Refereed) Published
Abstract [en]

When ‘environmentally friendly’ items are added to a set of conventional items, people report that the total set will have a lower environmental impact even though the actual impact increases. One hypothesis is that this “negative footprint illusion” arises because people, who are susceptible to the illusion, lack necessary knowledge of the item’s actual environmental impact, perhaps coupled with a lack of mathematical skills. The study reported here addressed this hypothesis by recruiting participants (‘experts’) from a master’s program in energy systems, who thus have bachelor degrees in energy-related fields including academic training in mathematics. They were asked to estimate the number of trees needed to compensate for the environmental burden of two sets of buildings: One set of 150 buildings with conventional energy ratings and one set including the same 150 buildings but also 50 ‘green’ (energy-efficient) buildings. The experts reported that less trees were needed to compensate for the set with 150 conventional and 50 ‘green’ buildings compared to the set with only the 150 conventional buildings. This negative footprint illusion was as large in magnitude for the experts as it was for a group of novices without academic training in energy-related fields. We conclude that people are not immune to the negative footprint illusion even when they have the knowledge necessary to make accurate judgments.

Keywords
averaging bias, Climate Change, Environmental impact, Judgment, Negative footprint illusion
National Category
Applied Psychology
Identifiers
urn:nbn:se:hig:diva-26530 (URN)10.3389/fpsyg.2018.00823 (DOI)000433393500002 ()29896142 (PubMedID)2-s2.0-85047665372 (Scopus ID)
Available from: 2018-05-02 Created: 2018-05-02 Last updated: 2018-06-25Bibliographically 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. (2017). Experimental study of an intermittent ventilation system in high occupancy spaces. (Doctoral dissertation). Gävle: Gävle University Press
Open this publication in new window or tab >>Experimental study of an intermittent ventilation system in high occupancy spaces
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Spaces with high occupancy density like classrooms are challenging to ventilate and use a lot of energy to maintain comfort. Usually, a compromise is made between low energy use and good Indoor Environmental Quality (IEQ), of which poor IEQ has consequences for occupants’ health, productivity and comfort. Alternative strategies that incorporate elevated air speeds can reduce cooling energy demand and provide occupant’s comfort and productivity at higher operative temperatures. A ventilation strategy, Intermittent Air Jet Strategy (IAJS), which optimizes controlled intermittent airflow and creates non-uniform airflow and non-isothermal conditions, critical for sedentary operations at elevated temperatures, is proposed herein.

The primary aim of the work was to investigate the potential of IAJS as a ventilation system in high occupancy spaces. Ventilation parameters such as air distribution, thermal comfort and indoor air quality are evaluated and the system is compared with a traditional system, specifically, mixing ventilation (MV). A 3-part research process was used: (1) Technical (objective) evaluation of IAJS in-comparison to MV and displacement ventilation (DV) systems. (2) An occupant response study to IAJS. (3) Estimation of the cooling effect under IAJS and its implications on energy use. All studies were conducted in controlled chambers.

The results show that while MV and DV creates steady airflow conditions, IAJS has  cyclic airflow profiles which results in a sinusoidal temperature profile around occupants. Air distribution capability of IAJS is similar to MV, both having a generic local air quality index in the occupied zone. On the other hand, the systems overall air change rate was higher than a MV. Thermal comfort results suggest that IAJS generates comfortable thermal climate at higher operative temperatures compared to MV. Occupant responses to IAJS show an improved thermal sensation, air quality perception and acceptability of indoor environment at higher temperatures as compared to MV. A comparative study to estimate the cooling effect of IAJS shows that upper HVAC setpoint can be increased from 2.3 – 4.5 oC for a neutral thermal sensation compared to a MV. This implies a substantial energy saving potential on the ventilation system. In general, IAJS showed a potential for use as a ventilation system in classrooms while promising energy savings.  

Abstract [sv]

Lokaler där många människor vistas, som t.ex. klassrum, är ofta svåra att ventilera. Att upprätthålla en bra termisk komfort kräver en hög energianvändning. Vanligtvis blir det en kompromiss mellan låg energianvändning och bra kvalitet på inomhusmiljön (IEQ). Dålig IEQ får konsekvenser för människors hälsa, produktivitet och komfort. Alternativa ventilationsstrategier, som använder förhöjda lufthastigheter, kan minska kylbehovet och därmed energianvändningen. I denna avhandling utvärderas en ny ventilationsstrategi, Intermittenta luftstrålar (IAJS), där korta perioder med hög lufthastighet genererar en svalkande effekt, när rummets temperatur upplevs som för hög.

Det primära syftet med arbetet var att undersöka potentialen hos IAJS som ett ventilationssystem för klassrum, där den termiska lasten ofta är hög. Strategin jämförs mot traditionella ventilationsprinciper som omblandande ventilation (MV) och deplacerande ventilation (DV). Parametrar som luftdistributionsindex, termisk komfort, luftkvalitet och energibesparing har utvärderats. Alla studier utfördes i klimatkammare.

Resultaten visar att medan MV och DV skapar konstanta luftflödesförhållanden genererar IAJS cykliska hastighetsprofiler samt en sinusformad temperaturvariation i vistelsezonen. IAJS klarar att bibehålla ett bra termiskt klimat vid högre operativa temperaturer jämfört med MV. I en jämförelse med ett traditionellt HVAC-system visar beräkningar  att dess börvärde kan höjas från 2.3 till 4.5 °C med bibehållen termisk komfort. Detta indikerar en avsevärd energibesparingspotential vid användande av IAJS.

Place, publisher, year, edition, pages
Gävle: Gävle University Press, 2017. p. 74
Series
Studies in the Research Profile Built Environment. Doctoral thesis ; 3
Keywords
Intermittent airflow, Indoor air quality, Perceived air quality, Thermal sensation, thermal comfort, Air movement acceptability, Convective cooling, Cooling effect., Intermittent luftflöde, Luftstrålar, Upplevd luftkvalitet, Termisk komfort, Acceptans av luftrörelser, Konvektiv kylning, Kyleffekt.
National Category
Energy Systems
Identifiers
urn:nbn:se:hig:diva-23754 (URN)978-91-88145-11-6 (ISBN)978-91-88145-12-3 (ISBN)
Public defence
2017-05-18, 12:108, Kungsbäcksvägen 47, Gävle, 10:00 (English)
Opponent
Supervisors
Available from: 2017-04-26 Created: 2017-03-15 Last updated: 2018-03-13Bibliographically 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
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2171-3013

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