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On the performance of stratified ventilation
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem. Linköpings universitet, Energisystem.ORCID-id: 0000-0003-3877-6827
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

People nowadays spend most of their time indoors, for example in their homes, cars, in trains, at work, etc. In Sweden, the energy demand in the built environment is a growing issue. The building sector accounts for 40% of total energy use and 15% of total CO2 emissions, and around one-third of the energy use in the world is related to providing a healthy and good comfort indoors. To achieve acceptable indoor climates new designs for the ventilation systems have been proposed in recent decades, among them stratified ventilation systems.

Stratified ventilation is a concept that often allows good performance for both indoor air quality and thermal comfort. Stratified ventilation systems are effective in reducing cross contamination, since there is virtually no mixing in the space; the temperature and the pollutant concentration increase linearly from the heat source with the height of the occupied zone. There are many different ventilation supply devices using the stratified principle, such as displacement supply device (DSD), impinging jet supply device (IJSD) and wall confluent jet supply device (WCJSD).

The main aim of this thesis is to analyze and compare different supply devices based on stratified ventilation, with different setups, related to thermal indoor climate, energy efficiency and ventilation efficiency. The ultimate goal is to contribute to an increased understanding of how ventilation systems with stratified supply devices perform.

Two scientific methods have mainly been used in this thesis, i.e., experimental and numerical investigations. For numerical experiments the CFD (Computational Fluid Dynamics) code ANSYS and FIDAP have been used. Experimental studies have been performed with thermocouples, Hot-Wire Anemometry (HWA) and Hot-Sphere Anemometry, thermal comfort measurement equipment and tracer gas measurement equipment.

This thesis mainly focuses on three research questions: Interaction between a supply device based on stratified ventilation and downdraft from windows; Flow behavior, energy performance and air change effectiveness for different supply devices based on stratified ventilation; and Thermal comfort for different supply devices based on stratified ventilation.

Research question one showed that the arrangement of displacement supply device and window in cold climate has significant effect on the flow pattern below the window. Different supply airflow rates have an effect on both the velocity and the temperature of the downdraft. In this case the velocity decreased by approximately 9.5% and the temperature in the downdraft decreased 0.5°C when the flowrate from the supply device increased from 10 to 15 l/s.

Research question two showed that airflow patterns between different air supply systems were essentially related to characteristics of air supply devices, such as the type, configuration and position, as well as air supply velocities and momentum. For WCJSD, IJSD and DSD, positions of heat sources (such as occupant, computers, lights and external heat sources) played an important role in formation of the room airflow pattern. One interesting observation is that the temperature in the occupied zone is lower and a more stratified temperature field implies a more efficient heat removal by a stratified air supply device. The results revealed that the lowest temperature in the occupied zone was achieved for DSD, but with IJSD and WCJSD slightly warmer, while the system with a mixing supply device (MSD) showed a much higher temperature. The results confirm that air change effectiveness (ACE) for the DSD, WCJSD and IJSD is close to each other. However, MSD shows lower ACE in all the present papers than IJSD, WCJSD and DSD.

Research question three showed that ventilation systems with stratified supply devices in almost all of the studied cases showed an acceptable level for predicted percentage dissatisfied (PPD), predicted mean vote (PMV) and percentage dissatisfied due to draft (DR). If comparing ventilation systems, using IJSD, WCJSD or DSD with MSD always showed thermal comfort better or at the same level.

Abstract [sv]

Människor spenderar en stor del av sin tid inomhus, exempelvis i sina bostäder och bilar, på tåg och på arbetet. Sveriges energibehov i den byggda miljön har en växande trend. Byggnadssektorn står för 40 % av det totala energibehovet och för 15 % av CO2 utsläppet och för cirka en tredjedel av energianvändningen i världen för att tillhandahålla en hälsosam och bra inomhusmiljö. För att skapa en bra inomhusmiljö har nya sätt att ventilera inomhusmiljön utvecklats under de senaste årtiondena. De olika principer som används för att ventilera en byggnad kan indelas i: kolvströmning, omblandande strömning och deplacerande strömning. De genererar rumsförhållanden som ger olika fördelning av hastighet, temperatur och föroreningar i det ventilerade utrymmet.

Stratifierad ventilation är ett koncept som ofta ger ett bra utfall av både inomhusluftkvalitet och termisk komfort. Stratifierade system är effektiva för att minska korskontaminering, eftersom det nästan inte finns någon omblandning i rummet, temperaturen och föroreningskoncentration ökar linjärt från värmekällan med höjden i vistelsezonen. Det finns många olika ventilationsdon som använder den stratifierade principen, såsom deplacerande ventilationsdon (DSD), impinging jet-ventilationsdon (IJSD) och väggbaserad confluent jet-ventilationsdon (WCJSD).

Huvudsyftet med denna avhandling är att analysera och jämföra olika tilluftsdon baserat på stratifierad princip i olika rumskonfigurationer med avseende på termiskt inomhusklimat, energieffektivitet och ventilationseffektivitet. Det yttersta målet är att bidra till ökad förståelse för hur ventilationssystem med olika stratifierade tilluftsdon fungerar.

Två vetenskapliga metoder har huvudsakligen använts i denna avhandling: experimentella och numeriska analyser. För numeriska analyser har CFD (Computational Fluid Dynamics) använts. De simuleringsprogram som utnyttjats för detta ändamål är ANSYS och FIDAP. Experimenten har utförts med hjälp av termoelement, varmtråds- och varmsfärsteknik, mätutrustning för termisk komfort och mätutrustning för spårgas.

Denna avhandling fokuserar framför allt på tre forskningsfrågor: interaktion mellan ett tilluftsflöde från ett deplacerande don och kallraset från ett fönster; strömningsbilden, energiprestandan och luftbyteseffektiviteten för olika tilluftsdon baserat på stratifierad ventilation; och termisk komfort för olika tilluftsdon baserade på stratifierad ventilation.

Forskningsfråga ett visade att kombinationen av tilluftsflöde genom ett deplacerande don och fönster i kallt klimat har tydlig effekt på strömningsbilden för kallraset under fönstret. Olika tilluftsflöden har en effekt på både hastigheten och temperaturen i kallraset. I detta fall minskade hastigheten med ca 9,5% och temperaturen i kallraset minskade med 0,5°C när flödeshastigheten från tilluftsdonet ökade från 10 till 15 l/s.

Forskningsfråga två visade att luftflödesmönstren mellan olika luftförsörjningssystem väsentligen var relaterade till egenskaper hos tilluftsdonen, såsom typ, konfiguration och position samt lufttillförselhastigheter och impulskraft. För WCJSD, IJSD och DSD spelade värmekällans placering, d.v.s. människor, datorer, belysning och externa värmekällor, en viktig roll vid utformningen av rummets luftflödesmönster. En intressant observation är att temperaturen i vistelsezonen är lägre och rummet har ett mer stratifierat temperaturfält, vilket innebär en effektivare ventilering av den zonen. Resultaten visade att den lägsta temperaturen i vistelsezonen uppnåddes för DSD medan IJSD och WCJSD visade en något högre temperatur, systemet med ett omblandande don (MSD) visade en påtagligt högre temperatur. Resultaten bekräftar också att luftförändringseffektiviteten (ACE) för DSD, WCJSD och IJSD ligger nära varandra. MSD visar dock i alla ingående artiklar lägre ACE än IJSD, WCJSD och DSD.

Forskningsfråga tre visade att ventilationssystem med stratifierade tilluftsdon i nästan samtliga studerade fallen haren acceptabel nivå för predicted mean vote (PPD), predicted mean vote (PMV) och percentage dissatisfied due to draft (DR). Om man jämförde ventilationssystem IJSD, WCJSD eller DSD med MSD visade det sig alltid att den termiska komforten var bättre eller på samma nivå som för MSD.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press , 2018. , s. 87
Nationell ämneskategori
Energiteknik
Identifikatorer
URN: urn:nbn:se:hig:diva-27909DOI: 10.3384/diss.diva-149815ISBN: 9789176852514 (tryckt)OAI: oai:DiVA.org:hig-27909DiVA, id: diva2:1248791
Disputation
2018-09-14, ACAS, A-huset, Campus Valla, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2018-09-17 Skapad: 2018-09-17 Senast uppdaterad: 2019-05-22Bibliografiskt granskad
Delarbeten
1. Thermal analysis of super insulated windows (numerical and experimental investigations)
Öppna denna publikation i ny flik eller fönster >>Thermal analysis of super insulated windows (numerical and experimental investigations)
1999 (Engelska)Ingår i: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 29, nr 2, s. 121-128Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Windows are crucial for people's experience of the indoor climate, especially in the Nordic countries with cold climate and short days during the winter. This paper reports the first results from an ongoing research project focused on an improved integration of windows with the indoor air climate and people's perception of the windows. The thermal performance of a well-insulated window has been investigated both numerically and experimentally in a full scale test room. The window under consideration is a low-emissive triple-glazing window with two closed spaces filled with the inert gas krypton. An oxidised metal with low emissivity factor coats one pane in each space. Experimental and numerical investigations on the thermal performance of the window have been conducted for different winter cases. Temperature data obtained by direct temperature measurement using thermocouples and through numerical analysis are presented. The heat transfer through a window construction depends on three mechanisms i.e., conduction, convection and radiation. In this paper the convection-conducting mechanisms have been closely investigated. The numerical predictions agree well with the results from the measurements.

Nyckelord
Thermal analysis, Low-emissive triple-glazing window, Super insulated windows
Nationell ämneskategori
Energisystem
Identifikatorer
urn:nbn:se:hig:diva-27911 (URN)10.1016/S0378-7788(98)00041-3 (DOI)
Tillgänglig från: 2018-07-26 Skapad: 2018-09-17 Senast uppdaterad: 2019-05-22Bibliografiskt granskad
2. Experimental investigation of downdraught from well-insulated windows
Öppna denna publikation i ny flik eller fönster >>Experimental investigation of downdraught from well-insulated windows
2002 (Engelska)Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 37, nr 11, s. 1073-1082Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Since the climate in the Nordic countries is cold for several months a year, windows are crucial in building envelopes. The current trend to reduce heat losses by building components has resulted in many modifications to window design in order to improve thermal performance and the indoor climate. Improvements in window construction have resulted in a higher surface temperature on the inner pane and considerably lower downdraught, which in turn has created an opportunity for the unconventional design of the heating and ventilation systems. The impetus for this paper is to experimentally investigate the effect of thermal performance, window bay and displacement ventilation on the downdraught. The measurements show that the use of well-insulated windows, besides lowering energy consumption, gives rise to a higher quality of indoor climate. The results show a considerably reduced velocity and turbulent intensity by employing a well-insulated window instead of a conventional one. The influence of the window bay on the downdraught is also shown in the paper. © 2002 Elsevier Science Ltd. All rights reserved.

Nyckelord
Displacement ventilation, Downdraught, Indoor climate, Measurement, Well-insulated window
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:hig:diva-27912 (URN)10.1016/S0360-1323(01)00110-X (DOI)
Tillgänglig från: 2009-10-11 Skapad: 2018-09-17 Senast uppdaterad: 2019-05-22Bibliografiskt granskad
3. Numerical investigation of ventilation performance of different air supply devices in an office environment
Öppna denna publikation i ny flik eller fönster >>Numerical investigation of ventilation performance of different air supply devices in an office environment
2015 (Engelska)Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 90, s. 37-50Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The aim of this study was to compare ventilation performance of four different air supply devices in an office environment with respect to thermal comfort, ventilation efficiency and energy-saving potential, by performing numerical simulations. The devices have the acronyms: Mixing supply device (MSD), Wall confluent jets supply device (WCJSD), Impinging jet supply device (IJSD) and Displacement supply device (DSD). Comparisons were made under identical set-up conditions, as well as at the same occupied zone temperature of about 24.2°C achieved by adding different heat loads and using different air-flow rates. Energy-saving potential was addressed based on the air-flow rate and the related fan power required for obtaining a similar occupied zone temperature for each device. Results showed that the WCJSD and IJSD could provide an acceptable thermal environment while removing excess heat more efficiently than the MSD, as it combined the positive effects of both mixing and stratification principles. This benefit also meant that this devices required less fan power than the MSD for obtaining equivalent occupant zone temperature. The DSD showed a superior performance on heat removal, air exchange efficiency and energy saving to all other devices, but it had difficulties in providing acceptable vertical temperature gradient between the ankle and neck levels for a standing person. 

Nyckelord
Air supply devices, Energy-saving potential, Thermal comfort, Ventilation performance, Air, Energy efficiency, Flow rate, Mixing, Ventilation, Air exchange efficiencies, Air supply, Energy saving potential, Numerical investigations, Thermal environment, Ventilation efficiency, Vertical temperature gradients, Energy conservation, building, computer simulation, indoor air, numerical method, performance assessment
Nationell ämneskategori
Maskinteknik Husbyggnad
Identifikatorer
urn:nbn:se:hig:diva-19292 (URN)10.1016/j.buildenv.2015.03.021 (DOI)000356189000004 ()2-s2.0-84926464708 (Scopus ID)
Forskningsfinansiär
Forskningsrådet Formas, 242-2008-835KK-stiftelsen, 2007/0289
Tillgänglig från: 2015-05-05 Skapad: 2015-05-05 Senast uppdaterad: 2019-05-22Bibliografiskt granskad
4. An experimental investigation of the flow and comfort parameters for under-floor, confluent jets and mixing ventilation systems in an open-plan office
Öppna denna publikation i ny flik eller fönster >>An experimental investigation of the flow and comfort parameters for under-floor, confluent jets and mixing ventilation systems in an open-plan office
Visa övriga...
2015 (Engelska)Ingår i: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 92, s. 48-60Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

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

Nyckelord
Open office, Mixing ventilation (MV), Underfloor air distribution (UFAD), Confluent jets ventilation (CJV)
Nationell ämneskategori
Husbyggnad
Identifikatorer
urn:nbn:se:hig:diva-19327 (URN)10.1016/j.buildenv.2015.04.019 (DOI)000358807800006 ()2-s2.0-84929492281 (Scopus ID)
Forskningsfinansiär
VINNOVA
Tillgänglig från: 2015-05-16 Skapad: 2015-05-16 Senast uppdaterad: 2019-05-22Bibliografiskt granskad
5. Comparison of ventilation performance of three different air supply devices: a measurement study
Öppna denna publikation i ny flik eller fönster >>Comparison of ventilation performance of three different air supply devices: a measurement study
2017 (Engelska)Ingår i: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 16, nr 3, s. 244-254Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

People today spend a significant part of their time in an indoor environment, whether it be home, school, vehicle or workplace. This has put greater demands on indoor environment, in terms of both air quality and thermal comfort. The main objective of building ventilation is to take care of pollutants and lower their concentration, but it is also used to cool or heat indoor air. The aim of this paper was to study the behavior of three different ventilation supply devices, i.e. mixing supply device, displacement supply device and confluent jet supply device, in an office room. Different cases have been studied experimentally with different airflow rates, supply air temperature and supply devices. The results shows that mostly that we can expect, but the results show a very small difference in ventilation efficiency between the different systems and in theory there should be a larger difference. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

Ort, förlag, år, upplaga, sidor
Taylor and Francis Ltd., 2017
Nyckelord
air exchange efficiency, confluent jet ventilation, displacement ventilation, measurement, Mixing ventilation, Air quality, Efficiency, Indoor air pollution, Measurements, Mixing, Ventilation, Air exchange efficiencies, Building ventilations, Jet ventilations, Supply air temperature, Ventilation efficiency, Ventilation performance, Fighter aircraft
Nationell ämneskategori
Energisystem
Identifikatorer
urn:nbn:se:hig:diva-24325 (URN)10.1080/14733315.2017.1299519 (DOI)000406118900008 ()2-s2.0-85016093683 (Scopus ID)
Tillgänglig från: 2017-06-16 Skapad: 2017-06-16 Senast uppdaterad: 2019-05-22Bibliografiskt granskad
6. Numerical investigation of Air Change Effectiveness in an Office Room with Impinging Jet Ventilation
Öppna denna publikation i ny flik eller fönster >>Numerical investigation of Air Change Effectiveness in an Office Room with Impinging Jet Ventilation
2018 (Engelska)Ingår i: Proceedings of the 4th international Conference on Building Energy & Environment / [ed] K. Inthavong*, C.P Cheung, G. Yeoh, J.Y. Tu, Melbourne: Conference On Building Energy & Environment - COBEE2018, Melbourne Australia , 2018, s. 641-646Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Providing occupant comfort and health with minimum use of energy is the ultimate purpose of heating, ventilating and air conditioning systems. This paper presents the air-change effectiveness (ACE) within a typical office room using impinging jet ventilation (IJV ) in combination with chilled ceiling (CC) under different heat loads ranging from 6.5 - 51 W per square meter floor area. In this study, a validated CFD model based on the v2f turbulence model is used for the prediction of air flow pattern and ACE. The interaction effect of chilled ceiling and heat sources results in a complex flow with air circulation. The thermal plumes and air circulation in the room result in a variation of ACE within the room but also close to the occupant. For all studied cases, ACE is above 1.2 close to the occupants, indicating that IJV is more energy efficient than mixing ventilation.

Ort, förlag, år, upplaga, sidor
Melbourne: Conference On Building Energy & Environment - COBEE2018, Melbourne Australia, 2018
Nyckelord
Impinging jet ventilation
Nationell ämneskategori
Energiteknik
Identifikatorer
urn:nbn:se:hig:diva-26567 (URN)978-0-646-98213-7 (ISBN)
Konferens
COBEE2018, 4th international Conference on Building Energy & Environment,5-9 February 2018, Melbourne, Australia
Tillgänglig från: 2018-05-15 Skapad: 2018-05-15 Senast uppdaterad: 2019-05-22Bibliografiskt granskad
7. Comparison of the thermal comfort and ventilation effectiveness in an office room with three different ventilation supply devices: a measurement study
Öppna denna publikation i ny flik eller fönster >>Comparison of the thermal comfort and ventilation effectiveness in an office room with three different ventilation supply devices: a measurement study
2018 (Engelska)Ingår i: Proceedings of14th International Conference of Roomvent & Ventilation, Aalto University , 2018, s. 187-192Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

People spend a significant part of their time in an indoor environment, whether at home, school or workplace. The aim of this paper is to experimentally study the ventilation effectiveness (mean age of air, MAA) and thermal comfort (PMV and PPD) of three different ventilation supply devices, i.e., mixing supply device (MSD), displacement supply device (DSD) and wall confluent jet supply device (WCJSD) in an office room.

This paper is based on analysis from full-scale measurements performed in a laboratory at University of Gävle. The size of the room corresponds to a typical office module for one person. The test room has dimensions of 4.2 x 3.0 x 2.4 m with a volume of 31.24 m3, with the size of the room corresponding to a typical office. Different heat sources are used to simulate the office environment, which corresponds to 31.75 W/m2.

The PMV and PPD are comparable to MSD, WCJSD and DSD as it turns out that MSD has poorer comfort than DSD and WCJSD. DSD and WCJSD have more or less the same thermal comfort performance. When comparing the local mean age of air (MAA) for the studied supply devices, the air is significantly much younger for the DSD and WCJSD than for MSD.  

Ort, förlag, år, upplaga, sidor
Aalto University, 2018
Nyckelord
Mixing ventilation, Displacement ventilation, Wall confluent jet ventilation, Thermal comfort, Ventilation effectiveness
Nationell ämneskategori
Energisystem
Identifikatorer
urn:nbn:se:hig:diva-27913 (URN)9789525236484 (ISBN)
Konferens
Roomvent & Ventilation 2018, Aalto University, Espoo, Finland, June 2-5 2018
Tillgänglig från: 2018-07-26 Skapad: 2018-09-17 Senast uppdaterad: 2019-05-22Bibliografiskt granskad

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