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Air diffusion and solid contaminant behaviour in room ventilation: a CFD based integrated approach
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

One of the most fundamental human needs is fresh air. It has been estimated that people spend comparatively much time in indoor premises. That creates an elevated need for high-quality ventilation systems in buildings. The ventilation airflow rate is recognised as the main parameter for measuring the indoor air quality. It has been shown that the ventilation airflow rates have effects on respiratory diseases, on “sick building syndrome” symptoms, on productivity and perceived air quality. Ventilation is necessary to remove indoor-generated pollutants by diluting these to an acceptable level. The choice of ventilation airflow rate is often based on norms or standards in which the airflow rate is determined based on epidemiological research and field or laboratory measurements. However, the determination of ventilation flow rate is far more complex. Indoor air quality in the occupied zone can be dependent of many factors such as outdoor air quality, airflow rate, indoor generation of pollutants, moisture content, thermal environment and how the air is supplied into the human occupied zone. One needs to acknowledge the importance of air distribution which clearly affects the comfort of occupants. To design a ventilation system which considers all aspects of room ventilation can only be achieved by computer modelling. The objective of this thesis is to investigate air diffusion, indoor air quality and comfort issues by CFD (computational fluid dynamics) modelling. The crucial part of the CFD modelling is to adopt BCs (boundary conditions) for a successful and accurate modelling procedure. Assessing the CFD simulations by validated BCs enabled constructing the ventilation system virtually and various system layouts were tested to meet given design criteria. In parallel, full-scale measurements were conducted to validate the diffuser models and the implemented simplified particle-settling model. Both the simulations and the measurements reveal the full complexity of air diffusion coupled with solid contaminants. The air supply method is an important factor for distribution of heat, air velocity and solid contaminants. The influence of air supply diffuser location, contaminant source location and air supply method was tested both numerically and by measurements to investigate the influence of different parameters on the efficiency of room ventilation. As example of this, the well-known displacement ventilation is not fully able to evacuate large 10 μm airborne particles from a room. Ventilation should control the conditions in the human breathing zone and therefore the ventilation efficiency is an important parameter. A properly designed ventilation system could use less fresh air to maintain an acceptable level of contaminant concentration in the human breathing zone. That is why complete mixing of air is not recommended as the ventilation efficiency is low and the necessary airflow rate is relatively high compared to other ventilation strategies. Especially buoyancy-driven airflows from heat sources are an important part of ventilation and should not be hampered by supply airflow from the diffusers. All the results revealed that CFD presently is the only reliable method for optimising a ventilation system considering the air diffusion and contaminant level in all locations of any kind of room. The last part of the thesis addresses the possibility to integrate the CFD modelling into a building design process where architectural space geometry, thermal simulations and diffuser BCs could be embedded into a normal building design project.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , 95 p.
Series
Trita-KRV, ISSN 1100-7990 ; 2005:03
Keyword [en]
Technology, CFD modelling, airflow rate, ventilation efficiency, diffusers, solid contaminants, IAQ
Keyword [sv]
TEKNIKVETENSKAP
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-270ISBN: 91-7178-037-8 (print)OAI: oai:DiVA.org:kth-270DiVA: diva2:8403
Public defence
2005-06-16, sal 2105, KTH Syd, Campus Haninge, Haninge, 14:00
Opponent
Supervisors
Note
QC 20101007Available from: 2005-06-07 Created: 2005-06-07 Last updated: 2010-10-07Bibliographically approved
List of papers
1. Particle Filtration in a Ventilated Room
Open this publication in new window or tab >>Particle Filtration in a Ventilated Room
2002 (English)In: Indoor Air 2002: 9th International Conference on Indoor Air Quality and Climate / [ed] Levin, H., 2002, 1070-1075 p.Conference paper, Published paper (Refereed)
Abstract [en]

Several studies based on analytical models and numerical simulations have shown that it is difficult to control airborne particle movements in a ventilated room. However, more knowledge and information on particle characteristics and particle movements, in combination with new numerical simulation tools, have recently made it easier to estimate particle patterns. In the present paper new information is used to evaluate the role of filtration and ventilation in the particle elimination process. Key parameters found include the particle aerodynamic diameter and the particle settling velocity governed by Stokes formula. Particle dispersion and settling are highly dependent on the ventilation airflow structure. Calculations with CFD (Computational Fluid Dynamics) show characteristic patterns of particle movements in rooms with displacement ventilation.

Keyword
Filtration, CFD, Simulations, Displacement ventilation, Breathing zone
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5311 (URN)
Note
QC 20101007Available from: 2005-06-07 Created: 2005-06-07 Last updated: 2010-10-07Bibliographically approved
2. Flow behaviour in a ventilated room: measurements and simulations
Open this publication in new window or tab >>Flow behaviour in a ventilated room: measurements and simulations
2002 (English)In: Proceedings of Roomvent 2002: the 8th International Conference on Air Distribution in Rooms, 2002, 197-200 p.Conference paper, Published paper (Refereed)
Keyword
CFD, particles, particle concentrations, numerical simulations
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5312 (URN)
Note
QC 20101007Available from: 2005-06-07 Created: 2005-06-07 Last updated: 2010-10-07Bibliographically approved
3. Characteristics of Particles and their Behaviour in Ventilation Air
Open this publication in new window or tab >>Characteristics of Particles and their Behaviour in Ventilation Air
2003 (English)In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 2, no 1, 45-54 p.Article in journal (Refereed) Published
Abstract [en]

The behaviour of particles in air flow is important for identifying those in various locations in ventilated space. The main reason for this study is to propose a new modelling concept to determine a realistic distribution of particles of different sizes in a space. The goal for this investigation is to divide particles into groups according to their behaviour in air and to improve the existing settling model. The growth of particle aerodynamic diameter in higher relative humidity is also presented. Here, growth of diameter and coagulation is used to determine the control volume concentration. The finite volume method is used to describe the particle concentration in the computational domain. A background to particle properties and theory for calculations are given for this purpose. Results from the literature survey reveal that modelling needs a more systematic approach to cover all sizes of particles with clear classification by behaviour.

Keyword
particle behaviour, particle size, numerical modelling, occupied zone, air flow, control volume, review
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5313 (URN)
Note
QC 20101007Available from: 2005-06-07 Created: 2005-06-07 Last updated: 2017-12-04Bibliographically approved
4. Particle Removal Efficiency in a Numerical Test Room
Open this publication in new window or tab >>Particle Removal Efficiency in a Numerical Test Room
2003 (English)In: PROCEEDINGS OF THE 4TH INTERNATIONAL SYMPOSIUM ON HEATING, VENTILATING AND AIR CONDITIONING, VOLS 1 AND 2, 2003, 191-197 p.Conference paper, Published paper (Refereed)
Abstract [en]

Particle removal efficiency in a ventilated room is investigated. This paper reports the differences in particle removal efficiency with various locations of supply and exhaust devices. Numerical simulations are carried out in a simple test room to illustrate the particle concentrations with different configurations of room ventilation. Several particle sizes are used and the influence of different flow patterns and air change rates are investigated. Particles are supplied to the room with the incoming air. Isothermal conditions with varying air supply velocities are used. Preliminary results indicate that particle removal efficiency is not predominantly influenced by air exchange rate, also the location of the supply/exhaust device is underestimated as an indicator of ventilation effectiveness.

Keyword
ventilation efficiency, numerical simulation, particle, simulation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5314 (URN)000189002100024 ()7-302-07326-0 (ISBN)
Conference
4th International Symposium on Heating, Ventilating and Air Conditioning
Note
QC 20101007Available from: 2005-06-07 Created: 2005-06-07 Last updated: 2010-10-07Bibliographically approved
5. CFD modelling of an industrial air diffuser: predicting velocity and temperature in the near zone
Open this publication in new window or tab >>CFD modelling of an industrial air diffuser: predicting velocity and temperature in the near zone
Show others...
2005 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 40, no 5, 601-615 p.Article in journal (Refereed) Published
Abstract [en]

This article describes experimental and modelling results from CFD simulation of an air diffuser for industrial spaces. The main objective of this paper is to validate a manufacturer model of the diffuser. In the air diffuser, the low velocity part is placed on top of a multi-cone diffuser in order to increase airflow rates and maximize the cooling capacity of a single diffuser unit. This kind of configuration should ensure appropriate performance of industrial air diffusers, which is discussed briefly at the end of the article. The paper illustrates the importance of a simulation model jointly with the manufacturer's product model and the grid layout near the ventilation device to achieve accurate results. Parameters for diffuser modelling were adapted from literature and manufacturer's product data. Correct specification of diffuser geometry and numerical boundary conditions for CFD simulations are critical for prediction. The standard k-epsilon model was chosen to model turbulence because it represents the best-known model utilized and validated for air diffuser performance. CFD simulations were compared systematically with data from laboratory measurements; air velocity was measured by ultrasonic sensors. Results show that CFD simulation with a standard k-epsilon model accurately predicts non-isothermal airflow around the diffuser. Additionally, smoke tests revealed that the flow around the diffuser is not completely symmetrical as predicted by CFD. The cause of the observed asymmetry was not identified. This was the main reason why some simulation results deviate from the measured values.

Keyword
industrial air diffuser, CFD, boundary conditions, velocity distribution, temperature distribution, room, validation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-14557 (URN)10.1016/j.buildenv.2004.08.020 (DOI)000227250900002 ()2-s2.0-13444306430 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
6. CFD Simulation and Measurements in Near Zone of High Induction Swirl Diffuser
Open this publication in new window or tab >>CFD Simulation and Measurements in Near Zone of High Induction Swirl Diffuser
2004 (English)In: Roomvent 2004: Proceedings of the 9th International Conference on Air Distribution in Rooms, 2004Conference paper, Published paper (Refereed)
Keyword
diffuser, measurements, boundary conditions
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-5316 (URN)
Conference
Roomvent 2004, The 9th International Conference on Air Distribution in Rooms, Coimbra, Portugal 5 - 8 Sept., 2004
Note
QC 20101007, QC 20120305Available from: 2005-06-07 Created: 2005-06-07 Last updated: 2012-03-05Bibliographically approved
7. The Influence of Airflow Profile and Heat Source Location on Heat Removal Efficiency
Open this publication in new window or tab >>The Influence of Airflow Profile and Heat Source Location on Heat Removal Efficiency
(English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178Article in journal (Other academic) Submitted
Keyword
CFD simulation, excess heat, heat removal efficiency, air diffuser, heat plume, designed target temperature
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5317 (URN)
Note
QS 20120326Available from: 2005-06-07 Created: 2005-06-07 Last updated: 2017-12-04Bibliographically approved
8. Multi-Zone Model Approach for Evaluating Particle Mass Transport in a Ventilated Room
Open this publication in new window or tab >>Multi-Zone Model Approach for Evaluating Particle Mass Transport in a Ventilated Room
2004 (English)In: RoomVent 2004: 9th International Conference on Air Distribution in Rooms, 2004Conference paper, Published paper (Refereed)
Keyword
particle, zone, behaviour
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5318 (URN)
Note
QC 20101007Available from: 2005-06-07 Created: 2005-06-07 Last updated: 2010-10-07Bibliographically approved
9. CFD Modelling as a Part of Integrated Design Process for Optimised Indoor Environment
Open this publication in new window or tab >>CFD Modelling as a Part of Integrated Design Process for Optimised Indoor Environment
(English)In: Automation in Construction, ISSN 0926-5805, E-ISSN 1872-7891Article in journal (Other academic) Submitted
Keyword
CFD simulation, IFC, integration, product model, design process
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5319 (URN)
Note
QS 20120326Available from: 2005-06-07 Created: 2005-06-07 Last updated: 2017-12-04Bibliographically approved

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Citation style
  • apa
  • harvard1
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  • modern-language-association-8th-edition
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  • Other locale
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