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Visualization of Air Flow, Temperature and Concentration Indoors: Whole-field measuring methods and CFD
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The thermal indoor climate is a complicated combination of a number of physical variables, all of which strongly affect people’s well-being. The indoor climate not only heavily affects people’s health and life quality, but also their productivity and ability to work efficiently.

One of the reasons why so many problems are associated with indoor climate is that it is more or less invisible; it is hard to understand something that cannot be seen. In particular, the near-zone of supply air diffusers in displacement ventilation is very critical. Complaints about drafts are often associated with this type of ventilation system.

The main aim of this research is to improve the knowledge of the whole-field techniques used to measure and visualize air temperatures and pollutant concentrations. These methods are explored with respect to applicability and reliability. Computational Fluid Dynamics (CFD) has been used to predict the velocity and temperature distributions and to improve the current limitations.

Infrared thermography is an excellent technique for visualization of air temperature and airflow pattern, particular in areas with high temperature gradient, such as close to diffusers. It is applicable to both laboratory and field test environments, such as in industries and workplaces. For quantitative measurements the recorded temperatures must be corrected for radiation heat exchange with the environment, a complicated task since knowledge about the local heat transfer coefficients, view factors and surrounding surfaces are needed to be known with good accuracy.

Computed tomography together with optical sensing is a promising tool in order to study the dispersion of airborne pollutants in buildings. However, the design of the optical sensing configuration and the reconstruction algorithm has a major influence on the performance of this whole-field measuring technique. A Bayesian approach seems to be a rational choice for reconstruction of pollutant concentration indoors, since it avoids the high noise sensitivity frequently encountered with many other reconstruction methods. A modified Low Third Derivative (LTD) method has been proposed in this work that performs well particular for concentration distributions containing steep gradients and regions with very low concentrations.

CFD simulation is a powerful tool for visualization of velocities, airflow pattern and temperature distribution in rooms. However, for predictions of the absolute value of the physical variables the CFD model have to be validated against some reference case with high quality experimental data. CFD predictions of air temperatures and velocities close to a complex supply diffuser are very troublesome. The performance of CFD prediction of the airflow close to a complex supply diffuser depends mainly on the accuracy of the diffuser, turbulence and wall treatment modeling.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 90 p.
National Category
Other Environmental Engineering
Identifiers
URN: urn:nbn:se:kth:diva-3934ISBN: 91-7178-342-3 (print)OAI: oai:DiVA.org:kth-3934DiVA: diva2:10080
Public defence
2006-05-17, Hus 33, Sal 202, Högskolan i Gävle, Gävle, 10:25
Opponent
Supervisors
Note
QC 20100831Available from: 2006-05-02 Created: 2006-05-02 Last updated: 2011-04-26Bibliographically approved
List of papers
1. Computed Tomography for Gas Sensing Indoors Using a Modified Low Third Derivative Method: Numerical Study
Open this publication in new window or tab >>Computed Tomography for Gas Sensing Indoors Using a Modified Low Third Derivative Method: Numerical Study
2006 (English)In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844Article in journal (Other academic) Submitted
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-5643 (URN)
Note
QS 20120316Available from: 2006-05-02 Created: 2006-05-02 Last updated: 2017-12-14Bibliographically approved
2. Numerical and Experimental Investigation of Airflows and Temperature Patterns of a Low-Velocity Diffuser
Open this publication in new window or tab >>Numerical and Experimental Investigation of Airflows and Temperature Patterns of a Low-Velocity Diffuser
2002 (English)In: Proceedings of 9th International Conference on Indoor Air Quality and Climate, 2002, 765-770 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this article, four turbulence models are studied to capture the flow and temperature behavior of the air close to a low-velocity diffuser for displacement ventilation. Turbulence is modeled by means of one zero-equation model and three different two-equation models, i.e. the LVEL, the RNG, the Standard k-e, and the Chen-Kim model. They are evaluated for their performance in predicting the air flow patterns and temperature profiles close to the diffuser. The models are validated with measurements performed both with traditional point measuring techniques and a whole-field measurement method. The prediction of the velocity and the temperature by the three two-equation models is generally satisfactory. The predictions from the RNG and the Chen-Kim model were almost the same and slightly different than the standard k-e model. The RNG model and the Standard k-e model are computationally much more stable than the Chen-Kim model.

National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-5640 (URN)
Conference
9th International Conference on Indoor Air Quality and Climate
Note
QC 20100831Available from: 2006-05-02 Created: 2006-05-02 Last updated: 2010-08-31Bibliographically approved
3. Numerical modeling of a complex diffuser in a room with displacement ventilation
Open this publication in new window or tab >>Numerical modeling of a complex diffuser in a room with displacement ventilation
2010 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 45, no 10, 2240-2252 p.Article in journal (Refereed) Published
Abstract [en]

A micro/macro-level approach (MMLA) has been proposed which makes it possible for HVAC engineers to easily study the effect of diffuser characteristics and diffuser placement on thermal comfort and indoor air quality. In this article the MMLA has been used to predict the flow and thermal behavior of the air in the near-zone of a complex low-velocity diffuser. A series of experiment has been carried out to validate the numerical predictions in order to ensure that simulations can be used with confidence to predict indoor airflow. The predictions have been performed by means of steady Reynolds Stress Model (RSM) and the results have good agreement both qualitatively and quantitatively with measurements. However, measurements indicated that the diffusion of the velocity and temperature was to some extent under-predicted by the RSM, which might be related to high instability of the airflow close to the diffuser. This effect might be captured by employing unsteady RSM. The present study also shows the importance of detailed inlet supply modeling in the accuracy of indoor air prediction.

Keyword
Numerical simulation, Inlet supply, Displacement ventilation, Reynolds stress model
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-24292 (URN)10.1016/j.buildenv.2010.04.008 (DOI)000279464900019 ()
Note
QC 20100831Available from: 2010-08-31 Created: 2010-08-31 Last updated: 2017-12-12Bibliographically approved
4. Visualization of Isothermal Low-Reynolds Circular Air Jet Using Computed Tomography
Open this publication in new window or tab >>Visualization of Isothermal Low-Reynolds Circular Air Jet Using Computed Tomography
2005 (English)In: Proceedings of the 6th World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics, 2005Conference paper, Published paper (Refereed)
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-5642 (URN)
Conference
6th World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics
Note
QC 20100831Available from: 2006-05-02 Created: 2006-05-02 Last updated: 2010-09-08Bibliographically approved
5. Visualization and Measuring of Air Temperatures Based on Infrared
Open this publication in new window or tab >>Visualization and Measuring of Air Temperatures Based on Infrared
2000 (English)In: Proceedings of the 7th International Conference on Air Distribution in Rooms, 2000, 339-347 p.Conference paper, Published paper (Refereed)
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-5638 (URN)
Conference
7th International Conference on Air Distribution in Rooms
Note
QC 20100831Available from: 2006-05-02 Created: 2006-05-02 Last updated: 2010-08-31Bibliographically approved
6. Measurements of Air Temperatures Close to a Low-Velocity Diffuser in Displacement Ventilation Using Infrared Camera
Open this publication in new window or tab >>Measurements of Air Temperatures Close to a Low-Velocity Diffuser in Displacement Ventilation Using Infrared Camera
2002 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 34, 687-698 p.Article in journal (Refereed) Published
Abstract [en]

The near zone of supply air diffusers is very critical for the indoor climate. Complaints of draft are often associated with low-velocity diffusers in displacement ventilation because the air is discharged directly into the occupied zone. Today, the knowledge of the near zone of these air supply diffusers is insufficient, causing an increased need for better measuring methods and representation of the occupied zone.

A whole-field measuring technique has been developed by the authors for visualization of air temperatures and airflow patterns over a large cross-section. In this particular whole-field method, air temperatures are measured with an infrared camera and a measuring screen placed in the airflow. The technique is applicable to most laboratory and field test environments. It offers several advantages over traditional techniques; for example, it can record real-time images within large areas and capture transient events.

The purpose of this study was to conduct a parameter and error analysis of the proposed whole-field measuring method applied to a flow from a low-velocity diffuser in displacement ventilation. A model of the energy balance, for a solid measuring screen, was used for analyzing the influence of different parameters on the accuracy of the method. The analysis was performed with respect to the convective heat transfer coefficient, emissivity, screen temperature and surrounding surface temperatures.

Theoretically, the temperature difference between the screen and the ambient air was found to be 0.2–2.4 °C for the specific delimitation in the investigation. However, after applying correction the maximum uncertainty of the predicted air temperature was found to vary between 0.62 and 0.98 °C, due to uncertainties in estimating parameters used in the correction. The maximum uncertainty can be reduced to a great extent by estimating the convective heat transfer coefficient more accurately and using a screen with rather low emissivity.

Keyword
Thermography, Whole-field measurement, Infrared camera, Visualization, Air temperature, Airflow pattern
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-5639 (URN)10.1016/S0378-7788(01)00133-5 (DOI)
Note
QC 20100831Available from: 2006-05-02 Created: 2006-05-02 Last updated: 2017-12-14Bibliographically approved
7. Computed Tomography for Indoor Applications
Open this publication in new window or tab >>Computed Tomography for Indoor Applications
2006 (English)In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 4, no 4, 349-364 p.Article in journal (Refereed) Published
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-5644 (URN)
Note
QC 20100831Available from: 2006-05-02 Created: 2006-05-02 Last updated: 2017-12-14Bibliographically approved

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