Section 4 - Indoor Airflow and Pollutant Transport

(Clicking on the Report number downloads a PDF file of that report)

Report number: LBNL-748E Year: 2008

Title: Synthesis of Hectorite-TiO2 and Kaolinite-TiO2 Nanocomposites with Photocatalytic Activity for the Degradation of Model Air Pollutants Published in: Submitted to Applied Clay Science.

Authors: Kibanova, D., Trejo, M., Destaillats, H., Cervini-Silva, J. Type: Journal Article

Report number: LBNL-62082 Year: 2008

Title: Indoor pollutants emitted by office equipment: A review of reported data and information needs Published in: Atmospheric Environment, Volume 42, Pages 1371-1388.

Authors: Destaillats, H., Maddalena, R.L., Singer, B.C., Hodgson, A.T., McKone, T.E. Type: Journal Article

Report number: Year: 2007

Title: Influence of indoor transport and mixing times scales on the performance of sensor systems for characterizing contaminant releases Published in: Atmospheric Environment, Volume 41, Pages 9530-9542.

Authors: Sreedharan, P., Sohn, M.D., Nazaroff, W.W., Gadgil, A.J. Type: Journal Article

Report number: Year: 2007

Title: Effect of room air recirculation delay on the decay rate of tracer gas concentration, Published in: Submitted to Indoor Air.

Authors: Lorenzetti, D.M., Kristoffersen, A.H., Gadgil, A.J. Type: Journal Article

Report number: LBNL-62736 Year: 2007

Title: Filter loading corrections for real-time aethalometer measurements of fresh diesel soot. (2007) Published in: Journal of Air and Waste Management Association, Volume 57, Pages 868–873.

Authors: Jimenez, J., Claiborn, C., Larson, T., Kirschtetter, T., Gundel, L.A. Type: Journal Article

Report number: Year: 2007

Title: Rapid Data Assimilation in the Indoor Environment: Theory and Examples from Real-time Interpretation of Indoor Plumes of Airborne Chemical Published in: Pollution Modeling and its Applications XIX in press (2007)..

Authors: Gadgil, A.J., Sohn, M.D., Sreedharan, P., Borrego, C., Miranda, A.I. Type: Book Section

Report number: LBNL-62107 Year: 2007

Title: Effectiveness of urban shelter-in-place. II: Residential Districts Published in: Atmospheric Environment, Volume 41, Pages 7082-7095.

Authors: Chan, W.R., Nazaroff, W.W., Price, P.N., Gadgil, A.J. Type: Journal Article

Report number: LBNL-61686 Year: 2007

Title: Effectiveness of Urban Shelter-in-Place I: Idealized Conditions Published in: Atmospheric Environment, Volume 41, Pages 4962-4976 .

Authors: Chan, W.R., Nazaroff, W.W., Price, P. N., Gadgil, A.J. Type: Journal Article

Report number: Year: 2006

Title: An Attic-Interior Infiltration and Interzone Transport Model of a House Published in: Building and Environment, Volume 40, Pages 701-718.

Authors: Walker, I.S., Forest, T.W., Wilson, D.J. Type: Journal Article

Report number: LBNL-57385 Year: 2006

Title: CFD Investigation of Room Ventilation for Improved Operation of a Downdraft Table: Novel Concepts Published in: Journal of Occupational and Environmental Hygiene, Volume 3, Pages 583-591.

Authors: Jayaraman, B., Kristoffersen, A.H., Finlayson, E.U., Gadgil, A.J. Type: Journal Article

Abstract: We report a computational fluid dynamics (CFD) study of containment of airborne hazardous materials in a ventilated room containing a downdraft table. Specifically, we investigate the containment of hazardous airborne material obtainable under a range of ventilation configurations. The desirable ventilation configuration should ensure excellent containment of the hazardous material released from the workspace above the downdraft table. However, increased airflow raises operation costs, so the airflow should be as low as feasible without compromising containment. The airflow is modeled using Reynolds Averaged Navier Stokes equations with a high Reynolds number k-epsilon turbulence model. CFD predictions are examined for several ventilation configurations. Based on this study, we find that substantial improvements in containment are possible concurrent with reduction in airflow, compared to the existing design of ventilation configuration.

Report number: LBNL-59266 Year: 2006

Title: Tracer Gas Transport under Mixed Convection Conditions in an Experimental Atrium: Comparison Between Experiments and CFD Predictions Published in: Atmospheric Environment, Volume 40, Pages 5236-5250.

Authors: Jayaraman, B., Finlayson, E.U., Sohn, M.D., Thatcher, T. L., Price, P. N., Wood, E. E., Sextro, R.G., Gadgil, A. J. Type: Journal Article

Abstract: We compare computational fluid dynamics (CFD) predictions using a steady-state Reynolds Averaged Navier-Stokes (RANS) model with experimental data on airflow and pollutant dispersion under mixed-convection conditions in a 7 x 9 x 11m high experimental facility. The Rayleigh number, based on height, was O(1011) and the atrium was mechanically ventilated. We released tracer gas in the atrium and measured the spatial distribution of concentrations; we then modeled the experiment using four different levels of modeling detail. The four computational models differ in the choice of temperature boundary conditions and the choice of turbulence model. Predictions from a low-Reynolds-number k- model with detailed boundary conditions agreed well with the data using three different model-measurement comparison metrics. Results from the same model with a single temperature prescribed for each wall also agreed well with the data. Predictions of a standard k- model were about the same as those of an isothermal model; neither performed well. Implications of the results for practical applications are discussed.

Report number: LBNL-56787 Year: 2005

Title: Sorption of organic gases in residential bedrooms and bathrooms Published in: 10th International Conference on Indoor Air Quality and Climate - Indoor Air 2005, Volume 2(9), Pages 2314-2319.

Authors: Singer, B.C., Hodgson, A., Hotchi, T., Ming, K.Y., Sextro, R., Wood, E. E., Brown, N.J. Type: Conference Proceedings

Report number: LBNL-55561 Year: 2005

Title: Investigation of Room Ventilation for Improved Operation of a Downdraft Table Published in: Proceedings of The 10th International Conference on Indoor Air Quality and Climate - Indoor Air 2005, Volume 3(1), Pages 2575-2579.

Authors: Jayaraman, B., Kristoffersen, A.R., Finlayson, E.O., Gadgil, A. Type: Conference Proceedings

Abstract: This paper reports a computational fluid dynamics (CFD) study on containment of airborne hazardous materials in a ventilated room containing a downdraft table. Specifically, we investigated the containment of hazardous airborne material under a range of ventilation configurations. The desirable ventilation configuration should ensure excellent containment of the hazardous material released from the workspace above the downdraft table. However, increased airflow raises operation costs, so the airflow should be as low as feasible without compromising containment. The airflow was modeled using Reynolds Averaged Navier Stokes equations with a high Reynolds number k-epsilon turbulence model using the commercial CFD code StarCD. CFD predictions were examined for several ventilation configurations. Based on this study, we found that substantial improvements in containment were possible with a significant reduction in airflow, compared to the existing ventilation configuration.

Report number: LBNL-57100 Year: 2005

Title: Comparison between experiments and CFD predictions of mixed convection flows in an atrium Published in: Proceedings of the 10th International Conference on Indoor Air Quality and Climate, Volume 3(3), Pages 2849-2853.

Authors: Jayaraman, B., Finlayson, E.O., Wood, E. E., Thatcher, T. L., Price, P. N., Sextro, R., Gadgil, A. Type: Conference Proceedings

Report number: LBNL-53943 Year: 2004

Title: Sorption of organic gases in a furnished room Published in: Atmospheric Environment, Volume 38, Pages 2483-2494.

Authors: Singer, B.C., Revzan, K., Hotchi, T., Hodgson, A., Brown, N.J. Type: Journal Article

Report number: LBNL-55321 Year: 2004

Title: Characterizing buildings for airflow models: What should we measure? Published in:

Authors: Price, P. N., Chang, S.C., Sohn, M.D. Type: Report

Abstract: Airflow models of buildings require dozens to hundreds of parameter values, depending on the complexity of the building and the level of fidelity desired for the model. Values for many of the parameters are usually subject to very large uncertainties (possibly an order of magnitude). Experiments can be used to calibrate or "tune" the model: input parameters can be adjusted until predicted quantities match observations. However, experimental time and equipment are always limited and some parameters are hard to measure, so it is generally impractical to perform an exhaustive set of measurements. Consequently, large uncertainties in some parameters typically remain even after tuning the model. We propose a method to help determine which measurements will maximally reduce the uncertainties in those input parameters that have the greatest influence on behavior of interest to researchers. Implications for experimental design are discussed.

Report number: LBNL-55083 Year: 2004

Title: Effect of room air recirculation delay on the decay rate of tracer gas Published in: 9th International Conference on Air Distribution in Rooms - RoomVent 2004, , Pages pp 6.

Authors: Kristoffersen, A.R., Gadgil, A., Lorenzetti, D. Type: Conference Proceedings

Report number: LBNL-56667 Year: 2004

Title: Coupled model for simulation of indoor airflow and pollutant transport Published in:

Authors: Jayaraman, B., Lorenzetti, D., Gadgil, A. Type: Report

Abstract: Understanding airflow in buildings is essential for improving energy efficiency, controlling airborne pollutants, and maintaining occupant comfort. Recent research on whole-building airflow simulation has turned toward protecting occupants from threats of chemical or biological agents. Sample applications include helping design systems to reduce exposure, and selecting optimal sensor locations.

Report number: LBNL-50105 Year: 2004

Title: Pollutant Dispersion in a Large Indoor Space Part 2 -- Computational Fluid Dyamics (CF) Predictions and Comparisons with a Model Experiment for Isothermal Flow Published in: Indoor Air, Volume 14, Pages 272-283.

Authors: Finlayson, E.U., Gadgil, A.J., Thatcher, T.L., Sextro, R.G. Type: Journal Article

Abstract: This paper reports on an investigation of the adequacy of Computational fluid dynamics (CFD), using a standard Reynolds Averaged Navier Stokes (RANS) model, for predicting dispersion of neutrally buoyant gas in a large indoor space. We used CFD to predict pollutant (dye) concentration profiles in a water filled scale model of an atrium with a continuous pollutant source. Predictions from the RANS formulation are comparable to an ensemble average of independent identical experiments. Model results were compared to pollutant concentration data in a horizontal plane from experiments in a scale model atrium. Predictions were made for steady-state (fully developed) and transient (developing) pollutant concentrations. Agreement between CFD predictions and ensemble averaged experimental measurements is quantified using the ratios of CFD-predicted and experimentally measured dye concentration at a large number of points in the measurement plane. Agreement is considered good if these ratios fall between 0.5 and 2.0 at all points in the plane. The standard k-epsilon two equation turbulence model obtains this level of agreement and predicts pollutant arrival time to the measurement plane within a few seconds. These results suggest that this modeling approach is adequate for predicting isothermal pollutant transport in a large room with simple geometry.

Report number: LBNL-50248 Year: 2003

Title: Pollutant Dispersion in a Large Indoor Space: Part 1 -- Scaled experiments using a water-filled model with occupants and furniture Published in: Indoor Air, Volume 14, Pages 258-271.

Authors: Thatcher, T.L., D.J. Wilson, E.E. Wood, M.J. Craig, R.G. Sextro Type: Journal Article

Abstract: Pollutant dispersion experiments were performed in a water-filled 30:1 scale model of a large room. Theoretical calculations were performed to confirm that the effects from losses of molecular diffusion, small scale eddies, turbulent kinetic energy, and turbulent mass diffusivity were minimal, even without matching Reynolds number between model and full scale. In the experiments, uranine dye was injected continuously from a small point source near the floor of the model. Pollutant concentrations were measured in a plane using laser induced fluorescence techniques. The concentration profiles were measured for three interior configurations for the model: unobstructed, table-like obstructions, and table- like and figure-like obstructions. The presence of objects in the model interior had a significant effect of both the concentration profile and fluctuation intensity in the measurement plane.

Report number: LBNL-47027 Year: 2003

Title: Comparing zonal and CFD models of air flows in large indoor spaces to experimental data Published in: Indoor Air, Volume 13, Pages 77-85.

Authors: Mora, L., Gadgil, A.J., Wurtz, E. Type: Journal Article

Abstract: It is inappropriate to use the assumption of instantaneously well-mixed zones to model airflows and pollutant transport in large indoor spaces. We investigate two approaches for describing the details of airflows in large indoor spaces, for accuracy and suitability for integration with multi-zone infiltration models. One approach, called the zonal method, was developed over the last 15 years to provide an improvement over the well-mixed assumption. The second approach is the use of a computational fluid dynamics simulation using a coarse grid model of the large indoor space. We compare velocity predictions from different formulations of zonal methods and coarse-grid k-e computational fluid dynamics (CFD) models, to measurements, in a 2D mechanically ventilated isothermal room. Our results suggest that, when airflow details are required, coarse-grid CFD is a better-suited method to predict airflows in large indoor spaces coupled with complex multi-zone buildings, than are the zonal methods. Based on the comparison of pressure predictions from different models, we offer guidance regarding the coupling of a model of detailed airflow in large spaces to algebraic multi-zone infiltration models.

Report number: LBNL-55772 Year: 2003

Title: Indoor Air Pollutants Part 1: General description of pollutants, levels and standards Published in: Air Infiltration and Ventilation Centre, Pages 1-12.

Authors: Levin, H. Type: Journal Article

Abstract: Pollutants found in indoor air are often several times higher than outdoors. Indoor air pollutants cause effects ranging from odor, annoyance, and irritation to illness, cancer, and even death. Since people spend the majority of their time indoors, it is important to recognize and control indoor air pollution. Some indoor air pollutants also adversely affect materials in the building and the building structure itself. The majority of indoor pollution comes from the building itself, its contents, or its occupants and their activities. Building materials and consumer products are important sources of indoor air pollutants. Some outdoor air pollutants enter with ventilation air. Interactions between substances in indoor air can also produce pollutants and some of these are more odorous, irritating, or hazardous than the chemicals that forms them. Reducing or eliminating pollution sources best achieves control of indoor air quality. Appropriate ventilation strategies can reduce concentrations of pollutants that can't be eliminated by source control.

Report number: LBNL-51413 Year: 2003

Title: Indoor Pollutant Mixing Time in an Isothermal Closed Room: An investigation using CFD Published in: Atmospheric Environment, Volume 37, Pages 5577-5586.

Authors: Gadgil, A.J., Lobscheid, C., Abadie, M.O., Finlayson, E.U. Type: Journal Article

Abstract: We report computational fluid dynamics (CFD) predictions of mixing time of a point pulse release of a pollutant in an unventilated mechanically mixed isothermal room. The aims of the study are to determine (1) the adequacy of the standard RANS two-equation (k-?) turbulence model to predict the mixing times under these conditions, and (2) the extent to which the mixing time is a feature of the room airflow, rather than the source location within the room. CFD simulations modeled the twelve mixing time experiments performed by Drescher et al. (1995) in an isothermal sealed room for a point pulse release. Predictions of mixing time were found in good agreement with experimental measurements, over an order of magnitude variation in blower power. Additional CFD simulations were performed to investigate the relation between pollutant mixing time and pollutant source location. Seventeen source locations were investigated for five different blower power configurations in the room. Results clearly show large dependence of the mixing time on the room airflow, with some dependence on source location. We further explore dependence of mixing time on the local airflow properties (velocity and turbulence intensity) at the source location. Implications for our findings for positioning air-toxic sensors in rooms are also discussed.

Report number: LBNL-53883 Year: 2003

Title: CFD Analysis of LLNL downdraft table Published in:

Authors: Finlayson, E.U., Jayaraman, B., Kristoffersen, A.R., Gadgil, A.J. Type: Report

Abstract: This study examines the airflow and contaminant transport in an existing room (89"x77"x98") that houses a downdraft table at LLNL. The facility was designed and built in the 1960's and is currently being considered for redesign. One objective of the redesign is to reduce airflow while maintaining or improving user safety. Because this facility has been used for many years to handle radioactive material it is impractical to conduct extensive experimental tests in it. Therefore, we have performed a Computational Fluid Dynamic (CFD) analysis of the facility. The study examines the current operational condition and some other cases with reduced airflow. Reducing airflow will lead to savings in operating costs (lower fan power consumption), and possible improvements in containment from reduced turbulence. In addition, we examine three design (geometry) changes. These are: (1) increasing the area of the HVAC inlet on the ceiling, (2) adding a 15? angled ceiling inlet and (3) increasing the area of the slot in the doorway. Of these three geometry modifications, only the larger doorway slot leads to improved predicted containment.

Report number: LBNL-53801 Year: 2003

Title: Data summary report of commercial building experiments in Salt Lake City, UT from May 17 to June 10, 2002 Published in:

Authors: Black, D.R., Thatcher, T.L., Delp, W.W., Derby, E.A., Chang, S.C., Sextro, R.G. Type: Report

Abstract: Under some circumstances, it may be desirable to provide all or part of a building with collective- protection against harmful chemical or biological (CB) agents. Collective-protection, as opposed to individual protection, uses the building -- its architecture, ventilation system, and control components -- to safeguard the health of the building occupants in the event of an indoor or outdoor release of toxic agents. In this study, we investigate the movement of tracer gases within a six-story building. The building was retrofitted to provide collective-protection on the upper two floors. To achieve this protection, the upper floors were over-pressurized using outside air that had passed through military specification carbon canisters and high-efficiency particulate air (HEPA) filters. The four lower floors were outside the collective-protection area and had a ventilation system that was retrofitted to provide response modes in the event of a CB release. These response modes (e.g. building flush and shelter in place) were designed to reduce the exposure of occupants on the lower floors without compromising the collective-protection zones. Over the course of four weeks, 16 tracer gas experiments were conducted to evaluate the collective- protection system (CPS) of the building's upper two floors and the ventilation response modes of the lower floors. Tracer gas concentrations were measured at a rate of 50 Hz in up to 30 locations in each experiment, which provided data with very high spatial and temporal resolution. Differential pressure and temperature measurements were also made throughout the building. Experiments showed that the CPS maintained a positive pressure differential between the upper two floors and the lower floors with various meteorological conditions and within specified settings of the HVAC fans serving the lower floors. However, the tracer experiments did show that a CB agent could enter the first zone of the decontamination areas on each CPS floor. Tracer gas analysis also showed that the shelter in place HVAC mode provided protection of lower floor occupants from an outdoor release by significantly lowering the air exchange rates on those floors. It was also determined that the efficacy of a flush mode triggered by an agent sensor depends greatly on the location of the sensor.

Report number: LBNL-47588 Year: 2002

Title: Rapidly locating and characterizing pollutant releases in buildings: An application of Bayesian data analysis Published in: Journal of the Air and Waste Management Association, Volume 52, Pages 1422-1432.

Authors: Sohn, M.D., Reynolds, P. , Singh, N. , Gadgil, A.J. Type: Journal Article

Abstract: Releases of airborne contaminants in or near a building can lead to significant human exposures unless prompt response measures are taken. However, possible responses can include conflicting strategies, such as shutting the ventilation system off versus running it in a purge mode, or having occupants evacuate versus sheltering in place. The proper choice depends in part on knowing the source locations, the amounts released, and the likely future dispersion routes of the pollutants. We present an approach that estimates this information in real time. It applies Bayesian statistics to interpret measurements of airborne pollutant concentrations from multiple sensors placed in the building and computes best estimates and uncertainties of the release conditions. The algorithm is fast, capable of continuously updating the estimates as measurements stream in from sensors. We demonstrate the approach using a hypothetical pollutant release in a five-room building. Unknowns to the interpretation algorithm include location, duration, and strength of the source, and some building and weather conditions. We examine two sensor sampling plans and three levels of data quality. Data interpretation in all examples is rapid; however, locating and characterizing the source with high probability depends on the amount and quality of data, and the sampling plan.

Report number: LBNL-49563 Year: 2002

Title: Rapidly Locating Sources And Predicting Contaminant Dispersion In Buildings Published in: Proceedings of the Indoor Air 2002 Conference, Monterey, CA, Volume 4, Pages 211-216.

Authors: Sohn, M.D., Reynolds, P., Gadgil, A.J., Sextro, R.G. Type: Conference Proceedings

Abstract: Contaminant releases in or near a building can lead to significant human exposures unless prompt response measures are taken. However, selecting the proper response depends in part on knowing the source locations, the amounts released, and the dispersion characteristics of the pollutants. We present an approach that estimates this information in real time. It uses Bayesian statistics to interpret measurements from sensors placed in the building yielding best estimates and uncertainties for the release conditions, including the operating state of the building. Because the method is fast, it continuously updates the estimates as measurements stream in from the sensors. We show preliminary results for characterizing a gas release in a three-floor, multi-room building at the Dugway Proving Grounds, Utah, USA.

Report number: LBNL-49537 Year: 2002

Title: Modeling the spread of anthrax in buildings Published in: Proceedings of the Indoor Air 2002 Conference, Monterey, CA, Volume 4, Pages 506-511.

Authors: Sextro, R.G., Lorenzetti, D.M., Sohn, M.D., Thatcher, T.L. Type: Conference Proceedings

Abstract: The recent contamination of several U.S. buildings by letters containing anthrax demonstrates the need to understand better the transport and fate of anthrax spores within buildings. We modeled the spread of anthrax for a hypothetical office suite and estimated the distribution of mass and resulting occupant exposures. Based on our modeling assumptions, more than 90% of the anthrax released remains in the building during the first 48 hours, with the largest fraction of the mass accumulating on floor surfaces where it is subject to tracking and resuspension. Although tracking and resuspension account for only a small amount of mass transfer, the model results suggests they can have an important effect on subsequent exposures. Additional research is necessary to understand and quantify these processes.

Report number: LBNL-49578 Year: 2002

Title: Assessing multizone airflow simulation software Published in: Proceedings of the Indoor Air 2002, Monterey, CA, Volume 1, Pages 267-271.

Authors: Lorenzetti, D.M. Type: Conference Proceedings

Abstract: Several standard multizone modeling programs, in order to improve their computational efficiency, make a number of simplifying assumptions. This paper examines how those assumptions reduce the solution times and memory use of the programs, but at the cost of restricting the models they can express. Applications where these restrictions may adversely affect the program's usefulness include: (1) natural ventilation, when buoyancy effects dominate mechanically-driven flow; (2) duct system design, when losses in T- junctions affect the system performance; and (3) control system design, when the dynamic transport of pollutants plays a significant role in the simulated system.

Report number: LBNL-46949 Year: 2002

Title: Computational Aspects of Nodal Multizone Airflow Systems Published in: Building and Environment, Volume 37, Pages 1083-1090.

Authors: Lorenzetti, D.M. Type: Journal Article

Abstract: The multizone approach to steady-state airflow problems models a building as a network of discrete mass flow paths. A nodal formulation of the problem writes the governing equations in terms of the unknown pressures at the points where the flow paths connect. This paper proves conditions under which the nodal equations yield symmetric positive-definite matrices, guaranteeing a unique solution to the flow network. It also establishes relaxed conditions under which a nodal airflow system yields asymmetric matrices with positive eigenvalues, guaranteeing at least one solution. Properly exploiting the system properties greatly reduces the cost of numerical solution. Thus, multizone airflow programs such as Contam and Comis depend on symmetric positive-definite systems. However, the background literature neglects or simplifies the underlying assumptions, does not assert existence and uniqueness, and even contains factual errors. This paper corrects those errors, states the implicit assumptions made in the programs, and discusses implications for modelers and programmers.

Report number: LBNL-51582 Year: 2002

Title: Predicting Indoor Pollutant Concentrations, and Applications to Air Quality Management Published in: Proceedings of the Joint WHO-JRC-ECA Workshop on the Role of Human Exposure Assessment in Air Quality Management, Bonn, Germany.

Authors: Lorenzetti, D.M. Type: Conference Proceedings

Abstract: Because most people spend more than 90% of their time indoors, predicting exposure to airborne pollutants requires models that incorporate the effect of buildings. Buildings affect the exposure of their occupants in a number of ways, both by design (for example, filters in ventilation systems remove particles) and incidentally (for example, sorption on walls can reduce peak concentrations, but prolong exposure to semivolatile organic compounds). Furthermore, building materials and occupant activities can generate pollutants. This paper surveys modeling approaches for predicting pollutant concentrations in buildings, and summarizes the application of these models.

Report number: LBNL-49457 Year: 2002

Title: Mixing of a point-source indoor pollution: Numerical predictions and comparison with experiments Published in: Proceedings of the Indoor Air 2002 Conference, Monterey, CA, Volume 4, Pages 223-228.

Authors: Lobscheid, C., Gadgil, A. J. Type: Conference Proceedings

Abstract: In most practical estimates of indoor pollutant exposures, it is common to assume that the pollutant is uniformly and instantaneously mixed in the indoor space. It is also commonly known that this assumption is simplistic, particularly for point sources, and for short-term or localized indoor exposures. We report computational fluid dynamics (CFD) predictions of mixing time of a point-pulse release of a pollutant in an unventilated mechanically mixed isothermal room. We aimed to determine the adequacy of the standard RANS two-equation (k-?) turbulence model to predict the mixing times under these conditions. The predictions were made for the twelve mixing time experiments performed by Drescher et al. (1995). We paid attention to adequate grid resolution, suppression of numerical diffusion, and careful simulation of the mechanical blowers used in the experiments. We found that the predictions are in good agreement with experimental measurements.

Report number: LBNL-49603 Year: 2002

Title: Modeling transient contaminant transport in HVAC systems and buildings Published in: Proceedings of the Indoor Air 2002 Conference, Monterey, CA, Volume 4, Pages 217-222.

Authors: Federspiel, C., H. Li, Auslander, D., Lorenzetti, D.M., Gadgil, A. J. Type: Conference Proceedings

Abstract: A mathematical model of the contaminant transport in HVAC systems and buildings is described. The model accounts for transients introduced by control elements such as fans and control dampers. The contaminant transport equations are coupled to momentum equations and mass continuity equations of the air. To avoid modeling variable transport delays directly, ducts are divided into a large number of small sections. Perfect mixing is assumed in each section. Contaminant transport equations are integrated with momentum equations in a way that guarantees mass continuity by using two non-negative velocities for computing the mass transport between elements. Computer simulations illustrate how the model may be used to analyze and design control systems that respond to a sudden release of a toxic contaminant near a building. By coupling transient flow prediction with transient contaminant prediction, the model overcomes a number of problems with existing contaminant transport codes.

Report number: LBNL-47653 Year: 2001

Title: Assessing Multizone Airflow Software Published in:

Authors: Lorenzetti, D.M. Type: Report

Abstract: Multizone models form the basis of most computer simulations of airflow and pollutant transport in buildings. In order to promote computational effciency, some multizone simulation programs, such as COMIS and CONTAM, restrict the form that their flow models may take. While these tools allow scientists and engineers to explore a wide range of building airflow problems, increasingly their use has led to new questions not answerable by the current generation of programs. This paper, directed at software developers working on the next generation of building airflow models, identifies structural aspects of COMIS and related programs that prevent them from easily incorporating desirable new airflow models. The paper also suggests criteria for evaluating alternate simulation environments for future modeling efforts.

Report number: LBNL-47785 Year: 2001

Title: Modeling pollutant penetration across building envelopes Published in: Atmospheric Environment, Volume 35, Pages 4451-4462.

Authors: Liu, D.L., Nazaroff, W.W. Type: Journal Article

Report number: LBNL-45542 Year: 2001

Title: Rapid Measurement and Mapping of Tracer Gas Concentrations in a Large Indoor Space Published in: Atmospheric Environment, Volume 35, Pages 2837-2844.

Authors: Fischer, M. L., Price, P. N., Thatcher, T. L., Schwalbe, C. A., Craig, M. J., Wood, E. E., Sextro, R. G., Gadgil, A. J. Type: Journal Article

Abstract: Rapid mapping of gas concentrations in air benefits studies of atmospheric phenomena ranging from pollutant dispersion to surface layer meteorology. Here we demonstrate a technique that combines multiple-open-path tunable-diode-laser (TDL) spectroscopy and computed tomography to map tracer gas concentrations with approximately 0.5 m spatial and 7 second temporal resolution. Releasing CH4 in a large (7m x 9m x 11m high) ventilated chamber, we measured path-integrated CH4 concentrations over a planar array of 28 "long" (2-10 m) optical paths, recording a complete sequence of measurements every 7 seconds during the course of hour-long experiments. Maps of CH4 concentration were reconstructed from the long-path data and compared with simultaneous measurements from 28 "short" (0.5 m) optical paths. On average, the reconstructed maps capture ~ 74% of the variance in the short path measurements. The accuracy of the reconstructed maps is limited, in large part, by the number of optical paths and the time required for the measurement. Straightforward enhancements to the instrumentation will allow rapid mapping of three-dimensional gas concentrations in indoor and outdoor air, with sub-second temporal resolution.

Report number: LBNL-48043 Year: 2000

Title: Reducing uncertainty in site characterization using Bayes Monte Carlo methods Published in: Journal of Environmental Engineering, Volume 126, Pages 893-902.

Authors: Sohn, M.D., Small, M.J. , Pantazidou, M. Type: Journal Article

Abstract: A Bayesian uncertainty analysis approach is developed as a tool for assessing and reducing uncertainty in ground-water flow and chemical transport predictions. The method is illustrated for a site contaminated with chlorinated hydrocarbons. Uncertainty in source characterization, in chemical transport parameters, and in the assumed hydrogeologic structure was evaluated using engineering judgment and updated using observed field data. The updating approach using observed hydraulic head data was able to differentiate between reasonable and unreasonable hydraulic conductivity fields but could not differentiate between alternative conceptual models for the geological structure of the subsurface at the site. Updating using observed chemical concentration data reduced the uncertainty in most parameters and reduced uncertainty in alternative conceptual models describing the geological structure at the site, source locations, and the chemicals released at these sources. Thirty-year transport projections for no-action and source containment scenarios demonstrate a typical application of the methods.

Report number: Year: 2000

Title: A novel technique to measure the magnitude and direction of flow in a tube Published in: Journal of Fluids Engineering, Volume 122, Pages 186-188.

Authors: Robinson, A.L., Sextro, R.G. Type: Journal Article

Report number: LBNL-46236 Year: 2000

Title: Algorithm for rapid tomography of gas concentrations Published in: Atmospheric Environment, Volume 35, Pages 2827-2835.

Authors: Price, P.N., Fischer, M.L., Gadgil, A.J., Sextro, R.G. Type: Journal Article

Report number: LBL-44792 Year: 2000

Title: Improving Speed and Robustness of the COMIS Solver Published in: Proceedings of the RoomVent 2000,7th International Conference on Air Distribution in Rooms, Reading, UK, Volume 1, Pages 241-246.

Authors: Lorenzetti, D.M., Sohn M.D. Type: Conference Proceedings

Abstract: The numerical investigation of airflow and chemical transport characteristics for a general class of buildings involves identifying values for model parameters, such as effective leakage areas and temperatures, for which a fair amount of uncertainty exists. A Monte Carlo simulation, with parameter values drawn from likely distributions using Latin Hypercube sampling, helps to account for these uncertainties by generating a corresponding distribution of simulated results. However, conducting large numbers of model runs can challenge a simulation program, not only by increasing the need for fast algorithms, but also by proposing specific combinations of parameter values that may define difficult numerical problems. The paper describes several numerical approaches to improving the speed and reliability of the COMIS multizone airflow simulation program. Selecting a broad class of algorithms based on the mathematical properties of the airflow systems (symmetry and positive-definiteness), it evaluates new solution methods for possible inclusion in the COMIS code. In addition, it discusses further changes that will likely appear in future releases of the program.

Report number: LBNL-44791 Year: 2000

Title: Pollutant transport and dispersion in large indoor spaces: A status report for the large space effort of the Interiors Project Published in:

Authors: Gadgil, A.G., Finlayson, E.U., Fischer, M.L., Price, P.N., Thatcher, T.L., Craig, M.J., Hong, K.H., Housman, J., Schwalbe, C.A., Wilson, D., Wood, E.E., Sextro, R.G. Type: Report

Report number: LBNL-42714 Year: 1999

Title: Measuring dispersion of gases in a large scale indoor environment using an open path tunable diode laser Published in: Proceedings of the Indoor Air '99, Edinburgh, Scotland, Volume 4, Pages 449-450.

Authors: Thatcher, T.L., Fischer, M.L., Price, P.N., Fisk, W.J., Gadgil, A.J., Sextro, R.G. Type: Conference Proceedings

Report number: LBNL-42708 Year: 1999

Title: Modeling aerosol behavior in multizone indoor environments Published in: Proceedings of the Indoor Air '99, Edinburgh, Scotland, Volume 4, Pages 785-790.

Authors: Sohn, M.D., A. Lai, B.V. Smith, R.G. Sextro, H.E. Feustel, W.W. Nazaroff Type: Conference Proceedings

Abstract: A publicly available aerosol dynamics model, MIAQ4, is coupled to a widely used multizone air flow and transport model, COMIS, to better understand and quantify the behavior of particles in indoor environments. MIAQ4 simulates the evolution of a size and chemically resolved particle distribution, including the effects of direct indoor emission, ventilation, filtration, deposition, and coagulation. COMIS predicts interzonal air-exchange rates based on pressure gradients (due to wind, buoyancy, and HVAC operation) and leaks between the zones and with the outside. The capabilities of the coupled system are demonstrated by predicting the transport of particles from two sources in a residence: environmental tobacco smoke (ETS) and particles generated from cooking. For ETS, MIAQ4 predicts particle size distributions that are similar to the emission source profile because ETS particles, concentrated in the size range 0.1 -- 1 ?m, are transformed by coagulation and deposition slowly compared with the rates of transport. For cooking, MIAQ4 predicts that the larger-sized particles will settle rapidly, causing a shift in size distribution as emissions are transported to other rooms.

Report number: LBNL-42712 Year: 1999

Title: Characterizing indoor airflow and pollutant transport using simulation modeling for prototypical buildings. 1. Office buildings Published in: Proceedings of the Indoor Air '99, Edinburgh, Scotland, Volume 4, Pages 719-724.

Authors: Sohn, M.D., J.M. Daisey, H.E. Feustel Type: Conference Proceedings

Abstract: This paper describes the first efforts at developing a set of prototypical buildings defined to capture the key features affecting airflow and pollutant transport in buildings. These buildings will be used to model airflow and pollutant transport for emergency response scenarios when limited site-specific information is available and immediate decisions must be made, and to better understand key features of buildings controlling occupant exposures to indoor pollutant sources. This paper presents an example of this approach for a prototypical intermediate-sized, open style, commercial building. Interzonal transport due to a short-term source release, e.g., accidental chemical spill, in the bottom and the upper floors is predicted and corresponding HVAC system operation effects and potential responses are considered. Three-hour average exposure estimates are used to compare effects of source location and HVAC operation.

Report number: LBNL-41005 Year: 1999

Title: Pollutant tomography using integrated concentration data from non-intersecting optical paths Published in: Atmospheric Environment, Volume 33, Pages 275-280.

Authors: Price, P.N. Type: Journal Article

Report number: Year: 1998

Title: Particle Deposition in a Two Dimensional Slot from a Transverse Stream Published in: Aerosol Science and Technology, Volume 28, Pages 235-246.

Authors: Carrie, F.R., Modera, M.P. Type: Journal Article

Report number: Year: 1997

Title: Stationary and Time-Dependent Indoor Tracer-Gas Concentration Profiles Measured by OP-FTIR Remote Sensing and SBFM Computed Tomography Published in: Atmospheric Environment, Volume 31, Pages 727-740.

Authors: Drescher, A.C., Park, D.Y., Yost, M.G., Gadgil, A.J., Levine, S.P., Nazaroff, W.W. Type: Journal Article

Report number: Year: 1996

Title: Gas-phase transport and sorption of benzene in soil Published in: Environmental Science and Technology, Volume 30, Pages 2178-2186.

Authors: Lin, T. F., Loy, M. D. V., Nazaroff, W. W. Type: Journal Article

Report number: Year: 1996

Title: Annex 23 -- An International Effort in Multizone Air Flow Modeling Published in: Proceedings of the RoomVent 1996, 5th International Conference on Air Distribution in Rooms, July 17 - 19, Yokohama, Japan, Volume 2, Pages 1-8.

Authors: Feustel, H.E. Type: Conference Proceedings

Report number: Year: 1996

Title: Novel Approach for Tomographic Reconstruction of Gas Concentration Distributions in Air: Use of Smooth Basis Functions and Simulated Annealing Published in: Atmospheric Environment, Volume 30, Pages 929-940.

Authors: Drescher, A.C., Gadgil, A.J., Price, P.N., Nazaroff, W.W. Type: Journal Article

Report number: LBL-36131 Year: 1995

Title: Indoor Airflow and Pollutant Removal in a Room With Floor-Based Task Ventilation: Results of Additional Experiments Published in: Building and Environment, Volume 30, Pages 323-332.

Authors: Faulkner, D., Fisk, W.J., Sullivan, D.P. Type: Journal Article

Report number: LBL-37895 Year: 1995

Title: Mixing of a Point Source Indoor Pollutant by Forced Convection Published in: Indoor Air, Volume 5, Pages 204-215.

Authors: Drescher, A.C., Lobascio, C., Gadgil, A.J., Nazaroff, W.W. Type: Journal Article

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Report number: LBNL-748E	Year: 2008
Title: Synthesis of Hectorite-TiO2 and Kaolinite-TiO2 Nanocomposites with Photocatalytic Activity for the Degradation of Model Air Pollutants	Published in: Submitted to Applied Clay Science.
Authors: Kibanova, D., Trejo, M., Destaillats, H., Cervini-Silva, J.	Type: Journal Article

Report number: LBNL-62082	Year: 2008
Title: Indoor pollutants emitted by office equipment: A review of reported data and information needs	Published in: Atmospheric Environment, Volume 42, Pages 1371-1388.
Authors: Destaillats, H., Maddalena, R.L., Singer, B.C., Hodgson, A.T., McKone, T.E.	Type: Journal Article

Report number:	Year: 2007
Title: Influence of indoor transport and mixing times scales on the performance of sensor systems for characterizing contaminant releases	Published in: Atmospheric Environment, Volume 41, Pages 9530-9542.
Authors: Sreedharan, P., Sohn, M.D., Nazaroff, W.W., Gadgil, A.J.	Type: Journal Article

Report number:	Year: 2007
Title: Effect of room air recirculation delay on the decay rate of tracer gas concentration,	Published in: Submitted to Indoor Air.
Authors: Lorenzetti, D.M., Kristoffersen, A.H., Gadgil, A.J.	Type: Journal Article

Report number: LBNL-62736	Year: 2007
Title: Filter loading corrections for real-time aethalometer measurements of fresh diesel soot. (2007)	Published in: Journal of Air and Waste Management Association, Volume 57, Pages 868–873.
Authors: Jimenez, J., Claiborn, C., Larson, T., Kirschtetter, T., Gundel, L.A.	Type: Journal Article

Report number:	Year: 2007
Title: Rapid Data Assimilation in the Indoor Environment: Theory and Examples from Real-time Interpretation of Indoor Plumes of Airborne Chemical	Published in: Pollution Modeling and its Applications XIX in press (2007)..
Authors: Gadgil, A.J., Sohn, M.D., Sreedharan, P., Borrego, C., Miranda, A.I.	Type: Book Section

Report number: LBNL-62107	Year: 2007
Title: Effectiveness of urban shelter-in-place. II: Residential Districts	Published in: Atmospheric Environment, Volume 41, Pages 7082-7095.
Authors: Chan, W.R., Nazaroff, W.W., Price, P.N., Gadgil, A.J.	Type: Journal Article

Report number: LBNL-61686	Year: 2007
Title: Effectiveness of Urban Shelter-in-Place I: Idealized Conditions	Published in: Atmospheric Environment, Volume 41, Pages 4962-4976 .
Authors: Chan, W.R., Nazaroff, W.W., Price, P. N., Gadgil, A.J.	Type: Journal Article

Report number:	Year: 2006
Title: An Attic-Interior Infiltration and Interzone Transport Model of a House	Published in: Building and Environment, Volume 40, Pages 701-718.
Authors: Walker, I.S., Forest, T.W., Wilson, D.J.	Type: Journal Article

Report number: LBNL-57385	Year: 2006
Title: CFD Investigation of Room Ventilation for Improved Operation of a Downdraft Table: Novel Concepts	Published in: Journal of Occupational and Environmental Hygiene, Volume 3, Pages 583-591.
Authors: Jayaraman, B., Kristoffersen, A.H., Finlayson, E.U., Gadgil, A.J.	Type: Journal Article
Abstract: We report a computational fluid dynamics (CFD) study of containment of airborne hazardous materials in a ventilated room containing a downdraft table. Specifically, we investigate the containment of hazardous airborne material obtainable under a range of ventilation configurations. The desirable ventilation configuration should ensure excellent containment of the hazardous material released from the workspace above the downdraft table. However, increased airflow raises operation costs, so the airflow should be as low as feasible without compromising containment. The airflow is modeled using Reynolds Averaged Navier Stokes equations with a high Reynolds number k-epsilon turbulence model. CFD predictions are examined for several ventilation configurations. Based on this study, we find that substantial improvements in containment are possible concurrent with reduction in airflow, compared to the existing design of ventilation configuration.

Report number: LBNL-59266	Year: 2006
Title: Tracer Gas Transport under Mixed Convection Conditions in an Experimental Atrium: Comparison Between Experiments and CFD Predictions	Published in: Atmospheric Environment, Volume 40, Pages 5236-5250.
Authors: Jayaraman, B., Finlayson, E.U., Sohn, M.D., Thatcher, T. L., Price, P. N., Wood, E. E., Sextro, R.G., Gadgil, A. J.	Type: Journal Article
Abstract: We compare computational fluid dynamics (CFD) predictions using a steady-state Reynolds Averaged Navier-Stokes (RANS) model with experimental data on airflow and pollutant dispersion under mixed-convection conditions in a 7 x 9 x 11m high experimental facility. The Rayleigh number, based on height, was O(1011) and the atrium was mechanically ventilated. We released tracer gas in the atrium and measured the spatial distribution of concentrations; we then modeled the experiment using four different levels of modeling detail. The four computational models differ in the choice of temperature boundary conditions and the choice of turbulence model. Predictions from a low-Reynolds-number k- model with detailed boundary conditions agreed well with the data using three different model-measurement comparison metrics. Results from the same model with a single temperature prescribed for each wall also agreed well with the data. Predictions of a standard k- model were about the same as those of an isothermal model; neither performed well. Implications of the results for practical applications are discussed.

Report number: LBNL-56787	Year: 2005
Title: Sorption of organic gases in residential bedrooms and bathrooms	Published in: 10th International Conference on Indoor Air Quality and Climate - Indoor Air 2005, Volume 2(9), Pages 2314-2319.
Authors: Singer, B.C., Hodgson, A., Hotchi, T., Ming, K.Y., Sextro, R., Wood, E. E., Brown, N.J.	Type: Conference Proceedings

Report number: LBNL-55561	Year: 2005
Title: Investigation of Room Ventilation for Improved Operation of a Downdraft Table	Published in: Proceedings of The 10th International Conference on Indoor Air Quality and Climate - Indoor Air 2005, Volume 3(1), Pages 2575-2579.
Authors: Jayaraman, B., Kristoffersen, A.R., Finlayson, E.O., Gadgil, A.	Type: Conference Proceedings
Abstract: This paper reports a computational fluid dynamics (CFD) study on containment of airborne hazardous materials in a ventilated room containing a downdraft table. Specifically, we investigated the containment of hazardous airborne material under a range of ventilation configurations. The desirable ventilation configuration should ensure excellent containment of the hazardous material released from the workspace above the downdraft table. However, increased airflow raises operation costs, so the airflow should be as low as feasible without compromising containment. The airflow was modeled using Reynolds Averaged Navier Stokes equations with a high Reynolds number k-epsilon turbulence model using the commercial CFD code StarCD. CFD predictions were examined for several ventilation configurations. Based on this study, we found that substantial improvements in containment were possible with a significant reduction in airflow, compared to the existing ventilation configuration.

Report number: LBNL-57100	Year: 2005
Title: Comparison between experiments and CFD predictions of mixed convection flows in an atrium	Published in: Proceedings of the 10th International Conference on Indoor Air Quality and Climate, Volume 3(3), Pages 2849-2853.
Authors: Jayaraman, B., Finlayson, E.O., Wood, E. E., Thatcher, T. L., Price, P. N., Sextro, R., Gadgil, A.	Type: Conference Proceedings

Report number: LBNL-53943	Year: 2004
Title: Sorption of organic gases in a furnished room	Published in: Atmospheric Environment, Volume 38, Pages 2483-2494.
Authors: Singer, B.C., Revzan, K., Hotchi, T., Hodgson, A., Brown, N.J.	Type: Journal Article

Report number: LBNL-55321	Year: 2004
Title: Characterizing buildings for airflow models: What should we measure?	Published in:
Authors: Price, P. N., Chang, S.C., Sohn, M.D.	Type: Report
Abstract: Airflow models of buildings require dozens to hundreds of parameter values, depending on the complexity of the building and the level of fidelity desired for the model. Values for many of the parameters are usually subject to very large uncertainties (possibly an order of magnitude). Experiments can be used to calibrate or "tune" the model: input parameters can be adjusted until predicted quantities match observations. However, experimental time and equipment are always limited and some parameters are hard to measure, so it is generally impractical to perform an exhaustive set of measurements. Consequently, large uncertainties in some parameters typically remain even after tuning the model. We propose a method to help determine which measurements will maximally reduce the uncertainties in those input parameters that have the greatest influence on behavior of interest to researchers. Implications for experimental design are discussed.

Report number: LBNL-55083	Year: 2004
Title: Effect of room air recirculation delay on the decay rate of tracer gas	Published in: 9th International Conference on Air Distribution in Rooms - RoomVent 2004, , Pages pp 6.
Authors: Kristoffersen, A.R., Gadgil, A., Lorenzetti, D.	Type: Conference Proceedings

Report number: LBNL-56667	Year: 2004
Title: Coupled model for simulation of indoor airflow and pollutant transport	Published in:
Authors: Jayaraman, B., Lorenzetti, D., Gadgil, A.	Type: Report
Abstract: Understanding airflow in buildings is essential for improving energy efficiency, controlling airborne pollutants, and maintaining occupant comfort. Recent research on whole-building airflow simulation has turned toward protecting occupants from threats of chemical or biological agents. Sample applications include helping design systems to reduce exposure, and selecting optimal sensor locations.

Report number: LBNL-50105	Year: 2004
Title: Pollutant Dispersion in a Large Indoor Space Part 2 -- Computational Fluid Dyamics (CF) Predictions and Comparisons with a Model Experiment for Isothermal Flow	Published in: Indoor Air, Volume 14, Pages 272-283.
Authors: Finlayson, E.U., Gadgil, A.J., Thatcher, T.L., Sextro, R.G.	Type: Journal Article
Abstract: This paper reports on an investigation of the adequacy of Computational fluid dynamics (CFD), using a standard Reynolds Averaged Navier Stokes (RANS) model, for predicting dispersion of neutrally buoyant gas in a large indoor space. We used CFD to predict pollutant (dye) concentration profiles in a water filled scale model of an atrium with a continuous pollutant source. Predictions from the RANS formulation are comparable to an ensemble average of independent identical experiments. Model results were compared to pollutant concentration data in a horizontal plane from experiments in a scale model atrium. Predictions were made for steady-state (fully developed) and transient (developing) pollutant concentrations. Agreement between CFD predictions and ensemble averaged experimental measurements is quantified using the ratios of CFD-predicted and experimentally measured dye concentration at a large number of points in the measurement plane. Agreement is considered good if these ratios fall between 0.5 and 2.0 at all points in the plane. The standard k-epsilon two equation turbulence model obtains this level of agreement and predicts pollutant arrival time to the measurement plane within a few seconds. These results suggest that this modeling approach is adequate for predicting isothermal pollutant transport in a large room with simple geometry.

Report number: LBNL-50248	Year: 2003
Title: Pollutant Dispersion in a Large Indoor Space: Part 1 -- Scaled experiments using a water-filled model with occupants and furniture	Published in: Indoor Air, Volume 14, Pages 258-271.
Authors: Thatcher, T.L., D.J. Wilson, E.E. Wood, M.J. Craig, R.G. Sextro	Type: Journal Article
Abstract: Pollutant dispersion experiments were performed in a water-filled 30:1 scale model of a large room. Theoretical calculations were performed to confirm that the effects from losses of molecular diffusion, small scale eddies, turbulent kinetic energy, and turbulent mass diffusivity were minimal, even without matching Reynolds number between model and full scale. In the experiments, uranine dye was injected continuously from a small point source near the floor of the model. Pollutant concentrations were measured in a plane using laser induced fluorescence techniques. The concentration profiles were measured for three interior configurations for the model: unobstructed, table-like obstructions, and table- like and figure-like obstructions. The presence of objects in the model interior had a significant effect of both the concentration profile and fluctuation intensity in the measurement plane.

Report number: LBNL-47027	Year: 2003
Title: Comparing zonal and CFD models of air flows in large indoor spaces to experimental data	Published in: Indoor Air, Volume 13, Pages 77-85.
Authors: Mora, L., Gadgil, A.J., Wurtz, E.	Type: Journal Article
Abstract: It is inappropriate to use the assumption of instantaneously well-mixed zones to model airflows and pollutant transport in large indoor spaces. We investigate two approaches for describing the details of airflows in large indoor spaces, for accuracy and suitability for integration with multi-zone infiltration models. One approach, called the zonal method, was developed over the last 15 years to provide an improvement over the well-mixed assumption. The second approach is the use of a computational fluid dynamics simulation using a coarse grid model of the large indoor space. We compare velocity predictions from different formulations of zonal methods and coarse-grid k-e computational fluid dynamics (CFD) models, to measurements, in a 2D mechanically ventilated isothermal room. Our results suggest that, when airflow details are required, coarse-grid CFD is a better-suited method to predict airflows in large indoor spaces coupled with complex multi-zone buildings, than are the zonal methods. Based on the comparison of pressure predictions from different models, we offer guidance regarding the coupling of a model of detailed airflow in large spaces to algebraic multi-zone infiltration models.

Report number: LBNL-55772	Year: 2003
Title: Indoor Air Pollutants Part 1: General description of pollutants, levels and standards	Published in: Air Infiltration and Ventilation Centre, Pages 1-12.
Authors: Levin, H.	Type: Journal Article
Abstract: Pollutants found in indoor air are often several times higher than outdoors. Indoor air pollutants cause effects ranging from odor, annoyance, and irritation to illness, cancer, and even death. Since people spend the majority of their time indoors, it is important to recognize and control indoor air pollution. Some indoor air pollutants also adversely affect materials in the building and the building structure itself. The majority of indoor pollution comes from the building itself, its contents, or its occupants and their activities. Building materials and consumer products are important sources of indoor air pollutants. Some outdoor air pollutants enter with ventilation air. Interactions between substances in indoor air can also produce pollutants and some of these are more odorous, irritating, or hazardous than the chemicals that forms them. Reducing or eliminating pollution sources best achieves control of indoor air quality. Appropriate ventilation strategies can reduce concentrations of pollutants that can't be eliminated by source control.

Report number: LBNL-51413	Year: 2003
Title: Indoor Pollutant Mixing Time in an Isothermal Closed Room: An investigation using CFD	Published in: Atmospheric Environment, Volume 37, Pages 5577-5586.
Authors: Gadgil, A.J., Lobscheid, C., Abadie, M.O., Finlayson, E.U.	Type: Journal Article
Abstract: We report computational fluid dynamics (CFD) predictions of mixing time of a point pulse release of a pollutant in an unventilated mechanically mixed isothermal room. The aims of the study are to determine (1) the adequacy of the standard RANS two-equation (k-?) turbulence model to predict the mixing times under these conditions, and (2) the extent to which the mixing time is a feature of the room airflow, rather than the source location within the room. CFD simulations modeled the twelve mixing time experiments performed by Drescher et al. (1995) in an isothermal sealed room for a point pulse release. Predictions of mixing time were found in good agreement with experimental measurements, over an order of magnitude variation in blower power. Additional CFD simulations were performed to investigate the relation between pollutant mixing time and pollutant source location. Seventeen source locations were investigated for five different blower power configurations in the room. Results clearly show large dependence of the mixing time on the room airflow, with some dependence on source location. We further explore dependence of mixing time on the local airflow properties (velocity and turbulence intensity) at the source location. Implications for our findings for positioning air-toxic sensors in rooms are also discussed.

Report number: LBNL-53883	Year: 2003
Title: CFD Analysis of LLNL downdraft table	Published in:
Authors: Finlayson, E.U., Jayaraman, B., Kristoffersen, A.R., Gadgil, A.J.	Type: Report
Abstract: This study examines the airflow and contaminant transport in an existing room (89"x77"x98") that houses a downdraft table at LLNL. The facility was designed and built in the 1960's and is currently being considered for redesign. One objective of the redesign is to reduce airflow while maintaining or improving user safety. Because this facility has been used for many years to handle radioactive material it is impractical to conduct extensive experimental tests in it. Therefore, we have performed a Computational Fluid Dynamic (CFD) analysis of the facility. The study examines the current operational condition and some other cases with reduced airflow. Reducing airflow will lead to savings in operating costs (lower fan power consumption), and possible improvements in containment from reduced turbulence. In addition, we examine three design (geometry) changes. These are: (1) increasing the area of the HVAC inlet on the ceiling, (2) adding a 15? angled ceiling inlet and (3) increasing the area of the slot in the doorway. Of these three geometry modifications, only the larger doorway slot leads to improved predicted containment.

Report number: LBNL-53801	Year: 2003
Title: Data summary report of commercial building experiments in Salt Lake City, UT from May 17 to June 10, 2002	Published in:
Authors: Black, D.R., Thatcher, T.L., Delp, W.W., Derby, E.A., Chang, S.C., Sextro, R.G.	Type: Report
Abstract: Under some circumstances, it may be desirable to provide all or part of a building with collective- protection against harmful chemical or biological (CB) agents. Collective-protection, as opposed to individual protection, uses the building -- its architecture, ventilation system, and control components -- to safeguard the health of the building occupants in the event of an indoor or outdoor release of toxic agents. In this study, we investigate the movement of tracer gases within a six-story building. The building was retrofitted to provide collective-protection on the upper two floors. To achieve this protection, the upper floors were over-pressurized using outside air that had passed through military specification carbon canisters and high-efficiency particulate air (HEPA) filters. The four lower floors were outside the collective-protection area and had a ventilation system that was retrofitted to provide response modes in the event of a CB release. These response modes (e.g. building flush and shelter in place) were designed to reduce the exposure of occupants on the lower floors without compromising the collective-protection zones. Over the course of four weeks, 16 tracer gas experiments were conducted to evaluate the collective- protection system (CPS) of the building's upper two floors and the ventilation response modes of the lower floors. Tracer gas concentrations were measured at a rate of 50 Hz in up to 30 locations in each experiment, which provided data with very high spatial and temporal resolution. Differential pressure and temperature measurements were also made throughout the building. Experiments showed that the CPS maintained a positive pressure differential between the upper two floors and the lower floors with various meteorological conditions and within specified settings of the HVAC fans serving the lower floors. However, the tracer experiments did show that a CB agent could enter the first zone of the decontamination areas on each CPS floor. Tracer gas analysis also showed that the shelter in place HVAC mode provided protection of lower floor occupants from an outdoor release by significantly lowering the air exchange rates on those floors. It was also determined that the efficacy of a flush mode triggered by an agent sensor depends greatly on the location of the sensor.

Report number: LBNL-47588	Year: 2002
Title: Rapidly locating and characterizing pollutant releases in buildings: An application of Bayesian data analysis	Published in: Journal of the Air and Waste Management Association, Volume 52, Pages 1422-1432.
Authors: Sohn, M.D., Reynolds, P. , Singh, N. , Gadgil, A.J.	Type: Journal Article
Abstract: Releases of airborne contaminants in or near a building can lead to significant human exposures unless prompt response measures are taken. However, possible responses can include conflicting strategies, such as shutting the ventilation system off versus running it in a purge mode, or having occupants evacuate versus sheltering in place. The proper choice depends in part on knowing the source locations, the amounts released, and the likely future dispersion routes of the pollutants. We present an approach that estimates this information in real time. It applies Bayesian statistics to interpret measurements of airborne pollutant concentrations from multiple sensors placed in the building and computes best estimates and uncertainties of the release conditions. The algorithm is fast, capable of continuously updating the estimates as measurements stream in from sensors. We demonstrate the approach using a hypothetical pollutant release in a five-room building. Unknowns to the interpretation algorithm include location, duration, and strength of the source, and some building and weather conditions. We examine two sensor sampling plans and three levels of data quality. Data interpretation in all examples is rapid; however, locating and characterizing the source with high probability depends on the amount and quality of data, and the sampling plan.

Report number: LBNL-49563	Year: 2002
Title: Rapidly Locating Sources And Predicting Contaminant Dispersion In Buildings	Published in: Proceedings of the Indoor Air 2002 Conference, Monterey, CA, Volume 4, Pages 211-216.
Authors: Sohn, M.D., Reynolds, P., Gadgil, A.J., Sextro, R.G.	Type: Conference Proceedings
Abstract: Contaminant releases in or near a building can lead to significant human exposures unless prompt response measures are taken. However, selecting the proper response depends in part on knowing the source locations, the amounts released, and the dispersion characteristics of the pollutants. We present an approach that estimates this information in real time. It uses Bayesian statistics to interpret measurements from sensors placed in the building yielding best estimates and uncertainties for the release conditions, including the operating state of the building. Because the method is fast, it continuously updates the estimates as measurements stream in from the sensors. We show preliminary results for characterizing a gas release in a three-floor, multi-room building at the Dugway Proving Grounds, Utah, USA.

Report number: LBNL-49537	Year: 2002
Title: Modeling the spread of anthrax in buildings	Published in: Proceedings of the Indoor Air 2002 Conference, Monterey, CA, Volume 4, Pages 506-511.
Authors: Sextro, R.G., Lorenzetti, D.M., Sohn, M.D., Thatcher, T.L.	Type: Conference Proceedings
Abstract: The recent contamination of several U.S. buildings by letters containing anthrax demonstrates the need to understand better the transport and fate of anthrax spores within buildings. We modeled the spread of anthrax for a hypothetical office suite and estimated the distribution of mass and resulting occupant exposures. Based on our modeling assumptions, more than 90% of the anthrax released remains in the building during the first 48 hours, with the largest fraction of the mass accumulating on floor surfaces where it is subject to tracking and resuspension. Although tracking and resuspension account for only a small amount of mass transfer, the model results suggests they can have an important effect on subsequent exposures. Additional research is necessary to understand and quantify these processes.

Report number: LBNL-49578	Year: 2002
Title: Assessing multizone airflow simulation software	Published in: Proceedings of the Indoor Air 2002, Monterey, CA, Volume 1, Pages 267-271.
Authors: Lorenzetti, D.M.	Type: Conference Proceedings
Abstract: Several standard multizone modeling programs, in order to improve their computational efficiency, make a number of simplifying assumptions. This paper examines how those assumptions reduce the solution times and memory use of the programs, but at the cost of restricting the models they can express. Applications where these restrictions may adversely affect the program's usefulness include: (1) natural ventilation, when buoyancy effects dominate mechanically-driven flow; (2) duct system design, when losses in T- junctions affect the system performance; and (3) control system design, when the dynamic transport of pollutants plays a significant role in the simulated system.

Report number: LBNL-46949	Year: 2002
Title: Computational Aspects of Nodal Multizone Airflow Systems	Published in: Building and Environment, Volume 37, Pages 1083-1090.
Authors: Lorenzetti, D.M.	Type: Journal Article
Abstract: The multizone approach to steady-state airflow problems models a building as a network of discrete mass flow paths. A nodal formulation of the problem writes the governing equations in terms of the unknown pressures at the points where the flow paths connect. This paper proves conditions under which the nodal equations yield symmetric positive-definite matrices, guaranteeing a unique solution to the flow network. It also establishes relaxed conditions under which a nodal airflow system yields asymmetric matrices with positive eigenvalues, guaranteeing at least one solution. Properly exploiting the system properties greatly reduces the cost of numerical solution. Thus, multizone airflow programs such as Contam and Comis depend on symmetric positive-definite systems. However, the background literature neglects or simplifies the underlying assumptions, does not assert existence and uniqueness, and even contains factual errors. This paper corrects those errors, states the implicit assumptions made in the programs, and discusses implications for modelers and programmers.