IAQ Model For Windows:RISK
Indoor Environment Management Branch
Mission of IAQ Engineering Program
- Develop cost-effective tools, techniques, technologies, and guidance necessary to prevent or reduce individual exposure to indoor air pollutants.
Role of modeling program
- Provide tools to integrate the results of IAQ research.
- Provide tools for analysis of the effects of IAQ control options on individual exposure.
- Provide tools for understanding interactions of sources, sinks, ventilation, building parameters, air cleaners, and individual activity patterns on individual exposure.
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Model Design
- Individual rooms are well mixed
- Well confirmed assumption for time scales of interest (several tens of minutes).
- Building as a whole does not have to be well mixed.
Modeling decisions
- The emphasis of the effort was on model ease of use.
- The data requirements were minimized as much as possible.
- Results of ongoing research on sources, sinks, ventilation, and air cleaners was incorporated into model as soon as possible.
Modeling decisions (Cont.)
- User responsible for consistent data input e.g.:
- User responsible for balancing flows.
- User responsible for consistent units.
Model limitations
- Data limitations
- Limited data on source emission rates.
- Limited data and understanding of sinks.
- Limited risk data.
- Limited library of default data for room-to-room air flows, ventilation, etc.
Model limitations (Cont.)
- User limitations
- User does not understand what model can and can not do.
- User does not have clear idea of the question the model should address.
- User does not have adequate input data
- User does not understand model output.
Model organization
- Building: contains all fixed information about building.
- Number of rooms.
- Size of rooms.
- Location of rooms.
Model organization (Cont.)
- Scenario: contains all variable information
- Ventilation rates.
- Source and sink information.
- Activity patterns.
- Room-to-room air flows
Model equations
Types of sources
- Steady state sources
- Long term such as moth cakes
- Short term such as aerosol sprays
- Decaying sources
- Short term decay due to evaporation
- Long term decay due to diffusion
Source models-Empirical
Source models-empirical
Source models-empirical
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Gas-phase Mass Transfer Rate:
Source-phase Mass Transfer Rate:
Source models-mass transfer
Sink model
Exposure
Types of Risk
- Cancer (usually related to cumulative exposure)
- Chronic (often related to cumulative exposure above a threshold)
Risk Calculation Procedure
Comparison with data
- Quantitative comparison (ASTM criteria)
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Comparison of predictions and data
Comparison of predictions and data
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ASTM Criteria
- Slope of line for predicted versus measured should be between 0.75 and 1.25.
- Intercept of line for predicted versus measured should be ញ% of average of measured
- Correlation coefficient of predicted and measured should be > 0.9
ASTM Criteria (Continued)
- Normalized mean squared error <= 0.25
- Fractional bias absolute value < 0.25
ASTM Criteria Normalized Mean Squared Error
ASTM Criteria: Bias
Comparison for tracer gas
Comparison for various sources
Conclusions
- Model design goals mostly met
- Model predictions in good agreement with test house data
- Source models developed using chambers provide good predictions when used with IAQ model
- Sink terms are major source of uncertainty