The Airflow and Pollutant transport Group studies airflow in buildings, and the resulting distribution of pollutants. To this end, the group combines
field experiments, chamber studies,
and simulations with both whole-building and
detailed room models.
The airflow patterns in a building affect its occupants in many ways:
Air quality.
Good air quality demands a sufficient supply of clean air, to sweep pollutants out of occupied spaces. Airborne pollutants include gases, such as carbon dioxide, and
particles, such as cat dander. These pollutants may have sources both inside and
outside the building, so airflows across the building envelope can matter as much as the
flows from room to room. LBNL's Indoor Environment Department
conducts research across a wide spectrum of air quality issues.
Life safety.
Traditionally, life safety in the building airflow context meant smoke control. More recently, protection against chemical, biological, or radiological CBR) attacks
has gained in importance. Because air currents can rapidly transport these agents throughout a building, understanding airflow patterns is essential to protecting
building occupants from both accidental and intentional releases.
Energy use.
For many buildings, the cost of heating and cooling outdoor air constitutes a large component of energy use. Outdoor air enters a building either intentionally, for
example in a ducted ventilation system used to provide fresh air, or unintentionally, for example by infiltration through poorly-sealed doors, or through cracks in
the building facade. LBNL's Energy Analysis Department
conducts research, and provides information, on this and other important energy issues in buildings. In addition, the
Simulation Research Group develops software, such as EnergyPlus and SPARK,
targeted at building energy applications. EnergyPlus contains a link to the COMIS
multizone airflow model.
Thermal comfort.
Many buildings use their ventilation system not only to provide fresh air to the occupied spaces, but also to heat and cool the rooms as needed. Furthermore, people's
thermal comfort depends on the humidity of the air, the local air speed, and temperature stratification. The building's ventilation system helps set all these conditions.
Tools for Airflow Research
The Airflow and Pollutant Transport Group combines simulation and experiments to understand airflow in buildings.
Experimental work includes field studies, such as our intensive investigations of buildings during the
Joint Urban 2003 exercises in Oklahoma City. We also conduct
laboratory-scale experiments, for example to understand particle deposition in ducts and in walls,
to study mixing in rooms, and to understand tracking of particles by human activity.
Simulation tools for airflow research fall into three categories, based on their level of detail:
Box models.
Box models start with analytical solutions to simple pollutant transport problems, and apply them to regional-scale problems. For example, our work on protecting residences from
outdoor plumes treats a house as a single, well-mixed space, and uses statistical methods to estimate
the distribution of infiltration values across all homes in a geographical area. This simple model helps emergency planners respond to an outdoor release of pollutant, for
example comparing evacuation and various shelter-in-place strategies.
Multizone models.
For more complex buildings, or to study details of flow from room to room, multizone models
idealize a whole building as a collection of well-mixed spaces, linked by flow paths. These models calculate zone-to-zone flows using engineering correlations, and estimate the
resulting distribution of pollutant within the building. They also can solve problems of infiltration and exfiltration.
Computational Fluid Dynamics models.
At the greatest level of detail, CFD programs find airflows within rooms. CFD techniques can estimate
the degree of mixing or stratification within a room, and can determine where air currents will carry a pollutant, based on its point of release within a room. Unfortunately,
CFD is too expensive, computationally, to apply to entire buildings.
Specific Research Interests
The Airflow and Pollutant Transport Group mainly studies building airflow in order to support our other research interests. For example:
CBR Protection/Planning.
Our advice on protecting buildings against a chemical or biological (CB) attack comes,
in part, from considering how airflows transport pollutants through buildings. In general, our research on
planning and first response guidance draws on all our experimental and computational work on building airflows.
Sensor interpretation.
This research relies on building airflow models in two ways. First, our sensor interpretation
algorithms work by examining pollutant concentration measurements as they come in from building sensors, and matching them against pre-existing libraries of concentration predictions.
The libraries result from simulating the building under a large number of operating conditions, and with multiple values for the unknown parameters. Second, we test the interpretation
algorithms using simulation models.
Particle transport.
Airflow constitutes one of the major driving forces that transport particles through buildings. Many of our experimental
work relates to this topic, and we develop and use simulation tools to support particle-tracking studies.
Uncertainty analysis.
Providing guidance on emergency response to pollutant releases in or around buildings requires an understanding of how one building differs from another, and how day-to-day changes in a
building's operation and use can affect its airflows. Thus our uncertainty analysis efforts use statistical techniques
to study the effect of assumptions about unknown model parameters on the model results. In a like manner, our experimental work seeks to replicate experiments, where possible, in order
to understand the natural variation in building systems.
Work on simulation tools includes the improvement of our multizone model, COMIS,
and the use of Computational Fluid Dynamics to scope further improvements to COMIS. In addition, we perform research on
integrating simulation tools, for example combining CFD and multizone approaches, and making COMIS available
as a subroutine for other programs to use.
