Models have been used for centuries to evaluate and refine designs before construction and production. Models help architects see how a building fits into the surrounding environment, evaluate interior space and identify potential construction problems. Engineers build and test models to help refine the design of ships, aircraft, automobiles and other complex products.
Computers greatly enhance the modeling process. Computers generate virtual three-dimensional models faster, cheaper and in more detail than actual physical models. Computer models are also more versatile. Designers and customers can "walk" through and around a virtual model to develop a better understanding of a design and its limitations.
Computers can do more than simply replace physical models. Computers bring mathematical models of the physical world to life to simulate how a design will behave in the real world. These models can quickly assess the impact of "what if" changes in new designs and also help track down problems in existing designs.
The National Institute of Standards and Technology's (NIST) Building and Fire Research Laboratory (www.bfrl.nist.gov) is a leader in developing computer models to improve public and worker safety and health. While much of the laboratory's work is research related, one application in particular, CONTAMW, has practical safety and health applications.
CONTAMW is an indoor air quality and ventilation analysis program designed to predict air flows, contamination concentrations and building occupant exposure to airborne contaminants. The airflow model includes air infiltration through walls, windows, and doors; air flows driven by mechanical ventilation systems; wind effects; and indoor and outdoor temperature differences.
Modeling a building begins with drawing the building floor plan on the CONTAMW "sketch pad" (Figure 1). This floor plan consists of defined "zones" -- basically a room or space within a building with a uniform temperature and contaminant concentration. "Airflow paths," doors, windows and other building components that allow air to move between zones, are added next.
Defining the building heating ventilation and air conditioning (HVAC) system completes the model. An HVAC system can be built by drawing the actual duct work including detailed air handler specifications, or by using CONTAMW's Simple Air Handling System.
Predicting contaminant concentrations involves adding contaminant sources with a known or estimated generation rate. Then, based upon modeled air flows, CONTAMW models the dispersal of the airborne contaminants and occupant exposures. The software supports the impact of chemical reactions, adsorption, deposition and filtration on contaminant concentration.
"CONTAMW allows the analysis of large buildings with hundreds of zones. You couldn't do this without a computer," said Andrew Persily, Ph.D., NIST Indoor Air Quality and Ventilation group leader. While CONTAMW has broad applications, according to Persily, its major non-research application is building smoke control system design.
Smoke, not flame, is the primary killer in a building fire. Smoke travels rapidly throughout a building and it's critical that escape routes, such as stairwells, are protected so that occupants can escape to safety.
One way to keep smoke out of a stairwell is to maintain the stairwell at a slightly higher pressure than the rest of the building. CONTAMW helps engineers design a building's smoke control system so that it ensures effective protection under a variety of wind and HVAC configurations.
Indoor air quality expert Terry Brennan, Camroden Associates (www.camroden.com) uses CONTAMW to evaluate building designs to identify and correct potential IAQ problems before construction. "I can look at the air flows throughout the building, including the mechanical flows, stack flows and wind-driven flows through ducts, walls, floors and around pipes, for different outdoor conditions. …