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Comparison of Measured and Predicted Tracer Gas Concentrations in a Townhouse



Steven J. Emmerich, Steven J. Nabinger, A Gupte, Cynthia H. Reed, L A. Wallace


To further validate the use of the multizone airflow and contaminant model, CONTAMW, experiments were performed in an occupied 3-story townhouse in Reston, VA. A tracer gas, sulfur hexaflouride (SF6), was manually injected within one room of the house and the concentration of SF6 was measured in each zone. This same process was then recreated in CONTAMW and the resulting predictions were statistically compared to the measured values.The base model of the house and the contaminant parameters were kept identical for each simulation. The location of the burst source of tracer gas the contaminant within the house was varied correspondingly to the zone in which the manual injection was performed. Data for ambient conditions including temperature and wind were also collected and accounted for in each simulation. The outdoor concentration of SF6 was assumed to be zero.A total of 11 experiments were conducted and simulated between May 2000 and June 2001. The tests involved injecting 1500 mL of SF6 in a single room of the house. In 4 of the 11 cases, the heating and air-conditioning system fan was operating. One test case was performed with an attic fan operating. SF6 was injected in the Recreation Room (basement level), the Kitchen/Dining Room (main level) and the Master Bedroom (upstairs level). Ambient conditions ranged from a low outdoor temperature of 5 C to a high of 29 C. Wind conditions ranged from calm to moderate with a high average wind speed of 4 m/s.A statistical comparison of measurements and predictions was performed per ASTM Guide D5157(ASTM 1991) for all cases. Comparisons were made for overall zone average concentrations and individual zone transient concentrations. The results for zone average concentrations were very good with many cases meeting most or all of the D5157 criteria. Several cases showed a poor to fair correlation between average measurements and predictions due to discrepancies with a single zone the main floor bathroom but excluding that zone resulted in these cases meeting or coming close to meeting the D5157 criteria.Comparisons of individual zone transient concentrations were mixed with many good to excellent cases but also numerous fair to poor. As expected, there were frequently large differences between measured and predicted peak concentrations. Also, the bathroom zone was a consistently difficult zone to predict accurately. Other zones had occasional poor comparisons between predictions and measurements but did not have any consistent discrepancies. The predicted SF6 concentration averaged over all zones and cases was within 10 % of the average measured concentration. Excluding the bathroom zone, the overall average predicted concentration (19.5 ppbv) was essentially identical to the overall average measured concentration (19.3 ppbv).
NIST Interagency/Internal Report (NISTIR) - 7035
Report Number


airflow modeling, building technology, computer simulation, infiltration, multizone, residential buildings, validation


Emmerich, S. , Nabinger, S. , Gupte, A. , Reed, C. and Wallace, L. (2003), Comparison of Measured and Predicted Tracer Gas Concentrations in a Townhouse, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed April 23, 2024)
Created August 1, 2003, Updated February 19, 2017