Uncertainty analysis of various CO2-Based tracer-gas methods for estimating seasonal ventilation rates in classrooms with different mechanical systems

Adel Kabirikopaei, Josephine Lau

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


Indoor air quality (IAQ) data of 220 classrooms in the Midwestern region of the US were measured during 2015–2017. During three seasons (fall, winter, and spring), indoor and outdoor CO2 concentrations of each classroom were measured under both occupied and unoccupied conditions. To calculate ventilation rates from the collected CO2 data, three main methods derived from the mass-balance equation were used: (1) steady-state; (2) decay rate; and (3) build-up. Since the uncertainty of the individual measurement parameter affects the accuracy or reliability of the calculated, an uncertainty analysis was performed for all three methods. The uncertainty of the estimated ventilation rates in relation to the volume of the classroom, indoor and outdoor CO2 levels, and estimated student CO2 emission rates were determined. The study shows that the steady-state method has the least uncertainty in ventilation rate calculations, while the decay and build-up methods had the lowest and highest values for ventilation rates, respectively. The results also show the estimated ventilation has a larger variance in single-zone systems than in multiple-zone systems. In field measurements, CO2 readings contribute to the largest portion of uncertainty for all three methods. Therefore, with CO2 as the tracer gas, improving the accuracy of CO2 measurement should receive the highest priority for study.

Original languageEnglish (US)
Article number107003
JournalBuilding and Environment
StatePublished - Jul 15 2020


  • Carbon dioxide (CO)
  • Classrooms
  • Occupied space
  • Uncertainty
  • Ventilation rate

ASJC Scopus subject areas

  • Environmental Engineering
  • Civil and Structural Engineering
  • Geography, Planning and Development
  • Building and Construction

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