Is CO2 a Good Proxy for Indoor Air Quality in School?

Session 7 Paper 3, CIBSE Technical Symposium, Liverpool John Moores University, Liverpool
11-12 April 2013

The increasing interest in indoor environmental quality of educational buildings has been underpinned by the rising incidence of asthma and respiratory disease among children, who spend a substantial amount of their lives on the school premises. The susceptibility of children to respiratory disease compared with adults has led to the formulation of regulatory frameworks for the provision of adequate Indoor Air Quality (IAQ), which have been framed around CO2 levels and ventilation rates. In the UK this included Building Bulletin 101 (BB101) and 2012 Output Specifications for School Buildings. Metabolic CO2 concentrations have been effectively used to estimate ventilation rates and infiltration in school buildings. Strong evidence links high CO2 concentrations and low ventilation rates to increased health symptoms and absenteeism and reduced academic performance in school classrooms. However, little evidence is available on the concentrations of the actual pollutants responsible for the health irritations under different ventilation conditions. This paper uses a sample of two Victorian primary schools in vicinity to central London area to evaluate the use of carbon dioxide as a surrogate for the provision of a healthy and comfortable indoor environment. Continuous sampling for 5 consecutive working days and passive sampling was used to determine indoor physical, chemical and microbial parameters in the winter season. The investigated schools were located in proximity and had similar physical characteristics and occupancy patterns. However, windows in one school were replaced and openings were kept shut for energy saving reasons. Monitoring survey revealed that the Victorian school that maintained original features complied with BB101 requirements. Increased airtightness of the altered building envelope together with poor facility management resulted to high CO2 concentrations above recommended guidelines. Overall, CO2 concentrations were a useful tool when carrying out IAQ investigations in schools. Increased ventilation rates were able to remove pollutants with indoor sources and prevented the built-up indoors of traffic related pollutants. However building orientation to the prevailing wind directions and outdoor pollution sources were more important for the prediction of indoor concentrations of outdoor generated pollutants.