CPD PROGRAMME | VENTILATION Sulphur dioxide Recommended over a 24-hour time period adversely affecting occupants. Levels of CO2 will primarily depend on the occupants. The Swegon review paper notes that a child aged seven to nine years old will produce half the amount of CO2 compared with a teenager this will make a significant difference when assessing the accumulating CO2 levels in the internal environment. A recent research review by Fisk,5 which considered research across the world, indicates time average CO2 values in surveyed classrooms ranged from 1,400ppm to 5,200ppm (in studies where 20 or more classrooms where investigated). This is illustrated, categorised by type of ventilation system, in Figure 2. Fisk notes that concentrations of CO2 do not appear to be systematically higher or lower in naturally ventilated classrooms relative to mechanically ventilated classrooms. His review reports that studies found average or median ventilation rates to be in the range of 3Ls-1 to 5Ls-1 per person, with one average as low as 1Ls-1 per person, and he concludes that there is a widespread failure to provide the minimum amount of ventilation specified in standards for classrooms. Adverse effects have been reported for elevated CO2 levels in classrooms, including decreased satisfaction with indoor air quality (IAQ),6 students experiencing greater fatigue and impaired attention span, and lower levels of focus among university students during lectures. The link between ventilation and achievement was observed in a study by Toyinbo et al,7 where preliminary analyses indicated statistically significant poorer results Figure 1: World Health Organization (WHO) outdoor air quality guidelines 2021 (and 2005) (Source: WHO14) in mathematics tests in schools where the ventilation rate was lower than 6Ls-1 per person. Toyinbo also links lower ventilation rates to more missed school days caused by respiratory infections. Lower ventilation rates may lead8 to increased asthmatic symptoms, and the risk of viral infections through the concentration of bioaerosols emitted from the occupants. Carrion-Matta9 noted research that indicated that high indoor concentrations of PM2.5 have been associated with asthma and cognitive impairment. The levels of particulates in the indoor air were determined as being strongly related to the outdoor air quality (rather than resulting from activities in the space itself) and were typically worse when ventilation rates were higher. This can pose a difficult compromise in locations with poor outdoor air quality and will increase the dependence on air-cleaning devices, such as particulate filters. In the US, Haverinen-Shaughnessy observed10 a link between ventilation rates and performance on standardised tests in maths and reading for nine to 10-year-olds, estimating that each 1Ls-1 per person increase in ventilation rate was associated with a mean increase of 0.5% in maths scores. A UK study11 by Clements-Croome et al indicates that pupils performance is increased by a very significant 15% in various tasks when ventilation rates in teaching spaces are increased from 0.71Ls-1 per person to 6-8Ls-1. Fisks review5 indicates similar improvements in performance with increased ventilation rates ranging from a few per cent up to as high as 15%. Recently, Wargocki et al12 reviewed data from published studies to derive systematic relationships between learning outcomes and air quality in classrooms, which predict that reducing CO2 concentration in classrooms (from the typically higher values as illustrated in Figure 2) to 900-1,000ppm would significantly improve performance in school tasks, concentration and daily attendance. In terms of ventilation rates, these results suggest that increasing ventilation rates from 2Ls-1 to 7.5Ls-1 per person will improve pupils performance in national tests by 5%, and childrens daily attendance by 1.5%. Notably, Wargocki concludes that the results provide a strong incentive for improving classroom air quality, and this might be assessed as part of cost-benefit analyses in systems design and operation. As classrooms are typically densely occupied spaces with a common rule of thumb being between 2m2 and 4m2 floor area per student TM57 notes that the ventilation rates required to maintain good IAQ are high in winter and even higher in summer. It is noted, in this pre-Covid publication, that the wider interest in IAQ of educational buildings is underpinned by the rising incidence of asthma and respiratory disease among children. In urban applications, the outdoor air may not be necessarily fresh (see panel, Fresh air?) but, practically, to maintain a good indoor environment, the school 50 December 2021 www.cibsejournal.com CIBSE Dec21 pp49-52 CPD 189.indd 50 26/11/2021 15:00