July 9, 2020
Global atmospheric carbon dioxide (CO2) concentration has been rising at an unprecedented rate since the first Industrial Revolution (the steam engine) in the late 18th century. CO2 is measured in parts per million (ppm), indicating how many particles of 1,000,000 particles of air are made up of CO2.
The highest measured CO2 concentration, by core drilling of ice, before the Industrial Revolution was approximately 300 ppm about 350,000 years ago. The first Industrial Revolution took place between 1760 through to roughly 1840 and historians can identify two further industrial revolutions since that point – the age of science and the digital revolution, both accelerating the rise of CO2. From then to now, global atmospheric CO2 concentration rose from approximately 280 ppm to over 400 ppm in 2020.
These levels of CO2 concentration are completely unprecedented and humans, as the predominant cause of this higher rate of increase, are still struggling to adapt and overcome.
CO2 makes up about 0.04% of the composition of outdoor air. In a classroom, a CO2 concentration of less than 1,000 ppm is considered good. This brings the total CO2 concentration to only 0.10% of typical classroom air.
So, why then are we so concerned with room CO2 concentration when it makes up so little of our indoor air? One could assume that increasing CO2 concentrations would reduce the capacity for room air, but a change in oxygen level of 0.06% has very little effect on the human brain.
Our understanding of the impact of CO2 is not new; the Bohr effect was first described by a Danish physiologist, Christian Bohr, in 1904. Bohr found that oxygen disassociation, which is the inhibition of the ability for haemoglobin to carry oxygen, was heightened by both an increasing blood- CO2 concentration and decreasing blood pH. The primary function of haemoglobin is to carry oxygen to the organs in our bodies. So, as blood-CO2 concentration increased the brain received a lower quantity of oxygen inhibiting its functionality.
The Bohr Effect strengthens with a reducing size of body. Therefore, a child is going to be more impacted by the room CO2 concentration than an adult. If we consider the increasing outdoor CO2 concentration, it stands to reason that we should be increasingly concerned about CO2 concentration in our classrooms. In Bohr’s day, however, the global atmospheric CO2 concentration was closer to 290 ppm, about 25% less than it is now.
While the original data for the impact of CO2 concentration on the brain dates to 1904, some more recent studies have been done by several reputable organisations. In 2016, Harvard University investigated the link between CO2 concentration and cognitive function in a study entitled, “Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: A Controlled Exposure Study of Green and Conventional Office Environments.”
Harvard University tested adults in several criteria, such as applied activity level, information usage, and strategy in rooms of varying CO2 concentrations. The rooms, labelled conventional, green, and green+ have CO2 concentration of 1,400, 900, and 500 ppm respectively. BB101 requires mechanically ventilated classrooms to be better than the “conventional” standard.
The results are stark; in all categories the performance of the groups is noticeably inhibited by the room CO2 concentration. Some of the factors here are incredibly important to one’s learning ability – basic activity level, applied activity level, focused activity level, information usage, and strategy, which are all very strongly affected. Interestingly, the effect is much more pronounced between 1,400 ppm and 900 ppm, than 900 ppm and 500 ppm, suggesting that there may be a turning point between 900 ppm and 1,400 ppm.
When considering these results, one should bear in mind that Bohr’s Effect is strengthened on smaller bodies, such that the results of Harvard’s study would be amplified on a younger occupancy.
Based on this evidence, a key performance indicator (KPI) for classrooms should be set below 1,000 ppm if we are to achieve the best performance in our schools.
The University of Surrey
In 2020, The University of Surrey produced a paper entitled, “Mitigating exposure to traffic pollution in and around schools.” The document sets out clear strategies to provide schools with simple action points aiming to reduce the exposure of children to air pollution in schools.
Their 10-point plan primarily involves passive measures of pollution mitigation including creating clean air zones around schools, using passive control systems (e.g. green barriers), careful planning when building schools, reducing vehicle usage and use of mechanical ventilation with air filtration. Most of these plans rely on participation from external parties and are therefore uncontrollable. M&E designers can, however, guarantee reductions in indoor pollutants and an appropriate room CO2 concentration by making use of filtered mechanical ventilation.
Where high ventilation rates have been adopted, UK schools have seen a noticeable improvement in classroom performance. A teacher from Reigate Grammar vowed to “never close the window” during exams after having reviewed the evidence from Harvard University. The same teacher carried out his own tests; by having the windows open they experienced classroom CO2 concentrations falling to approximately 400 ppm. However, with the windows shut the classroom CO2 concentration rose to as much as 2,000 ppm and noticeably inhibited the pupil’s concentration levels and performance. (https://schoolsweek.co.uk/school-hopes-fresh-air-will-help-clear-exam-minds/)
The impact of high CO2 concentrations could be considered more severe when one considers an exam scenario; perhaps 100-200 pupils in a large room with poor ventilation for up to three hours at a time. During that period, without sufficient ventilation, the room CO2 concentration could easily exceed 2,000 ppm. From Harvard University’s evidence, we know that this will have a detrimental effect on the pupil’s performance during some of the most critical times of school careers. If CO2 concentrations are properly managed – a KPI of below 1,000 ppm – then exam performance could be improved.
Intervention by teachers is critical if we are to succeed in improving our indoor learning environments. Whilst some ventilation systems do inform teachers of the room CO2 concentrations, they lack the fundamental understanding of the benefits of increased ventilation rates. Consequently, these devices are often taken for granted and ignored. One strategy to aid teachers could be a combination of demand controlled mechanical ventilation in tandem with the ability to open windows. In parallel, papers such as this could help educate teachers on the benefits of increased ventilation rates. If teachers understand the implications of poor indoor air quality, they can choose to improve the learning environment for their pupils.
Ventilation and mechanical equipment design in UK schools is driven by BB101: Guidelines on ventilation, indoor air quality and thermal comfort in schools. For ventilation in classrooms, BB101 requires that mechanical ventilation units meet a daily average CO2 concentration of 1,000 ppm. Natural or hybrid ventilation units operating in natural mode are permitted a daily average CO2 concentration of 1,500 ppm. Both can be exceeded by 500 ppm by no more than 20 consecutive minutes a day.
These figures pale when compared to our European counterparts. Whilst this list of not exhaustive, it does include some of the highest achieving countries in Europe. Finland, Norway, Denmark, Holland, Belgium and Germany all permit a maximum CO2 concentration in classrooms of 1,000 ppm, and France has reduced this limit to 900 ppm. Penalties may be given for exceeding these limits.
Therefore, European school children receive a better quality of education if we consider indoor CO2 concentration alone.
The daily average CO2 concentration enables ventilation units to perform poorly whilst occupancy is high, up to a limit of 1,500 ppm, and then to reduce the CO2 concentration when rooms are unoccupied. As such, BB101 does enable mechanically ventilated classrooms to poor poorly. For naturally ventilated classrooms, the limits are even less stringent and therefore pupils in schools with natural ventilation systems are at a consistent disadvantage to those with mechanically ventilation classrooms.
By working with mechanical ventilation, M&E engineers can choose to achieve better indoor environmental quality.
Having established that low CO2 concentration is essential for a good learning environment, the quality of the air being supplied into the room to replace extracted air must be considered. In a typical classroom, the volume of room air may need to be changed approximately 5 times per hour to achieve a daily average of 1,000 ppm of CO2. That means that the entire volume of room air every 12 minutes. This air must be brought in from outside.
But we know that the air outside our classrooms is heavily polluted. Consequently, the UK government has implemented a range of initiatives to combat emissions around our schools. However, there is evidence confirming that pollution levels around schools continue to be very high. Until we exclusively use “clean” energy sources, this problem will exist.
The table above shows the range of pollutant particulates that are present in the air. While some of these pollutants are not considered damaging, many of them are known to have a long-term impact on health. Poor air quality remains the largest environmental health risk in the UK and is said to be responsible for 4.2 million deaths per year. Children are among the most vulnerable to pollution’s harmful effects as their lungs are still developing, and arguably the least responsible.
Professor Paul Cosford, Director of Health Protection and Medical Director at Public Health England (PHE), said, “Now is our opportunity to create a clean air generation of children, by implementing interventions in a coordinated way. By making new developments clean by design we can create a better environment for everyone, especially our children.”
BB101 advocates the use of filtration in schools where pollution levels are considered unacceptable by The World Health Organisation (WHO) requiring a minimum of F7 filtration in areas considered “polluted.” F7 filtration must remove a minimum of 55% of particulates sized one micron and above.
Filtering air is the only practical method to clean air entering classrooms. Filtration can only be used with mechanical ventilation, so if good indoor air quality is required then mechanical ventilation must be used. Natural or hybrid ventilation systems do not filter air and are therefore unsuitable for use in areas of high pollution.
Whilst focusing on CO2 concentration may have an immediate effect on performance, there are other design factors that also influence children’s learning ability. The Danish Technical University (DTU) undertook a study in early 2020 of 92 pupils aged 10-12 years, who over four weeks answered a questionnaire and three different performance tests which measured their processing speed, concentration, logical reasoning and maths solving abilities.
They were tested in rooms where the lighting and room CO2 concentration were modified to create different learning environments. In this instance, the acoustics of the classrooms were already acceptable, but acoustics had previously been considered an essential variable to be managed in classrooms. In the UK, we use BB93: acoustic design of schools as a guideline for acoustics in classrooms.
The evidence showed that if you control the acoustics, light, and indoor air quality correctly you can easily achieve a 10% improvement in educational performance. That equates to an extra year of education over a period of ten years. In some classrooms, with lower achieving pupils, they even achieved a 20% improvement in performance.
By taking a holistic view of classroom environmental quality, we can achieve jumps in academic performance.
The room CO2 concentration is intrinsically linked to the room’s ventilation rate. To achieve a lower concentration at consistent occupancy levels, more air must be expelled and replaced in the room. To achieve the KPI of a room CO2 concentration of below 1,000 ppm, an increased ventilation rate will be required.
For concerned parents and teachers, room CO2 concentration can be measured using sensors. CO2 sensors can be purchased at low-cost and situated in classrooms where room CO2 concentration is of concern. These sensors are often equipped with data logging facilities such that data can be recorded over a period of days to give a more comprehensive view of indoor air quality.
Classroom ventilation units are typically equipped with integrated CO2 sensors that read the CO2 concentration of all air being extracted from the room. Using this data, fan speed and air change rate is modulated to guarantee a suitable CO2 concentration in teaching spaces.
Pollution levels can also be measured. Simple observation of the proximity of common pollution sources, such as vehicles, to school buildings can give a good indication of whether it is appropriate to supply unfiltered air into classrooms. Small and low-cost monitors are available for less than £40, giving a sensible idea of nitrous oxide and other particulate concentration in the locality, but they do not give indications of which particulates the air is composed of.
Some classroom ventilation units can also be equipped with air quality sensors that measure volatile organic compounds (VOCs) which are often present in furniture. VOCs tend to be released into the air when CO2 concentrations increase, creating a small chemical reaction. These chemicals are known to be damaging to children’s health, particularly if they have existing respiratory conditions, such as asthma. In fact, poor indoor air quality has often been correlated with increased school absence due to illness.
Protecting the health of our children is the top priority of all parents. Once they leave the home, they may be out of sight but never out of mind. It would make sense, therefore, that their learning environment should be as optimised for the maximum benefit of the pupil’s long-term health and academic performance.
To achieve this, it is necessary that we manage CO2 concentrations in classrooms such that they avoid negatively impacting children’s education. Pollution levels in classrooms must be actively managed, while a holistic view must be taken on indoor environmental conditions, managing not only the air quality but also the lighting and acoustics of the classroom. In doing so, we could see as much as a 20% improvement in school performance.
A school achieving a room CO concentration of below 1,000 ppm, the KPI set out here, should be considered to excellent indoor air quality.
It is not only M&E designers that need to take account of the detrimental effect some methodologies may have on their children, but also parents and teachers who strive so hard to improve educational performance for their children.