The advent of COVID-19 has made us all keenly aware of the critical role of high air quality, with good ventilation to mitigate the risk of infection. Yet the need to avoid this risk was recognized well before the pandemic arose, and will remain just as important even after it eventually recedes. Continuous ventilation control will always be one of any building’s Facilities Management tasks.

In England, for example, the Building Regulations 2010 Schedule 1 has a part F1(1) which requires that “There shall be adequate means of ventilation provided for people in the building.” The aim of this requirement is to protect the health of the building’s occupants by providing adequate ventilation. Without this, mould and internal air pollution may become hazardous to health and the risk of transmission of airborne infection is increased.

Yet, while minimizing infection risk is critical, air quality management is also essential for human comfort and productivity; CO₂ concentrations above 1000 parts per million (ppm)reduce productivity and can cause drowsiness. Above 2000 ppm, some people will start to suffer with headaches. However, a crowded classroom, for example, can have CO₂ levels up to 5000 ppm in adverse circumstances.

Using air quality monitoring to control ventilation and energy costs

In an ideal world, building operators could ensure high air quality simply through generous and sustained levels of ventilation, through opening plenty of windows and/or with air conditioning. However, both methods are energy-intensive, with heat lost through open windows, and electrical power needed to run the air conditioning. This creates extra, unwelcome energy costs, and increases the organization’s carbon footprint – an ever higher priority consideration for brand management. So it is important to continuously monitor air quality in a room or building, and use the air quality data to control the ventilation equipment appropriately and efficiently.

But how exactly can we monitor ‘air quality’? The answer is to measure CO₂ levels, as there is increasing evidence that these correlate strongly with airborne infection spread. People generate carbon dioxide as they exhale – and their exhalation also contains tiny liquid droplets (aerosols) which carry any virus particles present in their lungs. If a healthy person inhales these contaminated droplets, and if the number of virus particles they contain exceeds a minimum infectious dose, the disease is transmitted. While it is difficult to measure the viral load directly, monitoring CO₂ levels can mitigate the problem by preventing the build-up of reused air.

Whether in a public building or on public transport, the CO₂ concentration is influenced both by the number of people present, and their activity. Singing, loud speech, aerobic exercise or other aerosol generating activities will increase CO₂ levels in gymnasiums and other indoor sports venues, and dance studios. Also populations can quickly build up – and just as quickly disperse – in theatres, concert halls, pubs, nightclubs, or other places of public assembly.

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Elements of an effective CO₂ monitoring system

To cope with these different environments and rapidly-changing circumstances, CO₂ monitors must be accurate and responsive, while also being ultra-small in size and attractively priced. Suppliers are meeting these requirements by shifting to photoacoustic detector types, which perform better in all these respects than earlier devices based on non-dispersive infra-red (NDIR) technology.

Obtaining the best CO₂ monitoring results depends on how the monitors are deployed and used, as well as their technology. For example, it is best to place CO₂ monitors at head height and away from windows, doors, or air supply openings. Monitors that are positioned too close to people may give a misleadingly high reading due to the CO₂ in exhaled breath. They should therefore be positioned at least 500mm away from room occupants.

The amount of CO₂ in the air is measured in parts per million (ppm). If measurements in an occupied space seem very low (far below 400ppm) or very high (over 1500ppm), it is possible that the monitor is not in a suitable location. The monitor may need to be moved to another position within the space, to get a more accurate reading.

Instantaneous or ‘snapshot’ CO₂ readings can be misleading, so several measurements should be taken throughout the day. The frequency of measurements should be sufficient to ensure that changes in the use of the room or space throughout the day are represented in the readings. Levels of CO₂ may also vary throughout the year, as outdoor temperatures, and therefore behaviour relating to opening windows and doors, change.

As mentioned, photoacoustic detector technology facilitates smaller size among other detector benefits. This makes the detectors easier to integrate with microcontrollers and local network chips for communication with an onsite IoT gateway. The gateway consolidates data from all the sensors in an area – not just for CO₂, but also for related parameters such as temperature and humidity. In areas where light work is carried out the temperature range should be between 14ºC and 25ºC. Whereas the humidity should be in the range of 30% to 70%, unless there is a risk of static electricity. In this case, the humidity should not exceed 50%.

The IoT gateway sends the data via a 4G/LTE or possibly 5G link, in real time, to a Cloud based monitoring and control platform.

Software on the platform can analyse the data to understand trends, generate  actionable recommendations and deliver information and alerts to managers’ and technicians’ smart devices and PCs, wherever they are located. Data can also be stored on the cloud platform for more in-depth analysis of indoor air quality.

The need for total systems integration

In setting up a CO₂ monitoring and ventilation control system, it is vital to understand that success – in terms of efficacy, reliability and accuracy – depends on developing a complete systems solution in which all the components are not only of good quality, but also well installed and integrated.

In one survey, the Ministry of the Environment in Korea assessed the efficacy of 17 widely used air quality measuring devices by analyzing their accuracy and reliability. The result showed that only two devices provided accurate readings of indoor air quality. The other devices did not present accurate measurements of aerosol and total volatile organic compounds except carbon dioxide. In many applications, the CO₂ measurement may be sufficient, but the study shows how there can be room for improvement. In the report, the Ministry suggests that the low reliability of indoor air quality measurement values in most devices depended on many factors such as measurement methods, device structure, and data transmission.