white paper

CO2 Monitoring to Lower the Coronavirus Threat
Graham Martin, CEO and Chairman, EnOcean Alliance
There is increasing evidence that carbon dioxide levels in buildings correlate strongly withthe airborne spread of infection. Consequently, CO2 monitors could act as the “canary in thecoalmine” to mitigate the coronavirus threat.
Carbon dioxide is generated by the exhaled air of people who stay indoors. Each person in abuilding will exhale approximately eight liters of air per minute: air that has been in close
contact with the lung tissue(1). Alongside CO2 at a concentration around 40,000 parts permillion (ppm), the exhalation also contains tiny liquid droplets (aerosols) which, due to theirsize, can float in the air for a long time. These droplets will contain any virus particles
present in the lungs. Research shows a method to mitigate infection can be implemented
with CO2 monitors on site.
There is some consensus that sinking speeds of such aerosols are typically a few meters
per hour and a decrease in biological virus infection activity has a half-life of approximately
three hours in laboratory conditions(2)). This means that the room air remains polluted for along time. 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. Whilst
it is difficult to measure the viral load directly, energy harvesting wireless sensors are theideal way to monitor CO2 levels and hence prevent the build-up of reused air.

Measuring COVID transmission by proxyWith evidence like this increasingly pointing towards airborne transmission being a major
factor in the spread of the virus, the inference is that CO2 levels in rooms and other enclosed
spaces may be used as a proxy for COVID-19 transmission risk.
“Since the coronavirus is spread through the air, higher CO2 levels in a room likely mean
there is a higher chance of transmission if an infected person is inside”, leading aerosol
scientist Prof Shelly Miller writes in The Conversation. “Simply put, the more fresh, outside
air inside a building, the better. Bringing in this air dilutes any contaminant in a building,whether a virus or something else and reduces the exposure of anyone inside.”A 2019 study on a tuberculosis outbreak at Taipei University, Taiwan, provides detailed
evidence. Many of the rooms were poorly ventilated and reached CO2 levels above 3,000
ppm. When engineers brought levels down to under 600 ppm the outbreak stopped.

EnOcean Alliance Whitepaper – CO2 Monitoring to Lower Coronavirus Threatwhite paper
What level is safe?
Elsewhere, Prof John Wenger, director of the Centre for Research into Atmospheric
Chemistry in UCC suggests a target of 1,000 ppm if CO2 is being used as a proxy for
COVID-19 in classrooms, and argues that room level transmission is “the key. It’s in the air,and it can fill a room. The amount of the virus in the air can accumulate, and we getincreased exposure. If you’re indoors, in a poorly ventilated room for a long time, then you’reat quite a high risk even if you’re distanced, because the air moves around.”Indoor CO2 measurements using easy and low-cost to install sensors hold promise for themass monitoring of indoor aerosol transmission risk for Covid-19 and other respiratorydiseases. Different CO2 level targets should be set based on the environment and activity
type since infection risk level has been shown to vary by a factor of 100 or more dependingon the situation and activity type. Factors such as the number of infected people in a region
and measures such as mask-wearing or air filtration may reduce the presence of theairborne virus without reducing CO2 levels. Certain activities increase virus emission far
more than CO2 levels, such as talking, singing and shouting. Both CO2 and the virus are
diluted by ventilation with outdoor air. They are not, however, removed by recirculating theair, for example through heat exchangers.

The air that you breathe
If we are in a room with several people, the measurement of the CO2 concentration provides
a measure of what percentage of the air we inhale which consists of air that has alreadybeen exhaled by other people. The mass balance shows that a measured CO2 concentrationof approx. 1200 ppm means that almost 2% of the air in the room has already had lungcontact at least once. At this level, every 50th breath that a person takes in this room
consists of air that has already been exhaled. The resulting specific corona infection risk ismore complex to quantify, as it depends on various factors that are currently still being
intensively researched.(1) Notwithstanding these caveats, it is clear that CO2 measurement
offers a cost-effective solution for classifying the current risk from potentially infectious
aerosols.

Strategies to reduce infection risk
Putting the research into practice, the Federal Environment Agency has drawn up general
guidelines for health assessment of carbon dioxide in indoor air, which includes advice
regarding SARS-CoV-2 – advice that is also relevant to COVID-19. Accordingly, aconcentration of <1000 ppm is hygienically harmless. The guideline classifies aconcentration between 1000 and 2000 ppm as questionable and anything above it asunacceptable. CO2 is also an important indicator in the DGHK (Deutsche Gesellschaft für
das hochbegabte Kind - German society for gifted children) statement on prevention inschools.
Similarly, the UBA (Umweltbundesamt - German Environment Agency) ventilation working
group recommends the use of CO2 traffic lights for this purpose. The DGVU (Unfallkasse)goes even further and advocates a target value of 700 ppm in classrooms in times ofEnOcean Alliance Whitepaper – CO2 Monitoring to Lower Coronavirus Threatwhite paper
epidemic. The latest findings are summarized in the UBA guide "Ventilation in schools"(15.10.20), which was created for the KMK (Kultusminister der Länder in der Bundesrepublik
Deutschland).
Ventilation means not only air exchange but also heat loss in winter. A sustainable strategy
should also take this effect into account. Where there is no modern air-conditioning
technology with a heat exchanger, only monitoring of the CO2 and demand-oriented orregular manual cross-ventilation helps. REHVA, the Federation of European Heating,
Ventilation and Air Conditioning Associations has called for the installation in schoolclassrooms of CO2 monitors with traffic-light indicators, “at least in schools where ventilation
depends on opening windows and/ or grids”.

CO2 sensor implementation
To follow these strategies, CO2 monitoring devices need to be dependable, and easy toplace where they are needed. Ideally, they need to be connected, for example, to trigger
alarms when CO2 concentration goes above “traffic light” thresholds, even to send alarms tobuilding management networks, or to smartphones via wireless networks. Wireless, batteryfree sensors represent the ideal solution. Simple to fit and easy to maintain, such sensors
utilize energy harvesting technology to draw energy from their surroundings – for example
from motion, light, or temperature differences. Rapidly deployed, without the need for special
installation or wiring, such solutions enable continuous monitoring of carbon dioxide
concentration in the ambient air.

Dashboard for continuous monitoring of carbon dioxide concentration in the ambient air (source: EnOceanGmbH)

By sending measured values to a receiver or gateway for further processing, alarms can betriggered, and appropriate action initiated. For example, it is possible to start a room
ventilation system to reduce the CO2 concentration. What is more, a wide range of theseCO2 sensors works within the ecosystem of standards like the EnOcean Alliance. Thismeans that they can easily combine with other devices, such as room occupancy sensors
and access control, that are integral to COVID-19 measures.

www.enocean-alliance.org

EnOcean Alliance Whitepaper – CO2 Monitoring to Lower Coronavirus Threatwhite paper
Acknowledgments(1) COVID-19 Prävention: CO2-Messung und bedarfsorientierte Lüftung https://www.umwelt-campus.de/forschung/projekte/iot-werkstatt/ideen-zur-corona-krise(2) Modeling aerosol transport and virus exposure with numerical simulations in relation toSARS-CoV-2 transmission by inhalation indoors https://www.sciencedirect.com/science/article/pii/S0925753520302630#b0125

EnOcean Alliance Whitepaper – CO2 Monitoring to Lower Coronavirus Threat