Buying a CO2 meter? What should you look out for and which device suits your application?
At BaSystemen we have in recent months increasingly been asked about measuring equipment for CO2 / indoor climate. Although in the first months of the pandemic the focus was mainly on keeping your distance and wearing a face mask, the government has since added the advice to ventilate properly. In this article BaSystemen addresses the following questions:
- What is CO2?
- Effects of CO2 on people
- What do the Dutch regulations say about CO2?
- What is the correlation between CO2, virus particles and ventilation?
- Buying a CO2 meter, what should you look out for?
- The 3 most suitable devices
What is CO2?
CO2, or carbon dioxide, is a colourless and odourless gas that we humans breathe out. For those interested, this article explains clearly how our body absorbs oxygen into the blood and removes it again as CO2. We only breathe out small quantities, but over the course of a day this can build up steadily in an office space or classroom. In a room where nobody is present for a longer period, the CO2 concentration eventually becomes virtually the same as the outside air. The outside air contains a background concentration of CO2 which on average is around 400 ppm (parts per million). That depends on the region: in rural areas the concentration may be lower and in industrial areas somewhat higher. Over the years the background concentration of CO2 in the atmosphere has been rising due to industrialisation; in 1959 the concentration was still 316 ppm (source: KNMI)
Effects of CO2 on people
A well-known example is the meeting room effect. This is a situation in which a group of people sits in a meeting room, with windows/doors closed and no ventilation duct. Depending on the number of people and the size of the room, the CO2 level in the room will rise and can climb unnoticed from 400 ppm to 1500, 2000 ppm or more. At these levels you will notice that concentrating becomes more difficult and people start to yawn; opening a window works wonders at such a moment. In this case, buying a CO2 meter can help to monitor a healthy indoor climate.
| 400 ppm | Background concentration in the atmosphere |
| 400 – 1,000 | Usual concentration in buildings and spaces with good ventilation |
| 1000 – 2000 | Complaints of tiredness |
| 2000-5000 ppm | Headache, drowsiness, poor concentration, increased heart rate or nausea |
| 5,000 ppm | Dutch occupational exposure limit in the workplace (safety) |
| 40.000 ppm | Directly harmful because this high CO2 concentration displaces oxygen. |
| 60.000 ppm | Impairment of vision and hearing |
| 70.000 ppm | Death within 5 minutes (at 20.9% oxygen) |
(Source: Wisconsin Department of Health)
What do the Dutch regulations say about CO2?
- As stated above, the Dutch limit value is 5000 ppm (TWA – 8h). That means that on the Dutch shop floor the average CO2 value to which employees are exposed over an 8-hour working day may not exceed 5000 ppm. In practice this does not concern office spaces and schools, but the industrial sector where, for example, CO2 cooling systems are used and staff have to enter a technical ceiling void containing CO2 pipework. Another example is a chicken slaughterhouse where CO2 is administered in high concentrations to put chickens to sleep.
- Furthermore, the Dutch Building Decree 2012 (Article 7.23) states that a room used for primary education must have a carbon dioxide meter.
- All buildings, both offices and schools, have to comply with the Building Decree 2012. It states (section 3.6.) that existing buildings and new builds have to comply with the requirements set for air refreshment.
- Finally, many websites and documents mention that companies and schools must ventilate properly. The above requirements from the Building Decree are aimed at the technical aspects of the ventilation system. The RIVM advises using CO2 as an indicator of air quality and the degree of ventilation, working towards a value of 1200 ppm. This is not a value laid down in law in the Working Conditions Decree or the Building Decree, but comes from a study by the GGD in which the behaviour of the CO2 level in a room was compared with the amount of ventilation that is legally required under the aforementioned Building Decree. The results are shown in the table below:
- When we combine point 4 above with article 6.2. Air refreshment from the Working Conditions Decree, the circle is complete. Put simply, it describes that a workplace in a building may only be used if the building complies with the requirements given in the Building Decree 2012.
| Ventilation class | CO2 level, 98th percentile (indoor-outdoor) | CO2 level, 98th percentile (incl. background conc.)* |
| 0. Very good | <250 ppm | <650 ppm |
| I. Good | 250 – 400 ppm | 650 – 800 ppm |
| II. Moderate | 400 – 600 ppm | 800 – 1000 ppm |
| III. Insufficient | 600 – 1000 ppm | 1000 – 1400 ppm |
| IV. Poor | > 1000 ppm | > 1400 ppm |
Correlation between CO2, virus particles and ventilation?
The Dutch government and the National Institute for Public Health and the Environment have both published articles about ventilation and the connection with the coronavirus. The government has an article online called the coronavirus and ventilation in buildings. The piece written by the RIVM is called ventilation and COVID-19 and can be read here. In addition, the Ministry of Health, Welfare and Sport, GGD THOR and Techniek Nederland asked the RIVM to provide further clarification on the advice requested about airborne transmission of SARS-CoV-2 over longer distances and what consequences this has for systems that control the indoor climate.
The current guidelines for preventing the spread of SARS-CoV-2 are based on the assumption that person-to-person transmission of the virus mainly takes place directly within a distance of 1.5 m via droplet infection released when coughing and sneezing, or indirectly via contact with contaminated objects or surfaces. On the basis of current insights (message of 28 July 2020) the RIVM states that it is unclear whether airborne virus transmission plays a role in the spread of SARS-CoV-2. It has been demonstrated that in experimental settings the virus particles can remain infectious for several hours in the air droplets. In conclusion, there is at present still insufficient evidence as to whether the virus can be spread over longer distances, then actually remains infectious and can lead to infections. What is clear is that efficient air refreshment dilutes potentially infectious air particles, which reduces the chance of airborne transmission of virus particles.
The conclusion from the RIVM and the Dutch government clearly states that there are no new rules for ventilation in buildings. It is emphasised, however, that sufficient air refreshment (ventilation) is needed in buildings, with reference to the current rules for air refreshment named in the Building Decree and the applicable national guidelines (e.g. the Working Conditions Act). This reduces the spread of pathogens (such as the coronavirus) that cause respiratory infections. As an additional point because of the coronavirus, the following two points must be taken into account:
- Avoid an air flow from person to person. For example from a desk fan or a standing fan
- The use of recirculation in a room is not recommended (recirculation is also air displacement and not air refreshment)
- Air shared spaces such as a meeting room, for example during the break or after the meeting once everyone has left the room
Buying a CO2 meter, what should you look out for?
It is difficult to establish in figures whether a room is well ventilated or not. The first type of investigation that GGDs are likely to carry out is CO2 measurement. The CO2 concentration is a good indicator of other contaminants spread by people and a good indicator of ventilation in rooms where relatively many people are present. CO2 is easy to measure, but there is also a lot of equipment on the market that does not meet Dutch standards. That is why buying a CO2 meter is not so easy; when choosing a suitable and user-friendly meter there are a number of things you need to look out for:
- Type of sensor
- Resolution and measurement error
- Measuring range
- Calibration method
- Alarm capability
- Data logging and reading it out
Type of sensor
Choose an NDIR (infrared) CO₂ sensor. Here there is a choice between ‘single beam’ and ‘dual beam’. The big difference is that a single channel sensor is calibrated on the basis of an external reference, as is the case with a self-calibrating function based on measured background values or calibration with a known quantity of gas, while with a dual beam the sensor has an internal reference. In the long term a single beam is more economical.
Resolution and measurement error
Every measuring instrument and its sensor has a measurement error (the extent to which the result on the screen deviates from the actual value). For a CO2 meter with a measuring range up to 5000 ppm an acceptable measurement error is 50 ppm, and for a measuring range up to 10000 ppm 100 ppm is an acceptable measurement error. However, manufacturers sometimes manage to mislead you with the word resolution. This is the number of digits the instrument is able to display. Example.
A CO2 data logger has a measurement error of 5% of the measured value and a resolution of 1 ppm. Because of the high resolution of 1 ppm, the device can display 533 ppm. However, because of the measurement error of +/- 5% the actual value can vary up to 560 ppm. So it is actually a nice addition that the resolution is 1 ppm, but with a measurement error that virtually every CO2 sensor has, such a low resolution is of no added value. In fact this wrongly makes it appear as though the measuring instrument can measure very accurately. This is a point to be critical about when you intend to buy a CO2 meter.
Measuring range
The measuring range is mainly important to keep an eye on with a view to your application. In measuring equipment a distinction is often made here between safety and health. For health (i.e. a pleasant and healthy indoor climate) a measuring range between 0 and 5000 ppm is often acceptable and a measuring range up to 10000 ppm more than sufficient. If the measuring range does not allow higher readings, it is not a matter of looking at a different measuring instrument, but much better to spend money on solutions to reduce the CO2 concentration. For safety applications, equipment is often used that can measure 0 – 20000 ppm or even 0 – 50000 ppm. An exceptional measuring range is 0 – 100 vol% and is used for process measurements in the biogas world or emission measurements at companies.
Calibration method
Buying a CO2 meter involves a lot of things, including the calibration method. Ageing of the sensor can cause ‘drift’. This is a constant change in the measurement results, which can become ever greater over time. Calibration is therefore important in order to keep seeing correct measurement results. Common calibration principles for CO2 sensors are listed below:
- Calibration gas calibration – This is a manual calibration carried out by a product technician. It often consists of a zero calibration in which 99.99% nitrogen is applied to teach the measuring instrument that this is 0 ppm CO2, i.e. the zero point. Subsequently a fixed concentration of CO2 (for example 0.5% CO2) is applied to teach the instrument that this is 5000 ppm. The device is then clever enough itself to determine the remaining values in the measuring range by means of the calculated calibration line. A calibration gas calibration is a more advanced type of calibration which considerably increases the accuracy of the measuring equipment. The sensor is no longer dependent on the values in the surroundings or the outside air, but has values stored in its own memory that are based on exact gas concentrations. Buying a CO2 meter that uses this calibration principle is often more expensive in the long term because of the calibration costs of an external party.
- ABC calibration – This is a simple and cheaper calibration, which is carried out automatically. ABC stands for Automatic Baseline Correction and is carried out in the background. In general a sensor using this principle calibrates itself once every eight days, but this depends on the firmware settings in your CO2 meter. The ABC algorithm works by collecting measurement data over a period of 8 days and comparing the lowest measured values with the 400 ppm level (background value of outside air), from which the sensor understands whether the zero point needs to be adjusted. The theory behind this is that for indoor climate use, at some point during the day, at night or at the weekend a room is unoccupied and the CO2 level should return to 400 ppm, the same as outside air. By storing the lowest CO2 readings taken over time in the EEPROM memory (Electrically erasable programmable read-only memory), a small deviation from 400 ppm can be calculated and then added to or subtracted from the actual CO2 readings. By gradually applying small corrections again and again, the sensor keeps itself stable. The algorithm does not affect the linearity of the output signal. The advantage of this ABC algorithm is that it is a cheaper and simpler method. Thanks to the automatic calibration it requires little maintenance and relatively accurate values can be achieved. The danger lies in environments where work also takes place at night or at the weekend, in which case this principle cannot be used. If you have any questions about this, please feel free to contact one of our specialists.
Alarm capability
Buying a CO2 meter almost always comes with an option to raise an alarm when excessively high alarm values are reached. There is a difference here between a local alarm (beeping and flashing) and a discreet online alarm (for example by e-mail or text message). We see that in the safety sector a local alarm is often used, so that employees are immediately aware that the carbon dioxide concentrations are becoming dangerous. For indoor climate an e-mail is often convenient, or an LED indication (green, orange, red) as a signal for a teacher or office worker to open a window for a moment to air the room.
Data logging and reading it out
You can buy a CO2 meter with online functionality where the data is automatically saved and kept on the internet. You then receive a login name (e-mail address) and password and have an immediate overview of all measurement data from the equipment that is active in your organisation. Another possibility is that your equipment has no online functionality and the data is kept on the CO2 meter. This data can then be taken out of the device by connecting it to the computer with a USB cable and downloading the data manually. The last option is a CO2 meter that logs no measurement data at all and only displays current values.
Buying a CO2 meter – the 3 most popular CO2 meters
The KIMO HQ210 is a widely used measuring instrument for measuring the indoor climate, used by occupational hygienists and safety experts. It is a professional and versatile device that can be used for all kinds of applications and can be extended with a wide range of probes. It is common to walk around with this device, but it can also work on a tripod with mains power as a climate tree and be left in place for longer periods. The KIMO HQ210 has no online functionality and is calibrated with calibration gas.
Would you like to buy, rent or view this CO2 meter?
The IBS logger is an indoor climate logger with online functionality. The device is extremely suitable for use in company offices or schools for indoor climate measurements focused on CO2, temperature and humidity. The real-time values are shown on the screen, but the device can also give a local alarm by flashing. In addition to a local alarm, the IBS logger can send an e-mail when a limit value is exceeded. The device lasts for weeks after a charging cycle and sends its data automatically to the internet in the background. Would you like to buy, rent or view this CO2 meter?
The IBS logger is an indoor climate logger with online functionality. The device is extremely suitable for use in company offices or schools for indoor climate measurements focused on CO2, temperature and humidity. The real-time values are shown on the screen, but the device can also give a local alarm by flashing. In addition to a local alarm, the IBS logger can send an e-mail when a limit value is exceeded. The device lasts for weeks after a charging cycle and sends its data automatically to the internet in the background. Would you like to buy, rent or view this CO2 meter?
The AirZenZ-01 is our most widely used and cheapest solution for continuously monitoring the indoor climate in classrooms and office spaces. The device has sensors for CO2, temperature, relative humidity, light intensity and atmospheric pressure. Thanks to its online functionality via the LoRa-Wan network, the data costs are almost negligible and the user can receive notifications by e-mail when limit values are exceeded. The AirZenZ-01 also indicates this with an LED indication (green, orange, red). The alarm thresholds for this can be set by the user. Would you like to buy or rent this CO2 meter, or find out more? Then get in touch with our specialists.
