Belgian Practical Guide to CO₂ Meters: Analysis for Publicly Accessible Spaces
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This Practical Guide was prepared by the Belgian Federal Public Service for Public Health and aims to support operators of enclosed, publicly accessible spaces in the selection, installation, use, and maintenance of CO₂ meters. This is a fundamental element of the Belgian strategy to protect the public against the risk of infection due to poor indoor air quality, as stipulated in the law of November 6, 2022.
Part 1: Selection and Technical Requirements of the CO₂ Meter
Why a CO₂ meter?
CO₂ is an interesting indicator of indoor air quality because its concentration directly correlates with the number of people and activity in the space. The higher the CO₂ concentration, the higher the concentration of aerosols (microdroplets from respiration) that can contain microorganisms, bacteria, and viruses. This increases the risk of infection. In public spaces where the CO₂ concentration exceeds the threshold of 900 ppm, efficient ventilation and air purification systems are strongly recommended.
Sensor Type and Accuracy
Belgian legislation and this guide impose strict requirements on the equipment:
1. Sensor Type: The sensor must directly measure the CO₂ concentration. The generally recommended type is the NDIR (non-dispersive infrared) CO₂ meter. Sensors that measure CO₂ "equivalent" or CO₂ indirectly should not be selected.
2. Measurement Range: Choose a device with a measurement range of at least 2000 ppm, and preferably 5000 ppm. The higher range is useful when using air purification systems, as these purify the air without removing the CO₂ present. 3. Accuracy: The maximum measurement error may not exceed 10% of the measurement (calculated on a range up to 2000 ppm). For example, with a measured value of 900 ppm, the actual value should be between 810 ppm and 990 ppm.
Calibration and Maintenance
Drift can occur due to aging, which affects accuracy. Regular calibration (comparison with outside air) is essential.
* Recommended types: "Dual beam" or "ABC Logic" sensors with automatic calibration are preferred. A sensor that can be manually calibrated with outside air is also a solution.
* Discouraged types: Sensors that require regular external calibration by the manufacturer or a laboratory are not recommended due to the cost and the risk of infrequent calibration.
* Inspection: Annual inspection using a portable reference sensor is recommended. If the difference exceeds 200 ppm, the device should be checked or replaced.
Information Type
CO₂ meters are classified according to the way they provide information:
1. On-Screen Display: Direct display on a screen is useful for immediate measurements and informing attendees.
2. Data Logging: Devices that store measurements locally or remotely (via an app or server) are very useful. This allows for analysis of CO₂ trends over time, which helps direct ventilation interventions and ensure compliance with guidelines (similar to systems in American schools).
3. Color Indicator or Alarm: A green, orange, or red LED indicator, an audible alarm, or a smartphone message informs users immediately when a threshold value is exceeded. Users must be able to set the threshold values themselves.
Fixed or Portable
This guide only applies to portable and transportable CO₂ meters (whether fixed to a wall or table). These devices are flexible. Battery-powered devices are easy to install but require battery replacement or charging; mains-powered devices are more reliable in continuous operation but less flexible.
Part 2: Installation and Practical Use
Device Placement
The CO₂ concentration in a room can vary due to partitions or open windows. Therefore, multiple measurements are required in larger rooms (> 50 m^2) or rooms with open windows.
The sensor must:
* Be placed in the occupied part of the room.
* Not next to an open door or window, or near the air intake of the ventilation system.
* Not near people. There must be a distance of at least 1.5 m from people.
* Be placed in the location indicated as the least favorable in the risk assessment (for example, at the back of a poorly ventilated restaurant or on a balcony in a theater).
Communication of the Values
Under the law of November 6, 2022, the operator must be able to inform visitors of the expected air quality. The measured CO₂ values can be communicated in various ways:
On-site: Via a screen or QR code. The reported readings must not be older than 5 minutes.
Online: Via a website or application. The readings must be updated no more than every 15 minutes and cover a period of at least 3 days.
Special case: Measuring in Exhaust Ducts: In spaces with exhaust ducts, it is possible to measure the air quality directly in the exhaust duct (requires specific duct meters). For multiple ducts, a flow-weighted average must be calculated. An alternative option is to place the meter in the exhaust duct located in the room with the poorest air quality and use that value for the entire space.
Use and Preliminary Tests
Preliminary Test: Place the device outdoors or near an open window. The CO₂ concentration should be between 400 ppm and 500 ppm. If the device measures too high or too low, it must be calibrated or serviced.
When to Measure: Continuous measurement or a series of random measurements with intervals of no more than 5 to 15 minutes is required. When using random measurements, it is recommended to measure at the end of the maximum occupancy period (the most critical situation).
Jille Kuipers, Innovation Manager at LuxBalance, on flexibility and measurement: "The Belgian guide sets high standards for the technical reliability of the CO₂ meter. The emphasis on NDIR sensors and the 10% accuracy limit is crucial. The most practical insight is the requirement to maintain a distance of 1.5 meters from people and ventilation openings. This strongly argues for flexible, portable meters, as fixed installations often cannot guarantee this requirement. The Room You 1 sensor is an ideal match because it is a portable NDIR sensor with data storage, and is also equipped with a bonus feature: the measurement of other indicators. This gives operators a more complete picture of indoor air quality, as required in the checklist."
Reference:
Federal Department of Public Health, Food Chain Safety and Environment (2024). Practical guide for the selection, installation, use, and maintenance of air quality meters (Version 1). Belgium.