Space OK guideline Optimal Ventilation in the Classroom with the CO₂ meter: Analysis

The Knowledge Center for Space OK developed this guideline in February 2022 to support schools in achieving a healthy indoor climate through optimal ventilation and the use of CO₂ meters. Proper ventilation, which involves the continuous supply of fresh outdoor air and the removal of polluted indoor air, is one of the most important measures for a healthy indoor climate. Teachers play a crucial role in initiating ventilation measures in a timely manner. The CO₂ meter is a useful tool for this.

Part 1: CO₂ meters, signal values, and ventilation systems

The Function of the CO₂ meter

The meter measures the CO₂ level exhaled by students and teachers. The CO₂ concentration provides an initial indication of the degree of air exchange. The meter uses a display and a traffic light function to quickly indicate whether the CO₂ concentration (and thus the air exchange rate) is good, moderate, or insufficient. Based on this information, the teacher (or other attendees) can initiate ventilation or provide additional air/purge in a timely manner. The focus is not on the carbon dioxide CO₂ itself, but on the air exchange rate in the classroom.

Types of CO₂ Meters and Legal Requirements

Two main types of CO₂$ meters are used in schools.
Simple CO₂ meter (Building Decree): This has only a display and a traffic light function. This type was required in the 2012 Building Decree for new primary schools built from July 1, 2015.
Extended CO₂ meter (SUVIS): This type has a monitoring function that retains stored data for at least one year. This is required when using the SUVIS scheme (Specific Grant for Ventilation in Schools). The monitoring function ensures that the CO₂ concentration can be analyzed, which provides insight into the quality of the indoor climate.

Minimum Technical Requirements (Building Decree and SUVIS)

The requirements for the CO₂ meter are strict:

• The meter must operate continuously at the usual electrical mains voltage, with a temporary interruption not disrupting the set signal levels.
• The meter must calibrate itself automatically.
• Good CO₂ meters use a non-dispersive infrared (NDIR) gas sensor. The measuring range must be at least 300 to 5,000 ppm.
• The CO₂ concentration must be readable on a clear display, with the digits and letters in the display at least 8 mm high.
• The meter must warn with three signal levels:
  • CO₂ concentration less than 1,000 ppm.
  • CO₂ concentration between 1,001 and 1,400 ppm.
  • CO₂ concentration of 1,401 ppm and higher.
• The SUVIS regulation requires the use of a monitoring function that retains data for at least one year.

CO₂ Signal Values and Actions (Traffic Light Function)

The guidance links CO₂ concentrations to a traffic light function with clear actions:

CO₂ concentration, Indication, Required Action

800ppm, Good air quality (Green Zone), Leave air vents open continuously. If necessary, open one vent above 1.80m
800-1000ppm, Moderate air quality (Green Zone), Open additional vents above 1.80m. Turn up the heating when it's cold. 
1000-1400ppm, Inadequate air quality (Orange Zone), Open all casement windows above 1.80m. From 1200 ppm, also open casement/casement windows below 1.80 m
1400ppm, Poor air quality (Red Zone), Start (cross-ventilation)/ventilation (open windows and doors opposite each other, preferably 5-10 min during class changes or breaks). Report any exceedances to the school administration. 

The selection of the signal values depends on the school's ambition level (Fresh Schools Class A, B, or C).

Ventilation Systems and Action Strategy

The appropriate ventilation strategy depends on the type of ventilation system:
System A (Natural Supply and Exhaust): Uses air vents and windows. Action is primarily focused on opening windows.
System B (Mechanical supply, Natural exhaust): The teacher turns the ventilation on or to a higher setting.
System C (Natural supply, Mechanical exhaust): The teacher manually (or automatically) turns the mechanical exhaust on or to a higher setting.
System D (Mechanical supply and exhaust): The teacher turns the mechanical ventilation (if not automatically controlled) on or to a higher setting.
For systems with fully balanced and CO₂-controlled ventilation with sufficient capacity, additional measures are only necessary if the CO₂ value becomes too high.

Part 2: Installation, Quality, and an Integrated Approach

Tips for Selecting and Installing the Meter: Preferably choose a self-calibrating CO₂meter. Opt for 24/7 monitoring to monitor ventilation throughout the school. Installation: The meter should preferably be installed at a height of 1.2 to 1.5 meters in the living area. Prevent disturbance caused by opening windows and doors, sunlight, heating elements, or direct exhaled air (do not install within 70 cm of the person). A fixed power supply (mains voltage with interrupter protection) is recommended, although battery or accumulator power can also be chosen in certain cases.

Integrated Approach and Support: A good indoor environment goes beyond ventilation; it also includes temperature, humidity, acoustics, light, and cleaning. If ventilation with existing facilities is structurally inadequate, additional structural measures are necessary. Simpler methods should be followed first (instructions, operation, measurement, maintenance). The Ministry of Education, Culture and Science (OCW) has organized a package of measures, including the Optimal Ventilation Support Team, which actively supports schools with Quick Scans, instructions, and advice.

Jille Kuipers, Innovation Manager at LuxBalance, on the role of modern monitoring: "The Ruimte OK guidelines are crystal clear about the technical foundation: a self-calibrating NDIR sensor and the traffic light function are the minimum standards. But the most important insight is the need for 24/7 monitoring and data analysis, required by the SUVIS regulation. The RoomYou1 sensor, with its accurate NDIR sensor and data storage capability, enables schools to not only meet the minimum Building Decree requirements but also to ensure the ambition level (800 ppm target value). Moreover, a mobile monitor prevents disruption from direct breathing, a common problem with incorrectly installed fixed meters. It's not just about the red indicator; it's about reaching the green zone." By using a reliable CO₂ monitor and taking action according to the traffic light function, teachers and school administrators can take the right steps in time to create a healthy and productive indoor climate.

Reference:
Space OK. (2022, February). Guidelines for Optimal Ventilation in the Classroom with the CO₂ Meter. Space OK.