General [2]

Today, CO₂ is one of the most important indicators for evaluating the air quality in office and residential buildings. Since humans produce CO₂ by breathing and release it into the air, the CO₂ content in occupied, unventilated rooms increases rapidly. With increasing CO₂ concentration, room users experience odorous complaints and, with significantly increased CO₂ concentration, even health problems (concentration disorders, headaches, dizziness, etc.).

Thresholds

• In Switzerland, the Swiss Accident Insurance Institution is generally responsible for health-related limit values at the workplace [1].
• The SUVA publishes an annual report entitled “Occupational Exposure Limits”, which also includes the maximum workplace concentration values (MAK values).
• These are limit values that are intended to ensure health protection but NOT comfort: While the SUVA sets 5’000 ppm (parts per million) as MAK value for carbon dioxide, the guideline to the regulation 3 of the labor law states: “Good indoor air is given if the total concentration of 1’000 ppm CO₂ is not exceeded over the period of use of the room.
• In standard SIA 382/1 [3, Table 8], the Swiss Association of Engineers and Architects specifies a classification of indoor air quality. Residential and office spaces fall into category 3, for which CO₂ levels between 1’000 and 1’400 ppm are prescribed.
• The Swiss Air and Water Hygiene Association recommends values between 800 - 1’200 ppm for a good indoor climate, with the optimum at 1’000 ppm and a maximum value of 1’400 ppm [4]. These values are the default in the application.

CO₂ Sensor self calibration

• Most CO₂ sensors have a self-correcting ABC (Automatic Baseline Correction) algorithm.
• It is assumed that the sensor reaches the fresh air value of approx. 400 ppm CO₂ at least once in x days (sensor specific) by window- or mechanical ventilation.
• This algorithm constantly tracks the lowest measured value of the sensor over the last x days and slowly corrects the unavoidable long-term drift.

References

[1] SUVA: Grenzwerte am Arbeitsplatz
[2] http://www.nachhaltigebueros.ch/node/119 [3]SIA Schweizerischer Ingenieur- und Architektenverein (2014). Lüftungs- und Klimaanlagen - Allgemeine Grundlagen und Anforderungen. (SN, SIA 382/1). [4] Schweizerischer Verein Luft- und Wasserhygiene (2019). Messgerate_fur_Raumluft.pdf - Das ist gutes Raumklima. Retrieved August 31, 2020, from https://www.svlw.ch/