Siemens HVAC Products  Indoor Air Quality a schools

A guide to Indoor Air Quality

By: Drew Knobloch, Sensors Product Manager, Siemens Smart Infrastructure USA 

We all know how important indoor air quality is, especially after experiencing the COVID-19 pandemic. But how do you measure something you can’t see? The answer is simple – sensors.


Creating optimum indoor air quality has many factors to consider including air circulation, inside and outside temperatures, humidity, CO2 levels, volatile organic compounds (VOC), and fine dust (PM2.5) particulate levels. At the same time, it can be challenging to find the right balance to improve indoor air quality while achieving energy efficiency and sustainability goals. 


CO2 Control – Improve productivity

CO2 is a colorless, odorless gas and a normal byproduct of cell function that is removed from the body in exhaled air. Indoor CO2 concentrations are not typically hazardous (<5000ppm), however, exposure to levels above 1000 ppm can lead to decreased energy and performance. The best way to ensure healthy CO2 levels is to implement an efficient Demand Control Ventilation system, bringing in sufficient heated and cooled outdoor air to dilute high concentrations of CO2 indoors.


What should typical CO2 levels be? Here’s a breakdown of the ASHRAE 62.1 standards for specific environments:

  • Typical recommended maximum CO2 levels are 1000 PPM for schools and 800 PPM for offices
  • Indoor CO2 levels should not exceed outdoor levels by more than 600 PPM
  • If outdoor CO2 is not being measured, assume 350-400 PPM for most locations


Volatile Organic Compounds (VOC) Control – Address offensive odors 
VOCs are man-made chemicals used in nearly every manufacturing process. They can live in furniture, paint, carpet, and even cleaning materials. The most common VOCs found in indoor air are ethylene glycol, formaldehyde, methylene chloride, toluene and xylene. Sound scary? It can be! When VOC levels are too high it can create an unpleasant environment even when CO2 levels are acceptable. Not to worry, though, as there are CO2 and VOC combination sensors that measure both to ensure the healthiest indoor air for your environment. 


Fine Dust Control – Reduce risk of lung diseases and other health issues

Fine dust, also known as particulate matter, is small particles (smaller than a grain of salt) that are suspended in the air. Most particulate matter is created outdoors, but it can also be created indoors.

Humidity Control – Limit spread of colds, flu, and other viruses

Relative humidity plays a key part in reducing the spread of colds, flu, and other viruses. In fact, studies have shown that there are 70% fewer colds and flu when humidity is controlled to 40%-60% RH. Here are the suggested recommendations:

  • ASHRAE recommends RH levels kept below 65%
  • US EPA suggests RH levels between 30% and 60% to reduce mold growth
  • RH levels between 40% and 60% reduce mold growth and may significantly reduce virus transmission1

Do your part in keeping your building and occupants safe. Monitoring CO2 levels, VOCs, particulate matter and humidity can help improve health and productivity while also ensuring your HVAC system is operating efficiently. For a more in-depth review of how any of these sensors work, watch our webinar.


While sensors help to address air quality issues and better manage them, connecting these sensors and other building automation systems into an open building automation software platform can provide better insight into the overall health of buildings.

American Society of Microbiology