CO2 Sensors Make Buildings Safer, More Energy Efficient

The next time you step into a brand-new building, take a look at the wall. Next to the thermostat you might see another box with a CO2 sensor inside. That CO2 sensor is the end result of years of research into balancing indoor air quality and energy efficiency in building design.

Every home, school and office building requires a constant flow of fresh, conditioned air to make it comfortable for the people who live inside. In the past, this was not a problem. Most buildings were porous, i.e. outdoor air “leaked” into the building around windows and doors. Everyone has experienced a cold draft in an old building. 

While “leaky” buildings insure fresh air, they are also expensive to heat and cool. As energy prices began to rise, architects designed new buildings that minimized energy loss. For example, throughout the 1970’s many school and office buildings were designed with permanently sealed windows. While this saved energy, it had the unexpected consequence of sealing in mold, bacteria, and potentially harmful gases like radon, VOCs (volatile organic compounds), and carbon dioxide. Studies showed that high concentrations of these contaminants created health problems for occupants, and the term “sick building syndrome” was used to describe the new, sealed buildings. 

To combat “sick building syndrome” new HVAC (heating, ventilation, and air conditioning) systems were developed that fed a constant flow of fresh, outdoor air into buildings. The idea was that wasting energy to condition outdoor air was the price you had to pay to provide fresh air indoors. In some cases, these HVAC systems either provided non-stop fresh air, or in other cases they were set on timers that would open fresh air dampers when the building was occupied. 

In other words, the solution to providing fresh air was to open a window! 

In countries where energy is more expensive, an alternative method of providing fresh air was used. Instead of constantly providing fresh air, buildings used carbon dioxide sensors to “sense” when the building was occupied. When enough people enter a room, the CO2 level rises, and the HVAC system begins to pump in fresh air. When the people leave, the CO2 level drops, and the fresh air dampers are closed. 

This system of using CO2 to control HVAC systems is starting to catch on in the U.S. For example, many new commercial buildings are now designed to LEED (Leadership in Energy and Environmental Design) specifications. LEED provides a rating system for energy efficient building design. Included in LEED is a specification for using CO2 sensors to control fresh air circulation. 

At, we provide wall-mounted CO2 sensors used worldwide to control HVAC systems. So the next time you see a wall thermostat, look for a box beside it. It might say on the label.

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