Carbon Dioxide or CO2 is a greenhouse gas that is natural and harmless in small quantities, but as levels rise it can affect productivity and cognitive ability. CO2 is produced indoors by the air we exhale. CO2 levels rise indoors when there is less ventilation.

The OSHA Permissible Exposure Level (PEL) of CO2 is 5000ppm. The industry has developed detailed standardswhich carefully document how to handle the CO2 that we exhale. What should be the acceptable level of CO2 is a controversy. Both the CDC and ASHRAE agree that long-term CO2 levels should be no more than 700ppm above ambient (outside) which is commonly about 1100ppm. Education professionals at the state and local levels have found that CO2 is so closely coupled to learning that they have developed their own guidelines. As the science has progressed it’s becoming clear that cognitive effects can be detected at levels as low as 600ppm.

Ventilation is now understood to be a critical factor in the transmission of COVID and other airborne diseases. Since CO2 concentration is the net result of occupancy and ventilation, the use of CO2 as proxy to mitigate transmission is coming into focus.

Various industry groups such as LEED and USGBC have recognized the basic principle that “the installation of CO2 monitors provides feedback on ventilation performance so that adjustments to the amount of fresh air can be regulated.” Timely and accurate measurement of CO2 is the foundation of current and future regulatory compliance.

Design and construction techniques have improved energy efficiency by providing a reliable and controllable barrier between outside and outside air, resulting in a tradeoff between energy efficiency and air quality. When the amount of outside air is controlled the level of CO2 increases when ventilation does not increase at the same rate.

Increase the amount of outside air.

The most accurate way of sensing CO2 currently available is an NDIR (Non-Dispersive Infrared) sensor. This type of sensor detects the decrease in transmitted infrared light in proportion to gas concentration. The signals developed by this technique are very small and accuracy, particularly at low concentrations, requires a high degree of quality control. Accuracy and calibration are built into the WellStat devices, including the ability to periodically and optimally recalibrate this sensor in the field.