CO2 sensors in return air duct instead of within the room

Ian, CO2 sensors for densely occupied spaces must be within the vertical breathing zone, which is 3-6 feet above the finished floor. In the referenced LEED Interpretation, the project is a Core and Shell project that is a) not required to provide CO2 sensors for densely occupied spaces, and b) is installing an EMS system that allows for future tenants to connect CO2 sensors installed in densely occupied spaces (which is a requirement for LEED-CS projects). A LEED-NC project has different requirements, which is likely why it seems as though USGBC has "allowed" this approach. Measuring the CO2 levels within the return air duct may not be as accurate as measuring the air within the vertical breathing zone, and therefore, locating CO2 sensors in the return air duct within densely occupied spaces is not a valid strategy for EQc1 for LEED-NC projects. Hope this helps.