Selecting C[O.Sub.2]: Criteria for Outdoor Air Monitoring‪.‬

The operation of buildings is as, or is more important than, the original design in maintaining a healthy indoor environment and energy efficiency. A number of certification programs and standards specify the use of ventilation system performance monitoring. Monitoring is to be done either based on C[O.sub.2] concentrations in the occupied space or actual measurement of outdoor airflow, depending on the space design occupancy and ventilation type (mechanical or natural). For example, outdoor air delivery monitoring is a credit option for new construction, existing buildings and the core and shell LEED[R] programs from the U.S. Green Building Council. The current standards or program descriptions do not provide detailed guidance for determining what concentration of C[O.sub.2] should be considered the maximum concentration. The LEED-EB (for existing buildings) credit mentions C[O.sub.2] concentrations 15% above that expected to occur with a corresponding minimum outdoor airflow rate required by ANSI/ ASHRAE Standard 62.1-2007, Ventilation for Acceptable Indoor Air Quality, but does not list what the actual C[O.sub.2] concentrations are. LEED-NC, version 2.2, (new construction) offers a credit (EQ Credit 1) for monitoring of C[O.sub.2] concentrations in mechanically ventilated densely occupied ([greater than or equal to] 25 people per 1,000 [ft.sup.2] [100 [m.sup.2]]) spaces, and in all naturally ventilated spaces. Again, no specific maximum C[O.sub.2] concentrations are provided. The California Title 24 2008 Building Energy Efficiency Standards specifies a maximum C[O.sub.2] concentration of 600 ppm above ambient as a "one size fits all" criteria for spaces using demand ventilation controls. However, this only applies to California because it has its own ventilation standard, which is not based on Standard 62.1.