Design Development

For mechanical ventilated spaces that are installing a BAS or BMS, the system should be capable of integrating with the CO₂ sensor and outdoor air flow monitors for immediate response with increased fresh air, such as demand-control ventilation.

All densely occupied spaces in mechanically ventilated buildings require the installation of at least one CO₂ sensor per space. Non-densely occupied spaces require an outdoor airflow (OA) monitoring device.

Mechanically Ventilated Buildings

All occupied spaces in naturally ventilated buildings require the installation of at least one CO₂ sensor. The number of CO₂ sensors depends on the project’s design and should be calculated by the mechanical engineer. Projects can use one CO₂ sensor for multiple spaces only if the project is ventilated by an approved “engineered natural ventilation system” according to ASHRAE 62.1-2007 requirements and if it does not require occupant intervention.

Naturally Ventilated Buildings

CO2 sensors can 1) measure the indoor concentrations of CO₂ and compare them against ASHRAE 62.1-2007 limits or, 2) measure the indoor concentrations of CO₂ and compare them against outdoor CO₂ concentrations. If you choose the second option, you will need to install outdoor CO₂ monitors as well.

The benefits of any monitoring device depend on the communication system, response and corrective action. Facility operators often find it very beneficial to automate the response by installing demand-control ventilation, which automatically regulates airflow as needed.

All monitoring devices must be able to trigger an alarm or automated response when actual measurements vary by 10% or more in either direction from the design set points.

The mechanical engineer and architect identify densely and non-densely occupied spaces as defined by LEED and determine the quantity and locations of all monitoring devices, and integrate them into the HVAC system. The mechanical engineer should verify that the monitors are designed to interface with a BMS system or trigger an audible or visual alarm if CO₂ concentrations or ventilation rates fall outside of the required range.

Use ASHRAE standard 62.1-2007 to determine outside air requirements.