Outdoor air delivery monitoring | U.S. Green Building Council
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LEED O+M: Existing Buildings | v2 - LEED 2.0

Outdoor air delivery monitoring

EQc1 | Possible 1 point


Provide capacity for ventilation system monitoring to help sustain long-term occupant comfort and well-being.


Install permanent monitoring systems that provide feedback on ventilation system performance to ensure that ventilation systems maintain minimum ventilation rates.

Option A

For mechanical ventilation systems that predominantly serve densely occupied spaces (spaces with a design occupant density greater than or equal to 25 people per 1,000 square feet (40 square feet per person)), do the following:

  • Provide a CO2 sensor or sampling location for each densely occupied space, and compare with outdoor ambient CO2 concentrations.
  • Test and calibrate CO2 sensors to have an accuracy of no less than 75 ppm or 5% of the reading; whichever is greater. Sensors must be tested and calibrated at least once every five years or per manufacturers’ recommendation.
  • Monitor CO2 sensors by a system capable of and configured to trend CO2 concentrations on no more than 30 minute intervals.
  • Configure system capability to generate an alarm visible to a system operator and, if desired, to building occupants if the CO2 concentration in any zone rises more than 15% above that corresponding to the minimum outdoor air rate required by ASHRAE Standard 62 (see IEQ Prerequisite 1).
  • CO2 sensors may be used for demand-controlled ventilation provided the control strategy complies with ASHRAE Standard 62 (see IEQ Prerequisite 1), including maintaining the area-based component of the design ventilation rate.
Option B

For all other mechanical ventilation systems:

  • An outdoor airflow measurement device must be provided that is capable of measuring (and, if necessary, controlling) the minimum outdoor airflow rate at all expected system operating conditions within 15% of the design minimum outdoor air rate.
  • The outdoor airflow measurement device shall be monitored by a control system capable of and configured to trend outdoor airflow on no more that 15-minute intervals for a period of no less than six months.
  • The control system shall be capable and configured to generate an alarm visible to the system operator if the minimum outdoor air rate falls more than 15% below the design minimum rate.
Option C

For natural ventilation systems, provide the following:

  • CO2 sensors located in the breathing zone of every densely populated room.
  • CO2 sensors located in the breathing zone of every natural ventilation zone.
  • CO2 sensor(s) located outdoors.
  • CO2 sensors shall provide an audible or visual alarm to the occupants in the space and building management if CO2 conditions are greater than 530 parts per million above outdoor CO2 levels or 1,000 parts per million absolute. The alarm signal should indicate that ventilation adjustments (i.e. opening windows) are required in the affected space.
  • Operable windows areas must meet the requirements of ASHRAE 62.1-2004, section 5.1.
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