Rating System

LEED O+M: Existing Buildings, LEED O+M: Existing Buildings

Rating System Version

v3 - LEED 2008, v3 - LEED 2009

Inquiry

The project building contains 40 AHUs which are each monitored and regulated based on CO2 differential rather than outdoor air introduction. In lieu of documenting a measurement of outdoor airflow at each AHU, the project team proposes to show compliance with the outdoor air ventilation rate required by ASHRAE 62.1-2007 by documenting the differential between the CO2 level in each AHU\'s return duct and the CO2 level in the outdoor environment. The correlation between the differential CO2 readings and the ventilation rate per person is described in Appendix C of the ASHRAE 62.1-2007 standard while Section 6.2.7 of ASHRAE 62.1-2007 supports the project team\'s use of CO2 differential to maintain an average ventilation rate per occupant in each zone. The project building utilizes a demand ventilation control sequence which was adapted to an existing outdoor air delivery system with motorized dampers that adjust the volume of outside air that is delivered to each zone. Damper adjustment is based on the differential between the CO2 levels in the return air duct and the CO2 levels in the outdoor environment. The control sequence utilizes a PID loop to help anticipate the volume of air required rather than try to catch up as the levels of CO2 increase on the floor.