I have a 100% OA ERU that operates constantly on an occupancy schedule. There is no Outdoor airflow monitoring device on the unit and no CO2 sensors for the densely occupied spaces. Although as per ASHRAE 90.1-2007 6.4.3.9 Exception a. we don't need DCV due to energy recovery hence no CO2 sensors required.
Also, since this is a 100% OA system, the unit capacity is based on a constant airflow, meaning it will provide a minimum airflow based on the occupancy schedule input at the BAS, and the BAS will generate an alarm when the conditions vary from design value.
My question is - How am I supposed to fill the form when it doesn't give me an option to complete the form without checking the CO2 sensor and OA measuring device boxes?
Andrew Mitchell, P.E.
PrincipalMitchell Gulledge Engineering, Inc.
LEEDuser Expert
126 thumbs up
May 21, 2018 - 11:20 pm
There is a CIR that allows you to monitor unit status for constant volume systems in order to relive the AFM requirement.
As for the CO2 sensors, this is a USGBC requirement. They are not simply enforcing an ASHRAE requirement or requiring DCV. They just want to have the monitoring in densely occupied spaces. If you are not providing them, you do not qualify for the credit.
Nishank Shah
LEED Green AssociatePeter Basso Associates
May 22, 2018 - 9:11 am
Thanks for the reply, Andrew. Would you happen to know the CIR ID# for constant volume systems.
Also, I had a follow up question about CO2 sensors, the reason USGBC requires CO2 sensors as you pointed out is for monitoring. In our case, the ERU already has internal 7 days scheduling doesn't that account for monitoring in densely occupied spaces? OR if I'm understanding it correctly, as per USGBC, presence of CO2 sensors in densely occupied spaces is just a requirement and has nothing to do with the systems ability to schedule occupancy at the unit.
Andrew Mitchell, P.E.
PrincipalMitchell Gulledge Engineering, Inc.
LEEDuser Expert
126 thumbs up
May 22, 2018 - 10:59 am
Sorry, I do not have time to look up the CIR# right now. You can search the library and it should be easy to find.
You are correct. They do not require the CO2 sensors to control anything, just to provide an alarm if the level exceeds design.
Nishank Shah
LEED Green AssociatePeter Basso Associates
May 22, 2018 - 11:14 am
Appreciate your help. Have a nice day.