We have demand controlled ventilation in spaces with varying occupancy. The building is a YMCA. The controls contractor set the CO2 level to 1000ppm which is what is in the Sequence of Operations. The reviewer questioned the CO2 level for partial occupancy conditions. After a call and several emails with very long delays, we were given some cryptic guidance for calculating the CO2 setpoint in accordance with ASHRAE 62.1-2010 Appendix C. However, it does not give us a low end for PPM CO2. After completing the claculations, I have a few spaces that at 10% occupancy would have a CO2 setpoint of about 500 ppm. That seems unreasonable low. I have questioned the reviewer about a "low limit" for CO2 setpoint, but it has been two weeks and no response. Can someone give me guidance about what they will accept? Would 700 PPM be a reasonable CO2 setpoint? This has been dragging out for months now.
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otto
1 thumbs up
December 16, 2020 - 9:37 am
This is a new requirement to me. Appendix B of ASHRAE 62.1 lists upper thresholds for various compounds at different exposure lengths. As far as I know the thresholds do not change based on the number of people. I would put it on the LEED reviewer to provide information from ASHRAE or another professionsl society or even building codes showing the need for reduced concentration limits for reduced occupancy.
I am curious to know how the BAS would determine if a space is partial-occupied vs. unoccupied vs. occupied?
Fotis Kotsopoulos
December 16, 2020 - 10:03 am
800-1200ppm it's a reasonable range to work with.
Dave Hubka
Practice Leader - SustainabilityEUA
LEEDuser Expert
494 thumbs up
December 16, 2020 - 10:58 am
The monitoring requirement of naturally ventilated spaces include an option to monitor carbon dioxide concentration within each thermal zone. The option requires that project teams calculate the appropriate carbon dioxide setpoint(s) using the methods outlined within ASHRAE 62.1-2010, Appendix C.
it is not entirely clear from the original post if the spaces in question are mechanically ventilated or naturally ventilated.
If mechanically ventilated, project team needs to demonstrate system can supply outdoor air rates during the worst-case condition rather evaluate carbon dioxide levels.
My advice, complete (2) ventilation calculations. One with max occupancy and One with min occupancy. Then demonstrate that the outdoor air rate will fluctuate between the min / max rates of the calculators.
Hope this helps, Good Luck!
Nancy Henderson
Managing MemberArchEcology, LLC
83 thumbs up
December 16, 2020 - 5:19 pm
@ Otto - the reviewer said based on Appendix C, the required OA per person increases as the occupancy decreases. They sent some example calculations. Their example did not go lower than 700 ppm setpoint. Maybe that is a safe number.
The upper limits for CO2 concentration are based on steady state.