Hello,
the credit language requires: "An alarm must indicate when the outdoor airflow value varies by 15% or more from the outdoor airflow setpoint." In the course of a coordination with the HVAC engineer the question occurred which setpoint should be used. A current one based on the current usage or a minimal setpoint for the project?
Planned is a VAV System with 100% outdoor air, where the airflow is regulated via CO2 sensors in the office/occupied spaces.
Additionally, the HVAC engineer asked if the via CO2 regulated airflow in a 100% outdoor air system isn´t already enough monitoring?
Maybe you can helo me out. Thanks in advance!
Christoph Keck
CES Clean Energy Solutions GmbH4 thumbs up
May 31, 2022 - 5:02 am
Hi,
do you mean the monitoring of the outdoor airflow rate? If so, this should be done with a direct measuring device. (Pressure Loss throughout the whole AHU for example)
Airflow monitoring in VAV systems | LEEDuser (buildinggreen.com)
The comments posted on the 13th of March will give you the details needed.
BR Chris
J Schütz
M.Sc.LCEE Life Cycle Engineering Experts GmbH
20 thumbs up
June 3, 2022 - 5:30 am
Hi,
thank you for your answer and the link to the helpfull comments regarding the monitoring implementation.
However, I still have the general question of how the setpoint is determined in a VAV system, since it actually changes with the current number of building occupants.
Dave Hubka
Practice Leader - SustainabilityEUA
LEEDuser Expert
429 thumbs up
June 3, 2022 - 7:41 am
My guess is if the setpoint changes based on occupant density, then the alarm setpoint should change right along with the outdoor airflow setpoints determined by the CO2 sensors.
I don't believe GBCI considers space located CO2 sensors with 100% outdoor air units to be outdoor airflow monitoring.
Maria Porter
Sustainability specialistSkanska Sweden
265 thumbs up
June 8, 2023 - 3:49 am
I get this question a lot in my projects, what set-point to use? We have 100 % outdoor air, and flow rates according to our code is often a lot higher than ASHRAE. Can we use minimum flow rates (when building is unoccupied, and VAV has not “kicked in”) as set-point? Why is this even a requirement for 100 % outside air systems with no recirculation? There are alarms already if the AHU would stop or somebody would alter the airflow…