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If my project is using air handlers that supply 100% outside air at a constant volume, do I still need to install an airflow monitoring device?

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NC-2009 IEQc1:Outdoor Air Delivery Monitoring

CO2 sensors

We are working on an office project. The typical floor will be a completely open space, with workstations and meeting spaces (not enclosed). This will not be a densely occupied space. The design team proposes to install 4 CO2 sensors through the space (approx. 1.400m2 of net area) to regulate the outdoor air supply of the AHU based on CO2 levels. This approach is choosen because outdoor air calculations are based on a high occupancy rate, but it is not sure if this occupancy will be achieved or will change during the building lifetime. Would this approach meet credit requierements?

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Tue, 09/22/2015 - 14:04

Is the building naturally, or mechanically ventilated?

Tue, 09/22/2015 - 14:24

Mechanically ventilated

Tue, 09/22/2015 - 14:30

Great. In that case, you will only need to measure the airflow at the unit level in order to monitor the status of the OA flow and provide an alarm if it is outside of the limits. I recommend that you provide a narrative and include your reasoning behind the design supply of OA as well as the CO2 sensor control. The sensors will not be necessary for the credit, but they will probably wonder why they are there if you don't tell them ahead of time. Your design approach sounds very good.

Tue, 09/22/2015 - 16:31

Thank you Andrew. The CO2 sensors alone would not be enough to comply with the credit? If not, if we use 100% OA at unit level can we just monitor the operation of the fan?

Tue, 09/22/2015 - 17:28

If you want to consider the spaces as densely occupied, and the unit supplies less than 20% of its air to non-densely occupied spaces, then this approach will satisfy the credit. If you keep the spaces as non-dense, you will need direct flow measurement. As for the fan status, that applies only to a constant volume dedicated OA unit. If you plan to vary the OA percentage, you cannot use that method. Based on our control description, I assumed that you were monitoring the flow anyway. That way, when CO2 levels are satisfied, you can set the flow to a minimum pressurization level.

Wed, 09/23/2015 - 14:46

Thank you Andrew for your response

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