Demand-Controlled Ventilation

Redy Truccolo

Engineer

Greenwich Srl

LEEDuser Basic Member

26 thumbs up

June 30, 2011

Hi, in my proposed HVAC system I want to use a demand-controlled outdoor air ventilation (with motorized dampers controlled by CO2 detectors). So I will use an appropriate schedule (based on the occupancy) for this system. The ASHRAE 90.1 App. G Table 3.1 Section 4 seems to say that I've to use the same HVAC schedules for Proposed and Baseline systems. Should I have to use identical schedules for proposed and baseline? I'm asking this because if I do this way I will not have any energetical improvement due to the different outdoor air regulation. Thank you very much for your help. Regards

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Fri, 07/01/2011 - 13:12

Yes the schedules in the proposed and baseline must be the same. Some software models DCV directly without having to manipulate schedules to show savings. If your software does not, you will have to follow the exceptional calcualtion method to claim savings.

Redy Truccolo

Engineer

Greenwich Srl

LEEDuser Basic Member

26 thumbs up

Fri, 07/01/2011 - 13:38

Thank you for your answer. But if the software models DCV directly, it means that it use different schedules (if not, there will not be any energy saving on primary airflow). But if I have to use the same schedules (per ASHRAE) theoretically I'm not allowed to modulate fresh rate immission. Really, I don't understand what I have to do. Thank you again. Regards

Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Fri, 07/01/2011 - 14:56

Which modeling software are you using? Does it allow you to directly model DCV? If so just model it. Typically the software bases the OA rate on the occupancy schedule so just make sure your occupancy scheule is identical in both models. SInce this is automatic and well understood no exceptional calculation is required. If your software does not model DCV directly then you would have to make the schedule changes yourself. Since this is a violation of the modeling protocol requiring that schedules be identical, LEED will require you to follow the exceptional calcualtion method. Basically you will need to do separate calculations and write a detailed narrative explaining how you have simulated DCV.