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Zero "Zone Air Terminal Outdoor Air Volume Flow Rate" on design days

asked 2018-09-13 17:20:12 -0500

S gravatar image

updated 2018-09-13 18:47:00 -0500

Hello All, Although I've set outdoor air method in DesignSpecification:OutdoorAir and I used it in Controller:MechanicalVentilation, Sizing:Zone, and AIRTERMINAL:SINGLEDUCT:VAV:REHEAT, the Zone Air Terminal Outdoor Air Volume Flow Rate on my design days are zero. I am using autosized hvac calculation. Any insight would be appreciated.

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Verify that occ schedules are not 0 for the hours for the design runs.

Redux gravatar imageRedux ( 2018-09-14 06:08:11 -0500 )edit

Actually there are internal heat gains from people, lights and so on. And indoor temperature is much higher than the cooling setpoint on summer design day.

S gravatar imageS ( 2018-09-14 06:17:44 -0500 )edit

Do you have any airflow at all from the system?

MJWitte gravatar imageMJWitte ( 2018-09-14 15:12:07 -0500 )edit

How can I check it? Actually on the same day (i.e. summer design day) in the annual simulation run, the "Zone Air Terminal Outdoor Air Volume Flow Rate" is not zero.

S gravatar imageS ( 2018-09-14 15:14:57 -0500 )edit

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answered 2018-09-14 15:43:33 -0500

(idf file was sent to the helpdesk, Ticket 13055).

If you report Fan Electric Power, or System Node Mass Flow Rate, you'll see that the air handler is not operating on the design days. That leads to the airloop AvailabilityManager or the schedule in the supply fan object. The schedule referenced by the fan object is

Always On Discrete,      !- Name
OnOff,                   !- Schedule Type Limits Name
1;                       !- Hourly Value

No problem there. The schedule reference by the AvailabilityManager:Scheduled is

On24/7/Weekdays,         !- Name
OnOff,                   !- Schedule Type Limits Name
Through: 12/31,          !- Field 1
For: Weekdays,           !- Field 2
Until: 24:00,            !- Field 3
1,                       !- Field 4
For: AllOtherDays,       !- Field 5
Until: 24:00,            !- Field 6
0;                       !- Field 7

The day types in the design days are WinterDesignDay and SummerDesignDay, so the above schedule is off on those days. Change "For: Weekdays" to "For: Weekdays WinterDesignDay SummerDesignDay," and the system will run.

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Asked: 2018-09-13 17:20:12 -0500

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Last updated: Sep 14