Outdoor Air Schedule Name in DesignSpecification:OutdoorAir does not work

asked 2023-06-07 02:22:59 -0600

Keigo
4111 ●1 ●48 ●21 https://www.linkedin.c...

I would like to know if there is any use for Outdoor Air Schedule Name in DesignSpecification:OutdoorAir.

I tested how it works with some ExampleFiles:

5ZoneWarmest.idf (Typical VAV with Reheat)
5ZoneFanCoilDOASCool.idf (Typical DOAS + FCU)
VariableRefrigerantFlow_5Zone.idf (Typical VRF)

Each ExampleFile has 5 conditioned Zones. The following input has been unified to all the revised ExampleFiles here (V23-1-0).

Schedule:Compact,
    FanAvailSched,           !- Name
    Fraction,                !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: AllDays,            !- Field 2
    Until: 7:00,             !- Field 3
     0,                      !- Field 4
    Until: 17:00,            !- Field 5
     1,                      !- Field 6
    Until: 24:00,            !- Field 7
     0;                      !- Field 8

Schedule:Compact,
    OutdoorAirAvailSched,    !- Name
    Fraction,                !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: AllDays,            !- Field 2
    Until: 9:00,             !- Field 3
    0.0,                     !- Field 4
    Until: 17:00,            !- Field 5
    1.0,                     !- Field 6
    Until: 24:00,            !- Field 7
    0.0;                     !- Field 8

DesignSpecification:OutdoorAir,
    SZ DSOA SPACE1-1,        !- Name
    flow/person,             !- Outdoor Air Method
    0.00944,                 !- Outdoor Air Flow per Person {m3/s-person}
    0.0,                     !- Outdoor Air Flow per Zone Floor Area {m3/s-m2}
    0.0,                     !- Outdoor Air Flow per Zone {m3/s}
    ,                        !- Outdoor Air Flow Air Changes per Hour {1/hr}
    OutdoorAirAvailSched;    !- Outdoor Air Schedule Name

DesignSpecification:OutdoorAir,
    SZ DSOA SPACE2-1,        !- Name
    flow/person,             !- Outdoor Air Method
    0.00944,                 !- Outdoor Air Flow per Person {m3/s-person}
    0.0,                     !- Outdoor Air Flow per Zone Floor Area {m3/s-m2}
    0.0,                     !- Outdoor Air Flow per Zone {m3/s}
    ,                        !- Outdoor Air Flow Air Changes per Hour {1/hr}
    OutdoorAirAvailSched;    !- Outdoor Air Schedule Name

DesignSpecification:OutdoorAir,
    SZ DSOA SPACE3-1,        !- Name
    flow/person,             !- Outdoor Air Method
    0.00944,                 !- Outdoor Air Flow per Person {m3/s-person}
    0.0,                     !- Outdoor Air Flow per Zone Floor Area {m3/s-m2}
    0.0,                     !- Outdoor Air Flow per Zone {m3/s}
    ,                        !- Outdoor Air Flow Air Changes per Hour {1/hr}
    OutdoorAirAvailSched;    !- Outdoor Air Schedule Name

DesignSpecification:OutdoorAir,
    SZ DSOA SPACE4-1,        !- Name
    flow/person,             !- Outdoor Air Method
    0.00944,                 !- Outdoor Air Flow per Person {m3/s-person}
    0.0,                     !- Outdoor Air Flow per Zone Floor Area {m3/s-m2}
    0.0,                     !- Outdoor Air Flow per Zone {m3/s}
    ,                        !- Outdoor Air Flow Air Changes per Hour {1/hr}
    OutdoorAirAvailSched;    !- Outdoor Air Schedule Name

DesignSpecification:OutdoorAir,
    SZ DSOA SPACE5-1,        !- Name
    flow/person,             !- Outdoor Air Method
    0.00944,                 !- Outdoor Air Flow per Person {m3/s-person}
    0.0,                     !- Outdoor Air Flow per Zone Floor Area {m3/s-m2}
    0.0,                     !- Outdoor Air Flow per Zone {m3/s}
    ,                        !- Outdoor Air Flow Air Changes per Hour {1/hr}
    OutdoorAirAvailSched;    !- Outdoor Air Schedule Name

If Outdoor Air Schedule Name in DesignSpecification:OutdoorAir works, the outdoor air should be supplied to each zone 2 hours after the air supply fan becomes available.

image description

However, the simulation results below show that Outdoor Air Schedule Name has no effect on OA flow rate of each zone during both sizing period and wethrer file run period. image description

Is this a bug?

I know how to control OA flow rate with Schedule. At the system level (AirLoop level), Minimum Outdoor Air Schedule Name in ... (more)

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Comments

Posted issue as https://github.com/NREL/EnergyPlus/issues/10101

Keigo ( 2023-07-08 22:14:21 -0600 )edit

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answered 2023-07-10 09:13:34 -0600

MJWitte

9760 ●6 ●10 http://www.gard.com/

DesignSpecification:OutdoorAir (DSOA) is primarily used for sizing (which ignores the schedule), but it can also be used for control in certain situations:

Controller:MechanicalVentilation references a DSOA for each zone on the system. This is the only way to control the central OA amount based on the schedule in DSOA.
Several air terminal units (`AirTerminal:SingleDuct:VAV:NoReheat, AirTerminal:SingleDuct:VAV:Reheat, AirTerminal:DualDuct:VAV may reference a DSOA object. For VAV terminals, this control will first set the airflow rate based on the thermostat requirement (and the specified minimum flow rate). Then the supply air OA fraction is applied to the supply flow rate to determine the amount of OA the zone will received. If the current DSOA request (including the DSOA schedule) is greater, then the VAV terminal unit will increase the supply airflow in an attempt to meet the OA requirement. Other than changing supply flow rates, there is no feedback to the central system OA controller.
ZoneHVAC:IdealLoadsAirSystem and ZoneHVAC:HybridUnitaryHVAC use a DSOA reference to control OA flow for these single-zone systems.
AirTerminal:SingleDuct:ConstantVolume:NoReheat, AirTerminal:SingleDuct:Mixer, AirTerminal:DualDuct:VAV:OutdoorAir use a DSOA reference to set a flow request from the central air system.

For the example files 5ZoneFanCoilDOASCool_rev and 5ZoneWarmest_Rev, add a Controller:MechanicalVentilation object to control the central OA based on the schedule in the DSOA object.

For the example file VariableRefrigerantFlow_5Zone_rev, the OA flow rate for ZoneHVAC:TerminalUnit:VariableRefrigerantFlow cannot be scheduled. It will be one of three fixed amounts as specified in the "Cooling/Heating/No Load Outdoor Air Flow Rate" fields.

So, this is working as designed, even if it is a bit confusing. As general rule, DesignSpecification:OutdoorAir is only used by the objects which reference it directly.

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Thank you for your answer. I added Controller:MechanicalVentilation to 5ZoneWarmest_rev.idf, but unfortunately, it does not work and I still have outdoor air supply at 8 and 9am. Could you please take a look at my idf file 5ZoneWarmest_rev_MV.idf?

Keigo ( 2023-07-13 03:47:37 -0600 )edit

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