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VAV doesn't introduce any OA once DCV is implemented

asked 2017-10-19 02:24:56 -0600

katsuya.obara's avatar

updated 2017-10-30 01:52:39 -0600

I am modelling VAV with chilled water mainly using HVACTemplate.
After confirming model is working as I expected, tried to implement Demand Control Ventilation referring to this page.
However, it is found that model with DCV doesn't introduce any OA.
Can anyone tell me what may be causing this problem?
Following are the components I have added to the idf file to implement DCV.

    Yes,                     !- Carbon Dioxide Concentration
    Outdoor CO2 Level,       !- Outdoor Carbon Dioxide Schedule Name
    No;                      !- Generic Contaminant Concentration

    A_LZ_OfficeN,            !- Name
    A_LZ_OfficeN,            !- Zone Name
    All On,                  !- Carbon Dioxide Control Availability Schedule Name
    CO2 Sensor On;           !- Carbon Dioxide Setpoint Schedule Name

    Office_DCV,              !- Name
    CO2 Sensor On,           !- Availability Schedule Name
    Yes,                     !- Demand Controlled Ventilation
    IndoorAirQualityProcedure,  !- System Outdoor Air Method
    1,                       !- Zone Maximum Outdoor Air Fraction {dimensionless}
    Office_list,             !- Zone 1 Name
    Office_OA,               !- Design Specification Outdoor Air Object Name 1
    DSZAD;                   !- Design Specification Zone Air Distribution Object Name 1

    A_LZ_Sys OA Controller,  !- Name
    A_LZ_Sys Relief Air Outlet,  !- Relief Air Outlet Node Name
    A_LZ_Sys Air Loop Inlet, !- Return Air Node Name
    A_LZ_Sys Mixed Air Outlet,  !- Mixed Air Node Name
    A_LZ_Sys Outside Air Inlet,  !- Actuator Node Name
    autosize,                !- Minimum Outdoor Air Flow Rate {m3/s}
    autosize,                !- Maximum Outdoor Air Flow Rate {m3/s}
    NoEconomizer,            !- Economizer Control Type
    ModulateFlow,            !- Economizer Control Action Type
    ,                        !- Economizer Maximum Limit Dry-Bulb Temperature {C}
    ,                        !- Economizer Maximum Limit Enthalpy {J/kg}
    ,                        !- Economizer Maximum Limit Dewpoint Temperature {C}
    ,                        !- Electronic Enthalpy Limit Curve Name
    ,                        !- Economizer Minimum Limit Dry-Bulb Temperature {C}
    NoLockout,               !- Lockout Type
    FixedMinimum,            !- Minimum Limit Type
    ,                        !- Minimum Outdoor Air Schedule Name
    ,                        !- Minimum Fraction of Outdoor Air Schedule Name
    On,                      !- Maximum Fraction of Outdoor Air Schedule Name
    Office_DCV;              !- Mechanical Ventilation Controller Name

    CO2 Sensor On,           !- Name
    Any Number,              !- Schedule Type Limits Name
    Through: 31 Dec,         !- Field 1
    For: Weekdays,           !- Field 2
    Until: 5:00,             !- Field 3
    0,                       !- Field 4
    Until: 22:00,            !- Field 5
    1000,                    !- Field 6
    Until: 24:00,            !- Field 7
    0,                       !- Field 8
    For: Saturday,           !- Field 9
    Until: 5:00,             !- Field 10
    0,                       !- Field 11
    Until: 15:00,            !- Field 12
    1000,                    !- Field 13
    Until: 24:00,            !- Field 14
    0,                       !- Field 15
    For: SummerDesignDay,    !- Field 16
    Until: 5:00,             !- Field 17
    0,                       !- Field 18
    Until: 22:00,            !- Field 19
    1000,                    !- Field 20
    Until: 24:00,            !- Field 21
    0,                       !- Field 22
    For: WinterDesignDay,    !- Field 23
    Until: 5:00,             !- Field 24
    0,                       !- Field 25
    Until: 22:00,            !- Field 26
    1000,                    !- Field 27
    Until: 24:00,            !- Field 28
    0,                       !- Field 29
    For: AllOtherDays,       !- Field 30
    Until: 24:00,            !- Field 31
    0;                       !- Field 32

    Outdoor CO2 Level,       !- Name
    Any Number,              !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: AllDays,            !- Field 2
    Until: 24:00,            !- Field 3
    400;                     !- Field 4

    All on,                  !- Name
    On/Off,                  !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: AllDays,            !- Field 2
    Until: 24:00,            !- Field 3
    1;                       !- Field 4

    On,                      !- Name
    Any Number,              !- Schedule Type Limits Name
    1;                       !- Hourly Value

    Office_ppl,              !- Name
    Office_list,             !- Zone or ZoneList Name
    Office ppl (BEAM),       !- Number of ...
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Please also post these relevant objects: "Office_OA", "CO2 Sensor On", "Outdoor CO2 Level", "All On", "On" and also the relevant People object which specifies a CO2 generation rate for the "Office_list" zones and the Activity Level Schedule referenced by that People object.

Molly Curtz's avatar Molly Curtz  ( 2017-10-19 17:24:01 -0600 )edit

I have added the objects to the post. However, I cannot find objects in DesignSpecification:OutdoorAir as shown the image added to the above post though I can find them in idf editor.

katsuya.obara's avatar katsuya.obara  ( 2017-10-19 19:35:26 -0600 )edit

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answered 2017-10-20 12:34:02 -0600

Molly Curtz's avatar

The input in Controller:OutdoorAir object field "Minimum Outdoor Airflow Rate" and "Maximum Outdoor Airflow Rate" are both set to "Autosize".

The Autosizing for "Minimum Outdoor Airflow Rate" is based on your inputs in the DesignSpecification:OutdoorAir object referenced by the Sizing:Zone object, and is also influenced by your input in the "System Outdoor Air Method" field of the Sizing:System object. Given that you have selected "NoEconomizer" for the input to "Economizer Control Type" it may be reasonable the "Maximum Outdoor Airflow Rate" when Autosized could be identical to the "Minimum Outdoor Airflow Rate" but I have not confirmed this. You might want to try including an economizer to see if that impacts the Autosizing of "Maximum Outdoor Airflow Rate"? Once there is an Economizer I'd expect that would Autosize to the system design flow rate.

Change the input the in Controller:OutdoorAir object field "Minimum Outdoor Airflow Rate" from "Autosize" to zero ("0") to allow modulation of outdoor airflow based on the IndoorAirQualityProcedure input in the Controller:MechanicalVentilation object.

You can also assess the CO2 setpoint you have used relative to the design sizing of OSA per person that you are delivering ( specified in the DesignSpecification:OutdoorAir object) by looking at the steady state CO2 concentration maintained by the OSA/person delivered. image description

And look at the output:variable for Zone Air CO2 Concentration to see if your setpoint is maintained.

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Thanks for your input. I have tried to change the in Controller:OutdoorAir object field "Minimum Outdoor Airflow Rate" from "Autosize" to zero ("0") and checked Zone Air CO2 Concentration and Zone Air CO2 Setpoint Concentration. But result seems they still don't introduce OA as shown added image to my question (since I didn't know how to attach image file to this comment)

katsuya.obara's avatar katsuya.obara  ( 2017-10-30 01:49:11 -0600 )edit

Zone Air CO2 is climbing at a constant rate in the graph you posted, indicating zero introduction of OA to the zone. First zoom into a single day to see if there is any variation in the rate of change in the concentration (any drop in the concentration would indicate OA is introduced to the zone). IF that still shows a steady climb (or zero change, when system OFF) in CO2 concentration, then, Next I would check: Do you have system flow? Do you have any OA at the system? Do you have airflow entering the zone? And, verify the zone you are looking at is connected to a system with DCV

Molly Curtz's avatar Molly Curtz  ( 2017-10-31 11:01:47 -0600 )edit

Also, Graph the system total flow and system OA flow. Is it operating at 100% OSA at the system? If not what is the maximum OSA percentage?

Molly Curtz's avatar Molly Curtz  ( 2017-10-31 11:03:35 -0600 )edit

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Asked: 2017-10-19 02:24:56 -0600

Seen: 384 times

Last updated: Oct 30 '17