Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.Economizers.Subsequences
Subsequences for economizer control
Information
This package contains subsequences for single zone VAV AHU economizer control.
Package Content
| Name | Description |
|---|---|
 Enable
|
Single zone VAV AHU economizer enable/disable switch |
 Limits
|
Single zone VAV AHU minimum outdoor air control - damper position limits |
 Modulation
|
Outdoor and return air damper position modulation sequence for single zone VAV AHU |
 Validation
|
Collection of validation models |
Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.Economizers.Subsequences.Enable
Single zone VAV AHU economizer enable/disable switch
Information
This is a single zone VAV AHU economizer enable/disable sequence based on Section 5.18.7 and Section 5.1.17 of ASHRAE Guideline 36, May 2020. Additional conditions included in the sequence are:
- Buildings.Controls.OBC.ASHRAE.G36.Types.FreezeProtectionStages,
-
Supply fan status
u1SupFan, - Buildings.Controls.OBC.ASHRAE.G36.Types.ZoneStates.
The economizer is disabled whenever the outdoor air conditions
exceed the economizer high limit cutoff setpoint plus the hysteresis low limit parameter
(TOutHigLimCutLow or hOutHigLimCutLow) as shown in the figure.
And the economizer is enabled whenever the outdoor air conditions are below the economizer
high limit cutoff setpoint plus the hysteresis high limit parameter (TOutHigLimCutHig or
hOutHigLimCutHig). This sequence allows for all device types listed in
ASHRAE 90.1-2013 and Title 24-2013.
In addition, the economizer is disabled without a delay whenever any of the
following is true:
- supply fan is off,
-
zone state is
heating, -
freeze protection stage is not
0.
The following state machine chart illustrates the transitions between enabling and disabling:
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Conditional | |||
| Boolean | use_enthalpy | true | Set to true to evaluate outdoor air (OA) enthalpy in addition to temperature |
| Advanced | |||
| Hysteresis | |||
| Real | delTOutHys | 1 | Delta between the temperature hysteresis high and low limit [K] |
| Real | delEntHys | 1000 | Delta between the enthalpy hysteresis high and low limits [J/kg] |
| Commissioning | |||
| Physical damper position limits | |||
| Real | retDamPhy_max | 1 | Physically fixed maximum position of the return air damper [1] |
| Real | retDamPhy_min | 0 | Physically fixed minimum position of the return air damper [1] |
Connectors
| Type | Name | Description |
|---|---|---|
| input RealInput | TOut | Outdoor air temperature [K] |
| input RealInput | TCut | OA temperature high limit cutoff. For differential dry bulb temperature condition use return air temperature measurement [K] |
| input RealInput | hOut | Outdoor air enthalpy [J/kg] |
| input RealInput | hCut | OA enthalpy high limit cutoff. For differential enthalpy use return air enthalpy measurement [J/kg] |
| input BooleanInput | u1SupFan | Supply fan on/off status signal |
| input IntegerInput | uFreProSta | Freeze protection stage status signal |
| input IntegerInput | uZonSta | Zone state status signal |
| input RealInput | uOutDam_max | Maximum outdoor air damper position, get from damper position limits sequence [1] |
| input RealInput | uOutDam_min | Minimum outdoor air damper position, get from damper position limits sequence [1] |
| output RealOutput | yOutDam_max | Maximum outdoor air damper position [1] |
| output RealOutput | yRetDam_max | Maximum return air damper position [1] |
| output RealOutput | yRetDam_min | Minimum return air damper position [1] |
Modelica definition
block Enable
"Single zone VAV AHU economizer enable/disable switch"
parameter Boolean use_enthalpy = true
"Set to true to evaluate outdoor air (OA) enthalpy in addition to temperature";
parameter Real delTOutHys(
final unit="K",
final displayUnit="K",
final quantity="TemperatureDifference")=1
"Delta between the temperature hysteresis high and low limit";
parameter Real delEntHys(
final unit="J/kg",
final quantity="SpecificEnergy")=1000
"Delta between the enthalpy hysteresis high and low limits";
parameter Real retDamPhy_max(
final min=0,
final max=1,
final unit="1") = 1
"Physically fixed maximum position of the return air damper";
parameter Real retDamPhy_min(
final min=0,
final max=1,
final unit="1") = 0
"Physically fixed minimum position of the return air damper";
Buildings.Controls.OBC.CDL.Interfaces.RealInput TOut(
final unit="K",
final displayUnit="degC",
final quantity = "ThermodynamicTemperature")
"Outdoor air temperature";
Buildings.Controls.OBC.CDL.Interfaces.RealInput TCut(
final unit="K",
final displayUnit="degC",
final quantity="ThermodynamicTemperature")
"OA temperature high limit cutoff. For differential dry bulb temperature condition use return air temperature measurement";
Buildings.Controls.OBC.CDL.Interfaces.RealInput hOut(
final unit="J/kg",
final quantity="SpecificEnergy") if use_enthalpy
"Outdoor air enthalpy";
Buildings.Controls.OBC.CDL.Interfaces.RealInput hCut(
final unit="J/kg",
final quantity="SpecificEnergy") if use_enthalpy
"OA enthalpy high limit cutoff. For differential enthalpy use return air enthalpy measurement";
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput u1SupFan
"Supply fan on/off status signal";
Buildings.Controls.OBC.CDL.Interfaces.IntegerInput uFreProSta
"Freeze protection stage status signal";
Buildings.Controls.OBC.CDL.Interfaces.IntegerInput uZonSta
"Zone state status signal";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uOutDam_max(
final unit="1",
final min=0,
final max=1)
"Maximum outdoor air damper position, get from damper position limits sequence";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uOutDam_min(
final unit="1",
final min=0,
final max=1)
"Minimum outdoor air damper position, get from damper position limits sequence";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yOutDam_max(
final min=0,
final max=1,
final unit="1")
"Maximum outdoor air damper position";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yRetDam_max(
final min=retDamPhy_min,
final max=retDamPhy_max,
final unit="1")
"Maximum return air damper position";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yRetDam_min(
final min=retDamPhy_min,
final max=retDamPhy_max,
final unit="1")
"Minimum return air damper position";
Buildings.Controls.OBC.CDL.Logical.And3 andEnaDis
"Logical and that checks freeze protection stage and zone state";
Buildings.Controls.OBC.CDL.Logical.TrueFalseHold truFalHol(
trueHoldDuration=600) "10 min on/off delay";
protected
final parameter Real TOutHigLimCutHig(
final unit="K",
final displayUnit="K",
final quantity="TemperatureDifference") = 0
"Hysteresis high limit cutoff";
final parameter Real TOutHigLimCutLow = TOutHigLimCutHig - delTOutHys
"Hysteresis low limit cutoff";
final parameter Real hOutHigLimCutHig(
final unit="J/kg",
final quantity="SpecificEnergy") = 0
"Hysteresis block high limit cutoff";
final parameter Real hOutHigLimCutLow = hOutHigLimCutHig - delEntHys
"Hysteresis block low limit cutoff";
Buildings.Controls.OBC.CDL.Logical.Sources.Constant entSubst(
final k=false) if not use_enthalpy
"Deactivates outdoor air enthalpy condition if there is no enthalpy sensor";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant retDamPhyMin(
final k=retDamPhy_min)
"Physically fixed minimum position of the return air damper";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant retDamPhyMax(
final k=retDamPhy_max)
"Physically fixed maximum position of the return air damper. This is the initial condition of the return air damper";
Buildings.Controls.OBC.CDL.Continuous.Hysteresis hysOutTem(
final uHigh=TOutHigLimCutHig,
final uLow=TOutHigLimCutLow)
"Outdoor air temperature hysteresis for fixed or differential dry bulb temperature cutoff conditions";
Buildings.Controls.OBC.CDL.Continuous.Hysteresis hysOutEnt(
final uLow=hOutHigLimCutLow,
final uHigh=hOutHigLimCutHig) if use_enthalpy
"Outdoor air enthalpy hysteresis for fixed or differential enthalpy cutoff conditions";
Buildings.Controls.OBC.CDL.Continuous.Subtract sub2 if use_enthalpy
"Add block that determines the difference between hOut and hOutCut";
Buildings.Controls.OBC.CDL.Continuous.Subtract sub1
"Add block that determines difference the between TOut and TOutCut";
Buildings.Controls.OBC.CDL.Continuous.Switch maxOutDam
"Set maximum OA damper position to minimum at disable (after time delay)";
Buildings.Controls.OBC.CDL.Continuous.Switch minRetDam
"Keep minimum RA damper position at physical maximum for a short time period after disable";
Buildings.Controls.OBC.CDL.Logical.Not not2
"Logical not that starts the timer at disable signal ";
Buildings.Controls.OBC.CDL.Logical.And and1 "Logical and checks supply fan status";
Buildings.Controls.OBC.CDL.Integers.Sources.Constant conInt(
final k=Buildings.Controls.OBC.ASHRAE.G36.Types.FreezeProtectionStages.stage0)
"Freeze protection stage 0";
Buildings.Controls.OBC.CDL.Integers.Equal intEqu
"Logical block to check if the freeze protection is deactivated";
Buildings.Controls.OBC.CDL.Integers.Sources.Constant conInt1(
final k=Buildings.Controls.OBC.ASHRAE.G36.Types.ZoneStates.heating)
"Heating zone state";
Buildings.Controls.OBC.CDL.Integers.Equal intEqu1
"Logical block to check if the freeze protection is deactivated";
Buildings.Controls.OBC.CDL.Logical.Not not3
"Negation for check of freeze protection status";
Buildings.Controls.OBC.CDL.Logical.Or or2
"Check if either the temperature or the enthalpy condition is satisfied";
equation
connect(maxOutDam.y, yOutDam_max);
connect(TOut, sub1.u1);
connect(TCut, sub1.u2);
connect(sub1.y, hysOutTem.u);
connect(hOut, sub2.u1);
connect(hCut, sub2.u2);
connect(sub2.y, hysOutEnt.u);
connect(uOutDam_min, maxOutDam.u1);
connect(uOutDam_max, maxOutDam.u3);
connect(andEnaDis.y, not2.u);
connect(minRetDam.y, yRetDam_min);
connect(truFalHol.y, and1.u1);
connect(and1.y, andEnaDis.u1);
connect(u1SupFan, and1.u2);
connect(retDamPhyMax.y, minRetDam.u1);
connect(retDamPhyMin.y, minRetDam.u3);
connect(retDamPhyMax.y, yRetDam_max);
connect(not2.y, minRetDam.u2);
connect(not2.y, maxOutDam.u2);
connect(conInt.y,intEqu. u2);
connect(conInt1.y,intEqu1. u2);
connect(intEqu1.y,not3. u);
connect(uZonSta, intEqu1.u1);
connect(uFreProSta, intEqu.u1);
connect(intEqu.y, andEnaDis.u2);
connect(not3.y, andEnaDis.u3);
connect(hysOutTem.y, or2.u1);
connect(hysOutEnt.y, or2.u2);
connect(entSubst.y, or2.u2);
connect(or2.y, truFalHol.u);
end Enable;
Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.Economizers.Subsequences.Limits
Single zone VAV AHU minimum outdoor air control - damper position limits
Information
This block implements the single zone VAV AHU minimum outdoor air control with a single
common damper for minimum outdoor air and economizer functions based on outdoor airflow
setpoint (VOutMinSet_flow) and supply fan speed (uSupFanSpe_actual),
designed in line with Section 5.18.6 of ASHRAE Guidline 36, May 2020.
The controller is enabled when the supply fan is proven on (u1SupFan=true),
the AHU operation mode uOpeMod is Occupied, and Freeze protection stage
uFreProSta is 1 or smaller. Otherwise the damper position limits are set to
their corresponding maximum and minimum physical or at commissioning fixed limits, as illustrated below:
If limit modulation is enabled, the outdoor air damper position yOutDamPosMin is computed as
follows:
-
Calculate outdoor air damper position
yDam_VOutMin_curSpewhich ensures minimum outdoor airflow rateVOutMin_flowat current supply fan speeduSupFanSpe_actualas a linear interpolation between the following values set at commissioning:
- minimum damper position at minimum fan speed for minimum outdoor airflow
outDamMinFloMinSpeand -
minimum damper position at maximum fan speed for minimum outdoor airflow
outDamMinFloMaxSpe.
- minimum damper position at minimum fan speed for minimum outdoor airflow
-
Calculate outdoor air damper position
yDam_VOutDes_curSpewhich ensures design outdoor airflow rateVOutDes_flowat current supply fan speeduSupFanSpe_actual, as a linear interpolation between the following values set at commissioning:
-
minimum damper position at minimum fan speed for design outdoor airflow
outDamDesFloMinSpeand -
minimum damper position at maximum fan speed for design outdoor airflow
outDamDesFloMaxSpe.
-
minimum damper position at minimum fan speed for design outdoor airflow
-
Calculate outdoor air damper position
yOutDamPosMinwhich ensures outdoor airflow setpointVOutMinSet_flowat current supply fan speeduSupFanSpe_actualas a linear interpolation betweenyDam_VOutMin_curSpeandyDam_VOutDes_curSpe, proportional to ratios ofVOutMinSet_flowtoVOutDes_flowandVOutMin_flow. -
If outdoor airflow setpoint
VOutMinSet_flowis zero,yOutDamPosMinshould be zero.
The chart below illustrates the OA damper position limit calculation:
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Commissioning | |||
| Damper position limits | |||
| Real | supFanSpe_min | 0.1 | Minimum supply fan operation speed [1] |
| Real | supFanSpe_max | 1 | Maximum supply fan operation speed [1] |
| Real | outDamMinFloMinSpe | 0.4 | OA damper position to supply minimum outdoor airflow at minimum fan speed [1] |
| Real | outDamMinFloMaxSpe | 0.3 | OA damper position to supply minimum outdoor airflow at maximum fan speed [1] |
| Real | outDamDesFloMinSpe | 0.9 | OA damper position to supply design outdoor airflow at minimum fan speed [1] |
| Real | outDamDesFloMaxSpe | 0.8 | OA damper position to supply design outdoor airflow at maximum fan speed [1] |
| Real | VOutMin_flow | Calculated minimum outdoor airflow rate [m3/s] | |
| Real | VOutDes_flow | Calculated design outdoor airflow rate [m3/s] | |
| Physical damper position limits | |||
| Real | outDamPhy_max | 1 | Physically fixed maximum position of the outdoor air damper [1] |
| Real | outDamPhy_min | 0 | Physically fixed minimum position of the outdoor air damper [1] |
| Advanced | |||
| Real | floHys | 0.01 | Near zero flow rate, below which the flow rate or difference will be seen as zero [m3/s] |
Connectors
| Type | Name | Description |
|---|---|---|
| input RealInput | uSupFan_actual | Actual supply fan speed [1] |
| input RealInput | VOutMinSet_flow | Minimum outdoor airflow setpoint [m3/s] |
| input IntegerInput | uOpeMod | AHU operation mode status signal |
| input IntegerInput | uFreProSta | Freeze protection status signal |
| input BooleanInput | u1SupFan | Supply fan status signal |
| output RealOutput | yOutDam_min | Minimum outdoor air damper position limit [1] |
| output RealOutput | yOutDam_max | Maximum outdoor air damper position limit [1] |
Modelica definition
block Limits "Single zone VAV AHU minimum outdoor air control - damper position limits"
parameter Real supFanSpe_min(
final min=0,
final max=1,
final unit="1") = 0.1 "Minimum supply fan operation speed";
parameter Real supFanSpe_max(
final min=0,
final max=1,
final unit="1") = 1 "Maximum supply fan operation speed";
parameter Real outDamMinFloMinSpe(
final min=outDamPhy_min,
final max=outDamPhy_max,
final unit="1") = 0.4
"OA damper position to supply minimum outdoor airflow at minimum fan speed";
parameter Real outDamMinFloMaxSpe(
final min=outDamPhy_min,
final max=outDamPhy_max,
final unit="1") = 0.3
"OA damper position to supply minimum outdoor airflow at maximum fan speed";
parameter Real outDamDesFloMinSpe(
final min=outDamMinFloMinSpe,
final max=outDamPhy_max,
final unit="1") = 0.9
"OA damper position to supply design outdoor airflow at minimum fan speed";
parameter Real outDamDesFloMaxSpe(
final min=outDamMinFloMaxSpe,
final max=outDamPhy_max,
final unit="1") = 0.8
"OA damper position to supply design outdoor airflow at maximum fan speed";
parameter Real VOutMin_flow(
final unit="m3/s",
final quantity="VolumeFlowRate") "Calculated minimum outdoor airflow rate";
parameter Real VOutDes_flow(
final unit="m3/s",
final quantity="VolumeFlowRate")
"Calculated design outdoor airflow rate";
parameter Real outDamPhy_max(
final min=0,
final max=1,
final unit="1") = 1
"Physically fixed maximum position of the outdoor air damper";
parameter Real outDamPhy_min(
final min=0,
final max=1,
final unit="1") = 0
"Physically fixed minimum position of the outdoor air damper";
parameter Real floHys(
final unit="m3/s",
final quantity="VolumeFlowRate")=0.01
"Near zero flow rate, below which the flow rate or difference will be seen as zero";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uSupFan_actual(
final min=0,
final max=1,
final unit="1")
"Actual supply fan speed";
Buildings.Controls.OBC.CDL.Interfaces.RealInput VOutMinSet_flow(
final unit="m3/s",
final quantity="VolumeFlowRate",
final min=VOutMin_flow,
final max=VOutDes_flow)
"Minimum outdoor airflow setpoint";
Buildings.Controls.OBC.CDL.Interfaces.IntegerInput uOpeMod
"AHU operation mode status signal";
Buildings.Controls.OBC.CDL.Interfaces.IntegerInput uFreProSta
"Freeze protection status signal";
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput u1SupFan
"Supply fan status signal";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yOutDam_min(
final min=outDamPhy_min,
final max=outDamPhy_max,
final unit="1") "Minimum outdoor air damper position limit";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yOutDam_max(
final min=outDamPhy_min,
final max=outDamPhy_max,
final unit="1") "Maximum outdoor air damper position limit";
protected
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant yFanMinSig(
final k=supFanSpe_min) "Minimum supply fan speed";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant outDamPhyPosMinSig(
final k=outDamPhy_min)
"Physically fixed minimum position of the outdoor air damper";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant outDamPhyPosMaxSig(
final k=outDamPhy_max)
"Physically fixed maximum position of the outdoor air damper";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant yFanMaxSig(
final k=supFanSpe_max) "Maximum supply fan speed";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant yDam_VOutMin_minSpeSig(
final k=outDamMinFloMinSpe)
"OA damper position to supply minimum outdoor airflow at minimum fan speed";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant yDam_VOutDes_minSpeSig(
final k=outDamDesFloMinSpe)
"OA damper position to supply design outdoor airflow at minimum fan speed";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant yDam_VOutMin_maxSpeSig(
final k=outDamMinFloMaxSpe)
"OA damper position to supply minimum outdoor airflow at maximum fan speed";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant yDam_VOutDes_maxSpeSig(
final k=outDamDesFloMaxSpe)
"OA damper position to supply design outdoor airflow at maximum fan speed";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant minVOutSig(
final k=VOutMin_flow) "Minimum outdoor airflow rate";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant desVOutSig(
final k=VOutDes_flow) "Design outdoor airflow rate";
Buildings.Controls.OBC.CDL.Continuous.Line yDam_VOutMin_curSpe(
final limitBelow=true,
final limitAbove=true)
"Calculates OA damper position required to supply minimum outdoor airflow at current fan speed";
Buildings.Controls.OBC.CDL.Continuous.Line yDam_VOutDes_curSpe(
final limitBelow=true,
final limitAbove=true)
"Calculates OA damper position required to supply design outdoor airflow at current fan speed";
Buildings.Controls.OBC.CDL.Continuous.Line minVOutSetCurFanSpePos(
final limitBelow=true,
final limitAbove=true)
"Calculates OA damper position required to supply minimum outdoor airflow setpoint at current fan speed";
Buildings.Controls.OBC.CDL.Continuous.Switch enaDis
"Logical switch to enable damper position limit calculation or disable it (set min limit to physical minimum)";
Buildings.Controls.OBC.CDL.Logical.Not not1 "Logical not block";
Buildings.Controls.OBC.CDL.Continuous.Switch enaDis1
"Logical switch to enable damper position limit calculation or disable it (set max limit to physical minimum)";
Buildings.Controls.OBC.CDL.Integers.Sources.Constant conInt(
final k=Buildings.Controls.OBC.ASHRAE.G36.Types.FreezeProtectionStages.stage1)
"Freeze protection stage 1";
Buildings.Controls.OBC.CDL.Integers.LessEqual intLesEqu
"Check if freeze protection stage is stage 0";
Buildings.Controls.OBC.CDL.Integers.Sources.Constant conInt1(
final k=Buildings.Controls.OBC.ASHRAE.G36.Types.OperationModes.occupied)
"Occupied mode index";
Buildings.Controls.OBC.CDL.Integers.Equal intEqu1 "Check if operation mode is occupied";
Buildings.Controls.OBC.CDL.Logical.And3 and3 "Logical and";
Buildings.Controls.OBC.CDL.Continuous.Switch enaDis2
"Zero minimum damper position when the min OA is near zero";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant zer(
final k=0)
"Zero minimum damper position";
Buildings.Controls.OBC.CDL.Continuous.GreaterThreshold noZerMin(
final t=floHys,
final h=0.5*floHys) "Check if the min OA is greater than zero";
equation
connect(minVOutSig.y, minVOutSetCurFanSpePos.x1);
connect(desVOutSig.y, minVOutSetCurFanSpePos.x2);
connect(yDam_VOutMin_curSpe.y, minVOutSetCurFanSpePos.f1);
connect(yDam_VOutDes_curSpe.y, minVOutSetCurFanSpePos.f2);
connect(yDam_VOutDes_minSpeSig.y, yDam_VOutDes_curSpe.f1);
connect(yDam_VOutDes_maxSpeSig.y, yDam_VOutDes_curSpe.f2);
connect(yDam_VOutMin_minSpeSig.y, yDam_VOutMin_curSpe.f1);
connect(yDam_VOutMin_maxSpeSig.y, yDam_VOutMin_curSpe.f2);
connect(uSupFan_actual, yDam_VOutMin_curSpe.u);
connect(yFanMaxSig.y, yDam_VOutMin_curSpe.x2);
connect(yFanMinSig.y, yDam_VOutMin_curSpe.x1);
connect(yFanMinSig.y, yDam_VOutDes_curSpe.x1);
connect(yFanMaxSig.y, yDam_VOutDes_curSpe.x2);
connect(VOutMinSet_flow, minVOutSetCurFanSpePos.u);
connect(uSupFan_actual, yDam_VOutDes_curSpe.u);
connect(not1.y, enaDis.u2);
connect(outDamPhyPosMinSig.y, enaDis.u1);
connect(minVOutSetCurFanSpePos.y, enaDis.u3);
connect(outDamPhyPosMinSig.y, enaDis1.u1);
connect(outDamPhyPosMaxSig.y, enaDis1.u3);
connect(enaDis1.y, yOutDam_max);
connect(not1.y, enaDis1.u2);
connect(uOpeMod, intEqu1.u1);
connect(conInt1.y, intEqu1.u2);
connect(intLesEqu.u2, conInt.y);
connect(uFreProSta, intLesEqu.u1);
connect(u1SupFan, and3.u1);
connect(intLesEqu.y, and3.u2);
connect(intEqu1.y, and3.u3);
connect(and3.y, not1.u);
connect(VOutMinSet_flow, noZerMin.u);
connect(noZerMin.y, enaDis2.u2);
connect(enaDis.y, enaDis2.u1);
connect(enaDis2.y, yOutDam_min);
connect(zer.y, enaDis2.u3);
end Limits;
Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.Economizers.Subsequences.Modulation
Outdoor and return air damper position modulation sequence for single zone VAV AHU
Information
This is a single zone VAV AHU economizer modulation block. It calculates the outdoor and return air damper positions based on the single zone VAV AHU supply air temperature control loop signal. Economizer dampers are modulated based on the calculated heating supply air temperature setpoint. The implementation is in line with Section 5.18.5.1 and 5.18.5.2 of ASHRAE Guidline 36, May 2020. Damper positions are linearly mapped to the supply air control loop signal. This is a final sequence in the composite single zone VAV AHU economizer control sequence. Damper position limits, which are the inputs to the sequence, are the outputs of Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.Economizers.Subsequences.Limits and Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.Economizers.Subsequences.Enable sequences.
When the economizer is enabled, the PI controller modulates the damper positions. Return and outdoor damper are not interlocked. When the economizer is disabled, the damper positions are set to the minimum outdoor air damper position limits.
The figures below show the input-output structure and an economizer damper modulation sequence assuming a well configured controller.
Control diagram:
Single zone AHU economizer modulation control chart:
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Boolean | have_heaCoi | true | True if the air handling unit has heating coil |
| SimpleController | controllerType | Buildings.Controls.OBC.CDL.T... | Type of controller |
| Real | k | 1 | Gain of controller [1/K] |
| Real | Ti | 300 | Time constant of modulation controller integrator block [s] |
| Real | Td | 0.1 | Time constant of derivative block for cooling control loop signal [s] |
| Real | uMin | 0.1 | Lower limit of controller output uTSup at which the dampers are at their limits [1] |
| Real | uMax | 0.9 | Upper limit of controller output uTSup at which the dampers are at their limits [1] |
Connectors
| Type | Name | Description |
|---|---|---|
| input RealInput | TSup | Measured supply air temperature [K] |
| input RealInput | TSupHeaEcoSet | Supply air temperature heating setpoint [K] |
| input BooleanInput | u1SupFan | Supply fan status |
| input RealInput | uOutDam_min | Minimum economizer damper position limit as returned by the damper position limits sequence [1] |
| input RealInput | uOutDam_max | Maximum economizer damper position limit as returned by the economizer enable-disable sequence. If the economizer is disabled, this value equals uOutDamPosMin [1] |
| input RealInput | uRetDam_min | Minimum return air damper position limit as returned by the economizer enable-disable sequence [1] |
| input RealInput | uRetDam_max | Maximum return air damper position limit as returned by the economizer enable-disable sequence [1] |
| output RealOutput | yHeaCoi | Heating coil commanded valve position [1] |
| output RealOutput | yOutDam | Economizer damper commanded position [1] |
| output RealOutput | yRetDam | Return air damper commanded position [1] |
Modelica definition
block Modulation "Outdoor and return air damper position modulation sequence for single zone VAV AHU"
parameter Boolean have_heaCoi = true
"True if the air handling unit has heating coil";
parameter Buildings.Controls.OBC.CDL.Types.SimpleController controllerType=
Buildings.Controls.OBC.CDL.Types.SimpleController.PI
"Type of controller";
parameter Real k(
final unit="1/K") = 1 "Gain of controller";
parameter Real Ti(
final unit="s",
final quantity="Time")=300
"Time constant of modulation controller integrator block";
parameter Real Td(
final unit="s",
final quantity="Time")=0.1
"Time constant of derivative block for cooling control loop signal";
parameter Real uMin(
final min=0.1,
final max=0.9,
final unit="1") = 0.1
"Lower limit of controller output uTSup at which the dampers are at their limits";
parameter Real uMax(
final min=0.1,
final max=1,
final unit="1") = 0.9
"Upper limit of controller output uTSup at which the dampers are at their limits";
Buildings.Controls.OBC.CDL.Interfaces.RealInput TSup(
final unit="K",
final displayUnit="degC",
final quantity = "ThermodynamicTemperature")
"Measured supply air temperature";
Buildings.Controls.OBC.CDL.Interfaces.RealInput TSupHeaEcoSet(
final unit="K",
final displayUnit="degC",
final quantity="ThermodynamicTemperature")
"Supply air temperature heating setpoint";
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput u1SupFan
"Supply fan status";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uOutDam_min(
final min=0,
final max=1,
final unit="1")
"Minimum economizer damper position limit as returned by the damper position limits sequence";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uOutDam_max(
final min=0,
final max=1,
final unit="1") "Maximum economizer damper position limit as returned by the economizer enable-disable sequence.
If the economizer is disabled, this value equals uOutDamPosMin";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uRetDam_min(
final min=0,
final max=1,
final unit="1")
"Minimum return air damper position limit as returned by the economizer enable-disable sequence";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uRetDam_max(
final min=0,
final max=1,
final unit="1")
"Maximum return air damper position limit as returned by the economizer enable-disable sequence";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yHeaCoi(
final min=0,
final max=1,
final unit="1") if have_heaCoi "Heating coil commanded valve position";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yOutDam(
final min=0,
final max=1,
final unit="1") "Economizer damper commanded position";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yRetDam(
final min=0,
final max=1,
final unit="1") "Return air damper commanded position";
Buildings.Controls.OBC.CDL.Continuous.PIDWithReset uTSup(
final controllerType=controllerType,
final k=k,
final Ti=Ti,
final Td=Td,
final yMax=1,
final yMin=0)
"Contoller that outputs a signal based on the error between the measured SAT and SAT heating setpoint";
protected
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant outDamMinLimSig(
final k=uMin) "Minimal control loop signal for the outdoor air damper";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant retDamMaxLimSig(
final k=uMax) "Maximal control loop signal for the return air damper";
Buildings.Controls.OBC.CDL.Continuous.Line outDamPos(
final limitBelow=true,
final limitAbove=true)
"Damper position is linearly proportional to the control signal between signal limits";
Buildings.Controls.OBC.CDL.Continuous.Line retDamPos(
final limitBelow=true,
final limitAbove=true)
"Damper position is linearly proportional to the control signal between signal limits";
Buildings.Controls.OBC.CDL.Continuous.Line HeaCoi(
final limitBelow=true,
final limitAbove=true) if have_heaCoi
"Heating coil signal is linearly proportional to the control signal between signal limits";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant heaCoiMaxLimSig(
final k=1) if have_heaCoi
"Maximal control loop signal for the heating coil";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant heaCoiMinLimSig(
final k=0) if have_heaCoi
"Minimum control loop signal for the heating coil";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant uMaxHeaCoi(
final k=1)
"Maximal control loop signal for the heating coil";
Buildings.Controls.OBC.CDL.Continuous.Switch enaDis if have_heaCoi
"Enable or disable the heating coil";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant Off(
final k=0) if have_heaCoi
"Off signal for heating coil";
equation
connect(retDamMaxLimSig.y,retDamPos. x2);
connect(uTSup.y, retDamPos.u);
connect(uTSup.y, outDamPos.u);
connect(outDamMinLimSig.y, outDamPos.x1);
connect(retDamMaxLimSig.y, outDamPos.x2);
connect(outDamMinLimSig.y, retDamPos.x1);
connect(HeaCoi.u, retDamPos.u);
connect(TSupHeaEcoSet, uTSup.u_s);
connect(TSup, uTSup.u_m);
connect(heaCoiMinLimSig.y, HeaCoi.f1);
connect(heaCoiMaxLimSig.y, HeaCoi.f2);
connect(retDamMaxLimSig.y, HeaCoi.x1);
connect(uMaxHeaCoi.y, HeaCoi.x2);
connect(uOutDam_min, outDamPos.f2);
connect(uRetDam_min, retDamPos.f1);
connect(uRetDam_max, retDamPos.f2);
connect(Off.y, enaDis.u3);
connect(u1SupFan, enaDis.u2);
connect(HeaCoi.y, enaDis.u1);
connect(enaDis.y, yHeaCoi);
connect(uOutDam_max, outDamPos.f1);
connect(retDamPos.y, yRetDam);
connect(outDamPos.y, yOutDam);
connect(u1SupFan, uTSup.trigger);
end Modulation;