Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.Economizers.Subsequences
Subsequences for economizer control
Information
This package contains subsequences for multi zone VAV AHU economizer control.
Package Content
| Name | Description |
|---|---|
 Enable
|
Multi zone VAV AHU economizer enable/disable switch |
 Limits
|
Multi zone VAV AHU minimum outdoor air control - damper position limits |
 Modulation
|
Outdoor and return air damper position modulation sequence for multi zone VAV AHU |
 Validation
|
Collection of validation models |
Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.Economizers.Subsequences.Enable
Multi zone VAV AHU economizer enable/disable switch
Information
This is a multi zone VAV AHU economizer enable/disable sequence based on ASHRAE G36 PART 5.N.7 and PART 5.A.17. Additional conditions included in the sequence are: freeze protection (freeze protection stage 0-3, see PART 5.N.12), supply fan status (on or off, see PART 5.N.5).
The economizer is disabled whenever the outdoor air conditions exceed the economizer high limit setpoint. This sequence allows for all device types listed in ASHRAE 90.1-2013 and Title 24-2013.
In addition, the economizer gets disabled without a delay whenever any of the
following is true:
-
The supply fan is off (
uSupFan = false), -
the freeze protection stage
Buildings.Controls.OBC.ASHRAE.G36_PR1.Types.FreezeProtectionStages
is not
stage0.
The following state machine chart illustrates the transitions between enabling and disabling:
After the disable signal is activated, the following procedure is applied, per PART 5.N.7.d, in order to prevent pressure fluctuations in the HVAC system:
-
The return damper gets fully opened (
yRetDamPosMax = uRetDamPhyPosMaxandyRetDamPosMin = uRetDamPhyPosMax) forretDamFulOpeTimtime period, after which the return damper gets released to its minimum outdoor airflow control position (yRetDamPosMax = uRetDamPosMaxandyRetDamPosMin = uRetDamPosMax). -
The outdoor air damper is closed to its minimum outoor airflow control limit (
yOutDamPosMax = uOutDamPosMin) after adisDeltime delay.
This sequence also has an overwrite of the damper positions to track
a minimum mixed air temperature of TFreSet, which is
by default set to 4°C (39.2 F).
This is implemented using a proportional controller with a default deadband of
1 K, which can be adjusted using the parameter kPFrePro.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Conditional | |||
| Boolean | use_enthalpy | true | Set to true to evaluate outdoor air enthalpy in addition to temperature |
| Advanced | |||
| Hysteresis | |||
| Real | delTOutHis | 1 | Delta between the temperature hysteresis high and low limit [K] |
| Real | delEntHis | 1000 | Delta between the enthalpy hysteresis high and low limits [J/kg] |
| Delays at disable | |||
| Real | retDamFulOpeTim | 180 | Time period to keep RA damper fully open before releasing it for minimum outdoor airflow control at disable to avoid pressure fluctuations [s] |
| Real | disDel | 15 | Short time delay before closing the OA damper at disable to avoid pressure fluctuations [s] |
Connectors
| Type | Name | Description |
|---|---|---|
| input RealInput | TOut | Outdoor air temperature [K] |
| input RealInput | hOut | Outdoor air enthalpy [J/kg] |
| input RealInput | TOutCut | OA temperature high limit cutoff. For differential dry bulb temeprature condition use return air temperature measurement [K] |
| input RealInput | hOutCut | OA enthalpy high limit cutoff. For differential enthalpy use return air enthalpy measurement [J/kg] |
| input RealInput | uOutDamPosMin | Minimum outdoor air damper position, output from damper position limits sequence [1] |
| input RealInput | uOutDamPosMax | Maximum outdoor air damper position, output from damper position limits sequence [1] |
| input RealInput | uRetDamPosMax | Maximum return air damper position, output from damper position limits sequence [1] |
| input RealInput | uRetDamPosMin | Minimum return air damper position, output from damper position limits sequence [1] |
| input RealInput | uRetDamPhyPosMax | Physical maximum return air damper position, output from damper position limits sequence [1] |
| input BooleanInput | uSupFan | Supply fan on/off status signal |
| input IntegerInput | uFreProSta | Freeze protection stage status signal |
| output RealOutput | yOutDamPosMax | Maximum outdoor air damper position [1] |
| output RealOutput | yRetDamPosMin | Minimum return air damper position [1] |
| output RealOutput | yRetDamPosMax | Maximum return air damper position [1] |
Modelica definition
block Enable
"Multi zone VAV AHU economizer enable/disable switch"
parameter Boolean use_enthalpy = true
"Set to true to evaluate outdoor air enthalpy in addition to temperature";
parameter Real delTOutHis(
final unit="K",
final displayUnit="K",
final quantity="TemperatureDifference")=1
"Delta between the temperature hysteresis high and low limit";
parameter Real delEntHis(
final unit="J/kg",
final quantity="SpecificEnergy")=1000
"Delta between the enthalpy hysteresis high and low limits";
parameter Real retDamFulOpeTim(
final unit="s",
final quantity="Time")=180
"Time period to keep RA damper fully open before releasing it for minimum outdoor airflow control
at disable to avoid pressure fluctuations";
parameter Real disDel(
final unit="s",
final quantity="Time")=15
"Short time delay before closing the OA damper at disable to avoid pressure fluctuations";
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 hOut(
final unit="J/kg",
final quantity="SpecificEnergy") if use_enthalpy
"Outdoor air enthalpy";
Buildings.Controls.OBC.CDL.Interfaces.RealInput TOutCut(
final unit="K",
final displayUnit="degC",
final quantity = "ThermodynamicTemperature")
"OA temperature high limit cutoff. For differential dry bulb temeprature condition use return air temperature measurement";
Buildings.Controls.OBC.CDL.Interfaces.RealInput hOutCut(
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.RealInput uOutDamPosMin(
final unit="1",
final min=0,
final max=1)
"Minimum outdoor air damper position, output from damper position limits sequence";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uOutDamPosMax(
final unit="1",
final min=0,
final max=1)
"Maximum outdoor air damper position, output from damper position limits sequence";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uRetDamPosMax(
final unit="1",
final min=0,
final max=1)
"Maximum return air damper position, output from damper position limits sequence";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uRetDamPosMin(
final unit="1",
final min=0,
final max=1)
"Minimum return air damper position, output from damper position limits sequence";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uRetDamPhyPosMax(
final unit="1",
final min=0,
final max=1)
"Physical maximum return air damper position, output from damper position limits sequence";
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput uSupFan
"Supply fan on/off status signal";
Buildings.Controls.OBC.CDL.Interfaces.IntegerInput uFreProSta "Freeze protection stage status signal";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yOutDamPosMax(
final unit="1",
final min=0,
final max=1) "Maximum outdoor air damper position";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yRetDamPosMin(
final unit="1",
final min=0,
final max=1) "Minimum return air damper position";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yRetDamPosMax(
final unit="1",
final min=0,
final max=1) "Maximum return air damper position";
Buildings.Controls.OBC.CDL.Logical.TrueFalseHold truFalHol(
trueHoldDuration=600) "10 min on/off delay";
Buildings.Controls.OBC.CDL.Logical.And andEnaDis
"Logical and that checks freeze protection stage and zone state";
protected
final parameter Real TOutHigLimCutHig(
final unit="K",
final displayUnit="K",
final quantity="TemperatureDifference")= 0
"Hysteresis high limit cutoff";
final parameter Real TOutHigLimCutLow = TOutHigLimCutHig - delTOutHis
"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 - delEntHis
"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.Subtract sub2
if use_enthalpy "Add block determines difference between hOut and hOutCut";
Buildings.Controls.OBC.CDL.Continuous.Subtract sub1
"Add block determines difference between TOut and TOutCut";
Buildings.Controls.OBC.CDL.Continuous.Hysteresis hysOutTem(
final uLow=TOutHigLimCutLow,
final uHigh=TOutHigLimCutHig)
"Outdoor air temperature hysteresis for both fixed and 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 both fixed and differential enthalpy cutoff conditions";
Buildings.Controls.OBC.CDL.Continuous.Switch outDamSwitch
"Set maximum OA damper position to minimum at disable (after a given time delay)";
Buildings.Controls.OBC.CDL.Continuous.Switch retDamSwitch "Set minimum RA damper position to maximum at disable";
Buildings.Controls.OBC.CDL.Continuous.Switch maxRetDamSwitch
"Keep maximum RA damper position at physical maximum for a short time period after disable signal";
Buildings.Controls.OBC.CDL.Continuous.Switch minRetDamSwitch
"Keep minimum RA damper position at physical maximum for a short time period after disable";
Buildings.Controls.OBC.CDL.Logical.Nor nor1 "Logical nor";
Buildings.Controls.OBC.CDL.Logical.Not not2 "Logical not that starts the timer at disable signal ";
Buildings.Controls.OBC.CDL.Logical.And and2 "Logical and";
Buildings.Controls.OBC.CDL.Logical.And and1 "Logical and checks supply fan status";
Buildings.Controls.OBC.CDL.Logical.And and3 "Logical and which checks supply fan status";
Buildings.Controls.OBC.CDL.Integers.Equal intEqu
"Logical block to check if the freeze protection is deactivated";
Buildings.Controls.OBC.CDL.Logical.TrueDelay delOutDamOsc(
final delayTime=disDel)
"Small delay before closing the outdoor air damper to avoid pressure fluctuations";
Buildings.Controls.OBC.CDL.Logical.TrueDelay delRetDam(
final delayTime=retDamFulOpeTim)
"Keep return damper open to its physical maximum for a short period of time before closing the outdoor air damper and resuming the maximum return air damper position, per G36 Part N7";
Buildings.Controls.OBC.CDL.Logical.Not not1 "Logical not";
Buildings.Controls.OBC.CDL.Integers.Sources.Constant conInt(
final k=Buildings.Controls.OBC.ASHRAE.G36_PR1.Types.FreezeProtectionStages.stage0)
"Integer constant, stage 0";
equation
connect(TOut, sub1.u1);
connect(TOutCut, sub1.u2);
connect(sub1.y, hysOutTem.u);
connect(hOut, sub2.u1);
connect(hOutCut, sub2.u2);
connect(sub2.y, hysOutEnt.u);
connect(hysOutTem.y, nor1.u1);
connect(hysOutEnt.y, nor1.u2);
connect(entSubst.y, nor1.u2);
connect(uOutDamPosMin, outDamSwitch.u1);
connect(uOutDamPosMax, outDamSwitch.u3);
connect(uRetDamPhyPosMax, maxRetDamSwitch.u1);
connect(uRetDamPosMax, maxRetDamSwitch.u3);
connect(nor1.y, truFalHol.u);
connect(andEnaDis.y, not2.u);
connect(maxRetDamSwitch.y, yRetDamPosMax);
connect(and2.y, maxRetDamSwitch.u2);
connect(and2.y, minRetDamSwitch.u2);
connect(not2.y, retDamSwitch.u2);
connect(uRetDamPosMax, retDamSwitch.u1);
connect(uRetDamPosMin, retDamSwitch.u3);
connect(retDamSwitch.y, minRetDamSwitch.u3);
connect(uRetDamPhyPosMax, minRetDamSwitch.u1);
connect(truFalHol.y, and1.u1);
connect(and1.y, andEnaDis.u1);
connect(uSupFan, and1.u2);
connect(outDamSwitch.u2, and3.y);
connect(not2.y, and3.u1);
connect(and2.u1, not2.y);
connect(and3.u2, delOutDamOsc.y);
connect(delOutDamOsc.u, not2.y);
connect(not2.y, delRetDam.u);
connect(delRetDam.y, not1.u);
connect(not1.y, and2.u2);
connect(uFreProSta, intEqu.u1);
connect(conInt.y, intEqu.u2);
connect(intEqu.y, andEnaDis.u2);
connect(outDamSwitch.y, yOutDamPosMax);
connect(minRetDamSwitch.y, yRetDamPosMin);
end Enable;
Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.Economizers.Subsequences.Limits
Multi zone VAV AHU minimum outdoor air control - damper position limits
Information
This block models the multi zone VAV AHU minimum outdoor air control with a single common damper for minimum outdoor air and economizer functions based on outdoor airflow measurement, designed in line with ASHRAE Guidline 36 (G36), PART 5.N.6.c.
The controller is enabled when the supply fan is proven on (uSupFan=true),
the AHU operation mode
Buildings.Controls.OBC.ASHRAE.G36_PR1.Types.OperationModes equals occupied,
and the freeze protection stage
Buildings.Controls.OBC.ASHRAE.G36_PR1.Types.FreezeProtectionStages is stage1 or lower.
Otherwise the damper position limits are set to their corresponding maximum and minimum physical or at
commissioning fixed limits. The state machine chart below illustrates listed conditions:
The controller sets the outdoor and return damper position limits so
that the outdoor airflow rate VOut_flow stays equal or above the
minimum outdoor air setpoint VOutMinSet_flow. The fraction of the controller
output signal between yMin and uRetDamMin is
linearly mapped to the outdoor air damper minimal position yOutDamPosMin
while the fraction of the controller output between uRetDamMin and
yMax is linearly mapped to the return air damper maximum position
yRetDamPosMax. Thus the dampers are not interlocked.
The following control charts show the input/output structure and an expected damper position limits for a well configured controller.
The expected damper position limits vs. the control loop signal are as follows:
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Controller | |||
| SimpleController | controllerType | Buildings.Controls.OBC.CDL.T... | Type of controller |
| Real | k | 0.05 | Gain of damper limit controller [1] |
| Real | Ti | 120 | Time constant of damper limit controller integrator block [s] |
| Real | Td | 0.1 | Time constant of damper limit controller derivative block [s] |
| Commissioning | |||
| Controller | |||
| Real | uRetDamMin | 0.5 | Loop signal value to start decreasing the maximum return air damper position [1] |
| Physical damper position limits | |||
| Real | retDamPhyPosMax | 1 | Physically fixed maximum position of the return air damper [1] |
| Real | retDamPhyPosMin | 0 | Physically fixed minimum position of the return air damper [1] |
| Real | outDamPhyPosMax | 1 | Physically fixed maximum position of the outdoor air damper [1] |
| Real | outDamPhyPosMin | 0 | Physically fixed minimum position of the outdoor air damper [1] |
Connectors
| Type | Name | Description |
|---|---|---|
| input RealInput | VOut_flow_normalized | Measured outdoor volumetric airflow rate, normalized by design minimum outdoor airflow rate [1] |
| input RealInput | VOutMinSet_flow_normalized | Effective minimum outdoor airflow setpoint, normalized by design minimum outdoor airflow rate [1] |
| input IntegerInput | uOpeMod | AHU operation mode status signal |
| input IntegerInput | uFreProSta | Freeze protection status signal |
| input BooleanInput | uSupFan | Supply fan status signal |
| output RealOutput | yOutDamPosMin | Minimum outdoor air damper position limit [1] |
| output RealOutput | yOutDamPosMax | Maximum outdoor air damper position limit [1] |
| output RealOutput | yRetDamPosMin | Minimum return air damper position limit [1] |
| output RealOutput | yRetDamPosMax | Maximum return air damper position limit [1] |
| output RealOutput | yRetDamPhyPosMax | Physical maximum return air damper position limit. Required as an input for the economizer enable disable sequence [1] |
Modelica definition
block Limits
"Multi zone VAV AHU minimum outdoor air control - damper position limits"
parameter Real uRetDamMin(
final min=yMin,
final max=yMax,
final unit="1") = 0.5
"Loop signal value to start decreasing the maximum return air damper position";
parameter Buildings.Controls.OBC.CDL.Types.SimpleController controllerType=
Buildings.Controls.OBC.CDL.Types.SimpleController.PI
"Type of controller";
parameter Real k(
final unit="1")=0.05 "Gain of damper limit controller";
parameter Real Ti(
final unit="s",
final quantity="Time")=120
"Time constant of damper limit controller integrator block";
parameter Real Td(
final unit="s",
final quantity="Time")=0.1
"Time constant of damper limit controller derivative block";
parameter Real retDamPhyPosMax(
final min=0,
final max=1,
final unit="1") = 1 "Physically fixed maximum position of the return air damper";
parameter Real retDamPhyPosMin(
final min=0,
final max=1,
final unit="1") = 0
"Physically fixed minimum position of the return air damper";
parameter Real outDamPhyPosMax(
final min=0,
final max=1,
final unit="1") = 1
"Physically fixed maximum position of the outdoor air damper";
parameter Real outDamPhyPosMin(
final min=0,
final max=1,
final unit="1") = 0
"Physically fixed minimum position of the outdoor air damper";
Buildings.Controls.OBC.CDL.Interfaces.RealInput VOut_flow_normalized(
final unit="1")
"Measured outdoor volumetric airflow rate, normalized by design minimum outdoor airflow rate";
Buildings.Controls.OBC.CDL.Interfaces.RealInput VOutMinSet_flow_normalized(
final unit="1")
"Effective minimum outdoor airflow setpoint, normalized by design minimum outdoor airflow rate";
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 uSupFan
"Supply fan status signal";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yOutDamPosMin(
final min=outDamPhyPosMin,
final max=outDamPhyPosMax,
final unit="1") "Minimum outdoor air damper position limit";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yOutDamPosMax(
final min=outDamPhyPosMin,
final max=outDamPhyPosMax,
final unit="1") "Maximum outdoor air damper position limit";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yRetDamPosMin(
final min=retDamPhyPosMin,
final max=retDamPhyPosMax,
final unit="1") "Minimum return air damper position limit";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yRetDamPosMax(
final min=retDamPhyPosMin,
final max=retDamPhyPosMax,
final unit="1") "Maximum return air damper position limit";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yRetDamPhyPosMax(
final min=0,
final max=1,
final unit="1")
"Physical maximum return air damper position limit. Required as an input for the economizer enable disable sequence";
Buildings.Controls.OBC.CDL.Continuous.PIDWithReset damLimCon(
final controllerType=controllerType,
final k=k,
final Ti=Ti,
final Td=Td,
final yMax=yMax,
final yMin=yMin)
"Damper position limit controller";
protected
parameter Real yMin=0 "Lower limit of control loop signal";
parameter Real yMax=1 "Upper limit of control loop signal";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant outDamPhyPosMinSig(
final k=outDamPhyPosMin)
"Physically fixed minimum position of the outdoor air damper. This is the initial position of the economizer damper";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant outDamPhyPosMaxSig(
final k=outDamPhyPosMax)
"Physically fixed maximum position of the outdoor air damper.";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant retDamPhyPosMinSig(
final k=retDamPhyPosMin)
"Physically fixed minimum position of the return air damper";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant retDamPhyPosMaxSig(
final k=retDamPhyPosMax)
"Physically fixed maximum position of the return air damper. This is the initial condition of the return air damper";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant minSigLim(
final k=yMin)
"Equals minimum controller output signal";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant maxSigLim(
final k=yMax)
"Equals maximum controller output signal";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant sigFraForOutDam(
final k=uRetDamMin) "Equals the fraction of the control loop signal below which the outdoor air damper
limit gets modulated and above which the return air damper limit gets modulated";
Buildings.Controls.OBC.CDL.Continuous.Line minOutDam(
final limitBelow=true,
final limitAbove=true)
"Linear mapping of the outdoor air damper position to the control signal";
Buildings.Controls.OBC.CDL.Continuous.Line minRetDam(
final limitBelow=true,
final limitAbove=true)
"Linear mapping of the return air damper position to the control signal";
Buildings.Controls.OBC.CDL.Continuous.Switch retDamPosMinSwitch
"A switch to deactivate the return air damper minimal outdoor airflow control";
Buildings.Controls.OBC.CDL.Continuous.Switch outDamPosMaxSwitch
"A switch to deactivate the outdoor air damper minimal outdoor airflow control";
Buildings.Controls.OBC.CDL.Logical.Not not1 "Logical not block";
Buildings.Controls.OBC.CDL.Integers.Sources.Constant conInt(
final k=Buildings.Controls.OBC.ASHRAE.G36_PR1.Types.FreezeProtectionStages.stage1)
"Freeze protection stage 1";
Buildings.Controls.OBC.CDL.Integers.Sources.Constant conInt1(
final k=Buildings.Controls.OBC.ASHRAE.G36_PR1.Types.OperationModes.occupied)
"Occupied mode index";
Buildings.Controls.OBC.CDL.Integers.LessEqual intLesEqu
"Check if freeze protection stage is stage 0";
Buildings.Controls.OBC.CDL.Integers.Equal intEqu
"Check if operation mode is occupied";
Buildings.Controls.OBC.CDL.Logical.And and2 "Logical and";
Buildings.Controls.OBC.CDL.Logical.And and3 "Logical and";
equation
connect(minRetDam.y, yRetDamPosMax);
connect(retDamPosMinSwitch.y, minRetDam.f2);
connect(sigFraForOutDam.y, minRetDam.x1);
connect(maxSigLim.y, minRetDam.x2);
connect(VOut_flow_normalized, damLimCon.u_m);
connect(VOutMinSet_flow_normalized, damLimCon.u_s);
connect(damLimCon.y, minRetDam.u);
connect(outDamPosMaxSwitch.y, minOutDam.f2);
connect(minSigLim.y, minOutDam.x1);
connect(sigFraForOutDam.y, minOutDam.x2);
connect(damLimCon.y, minOutDam.u);
connect(outDamPosMaxSwitch.y, yOutDamPosMax);
connect(minOutDam.y, yOutDamPosMin);
connect(retDamPhyPosMaxSig.y, retDamPosMinSwitch.u1);
connect(retDamPhyPosMaxSig.y, minRetDam.f1);
connect(retDamPhyPosMinSig.y, retDamPosMinSwitch.u3);
connect(outDamPhyPosMaxSig.y, outDamPosMaxSwitch.u3);
connect(outDamPhyPosMinSig.y, outDamPosMaxSwitch.u1);
connect(outDamPhyPosMinSig.y, minOutDam.f1);
connect(not1.y, retDamPosMinSwitch.u2);
connect(not1.y, outDamPosMaxSwitch.u2);
connect(retDamPosMinSwitch.y, yRetDamPosMin);
connect(retDamPhyPosMaxSig.y, yRetDamPhyPosMax);
connect(uOpeMod, intEqu.u1);
connect(conInt1.y, intEqu.u2);
connect(conInt.y, intLesEqu.u2);
connect(uFreProSta, intLesEqu.u1);
connect(damLimCon.trigger, uSupFan);
connect(uSupFan, and2.u1);
connect(intLesEqu.y, and2.u2);
connect(and2.y, and3.u1);
connect(and3.y, not1.u);
connect(intEqu.y, and3.u2);
end Limits;
Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.Economizers.Subsequences.Modulation
Outdoor and return air damper position modulation sequence for multi zone VAV AHU
Information
This is a multi zone VAV AHU economizer modulation block. It calculates the outdoor and return air damper positions based on the supply air temperature control loop signal. The implementation is in line with ASHRAE Guidline 36 (G36), PART 5.N.2.c. Damper positions are linearly mapped to the supply air control loop signal. This is a final sequence in the composite multi 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_PR1.AHUs.MultiZone.VAV.Economizers.Subsequences.Limits and Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.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 control charts below show the input-output structure and an economizer damper modulation sequence assuming a well configured controller. Control diagram:
Multi zone AHU economizer modulation control chart:
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Commissioning | |||
| Controller | |||
| Real | uMin | -0.25 | Lower limit of controller input when outdoor damper opens (see diagram) [1] |
| Real | uMax | +0.25 | Upper limit of controller input when return damper is closed (see diagram) [1] |
| Real | uOutDamMax | (uMin + uMax)/2 | Maximum loop signal for the OA damper to be fully open [1] |
| Real | uRetDamMin | (uMin + uMax)/2 | Minimum loop signal for the RA damper to be fully open [1] |
Connectors
| Type | Name | Description |
|---|---|---|
| input RealInput | uTSup | Signal for supply air temperature control (T Sup Control Loop Signal in diagram) [1] |
| input RealInput | uOutDamPosMin | Minimum economizer damper position limit as returned by the damper position limits sequence [1] |
| input RealInput | uOutDamPosMax | 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 | uRetDamPosMin | Minimum return air damper position limit as returned by the economizer enable-disable sequence [1] |
| input RealInput | uRetDamPosMax | Maximum return air damper position limit as returned by the economizer enable-disable sequence [1] |
| output RealOutput | yOutDamPos | Economizer damper position [1] |
| output RealOutput | yRetDamPos | Return air damper position [1] |
Modelica definition
block Modulation
"Outdoor and return air damper position modulation sequence for multi zone VAV AHU"
parameter Real uMin(
final max=0,
final unit="1")=-0.25
"Lower limit of controller input when outdoor damper opens (see diagram)";
parameter Real uMax(
final min=0,
final unit="1")=+0.25
"Upper limit of controller input when return damper is closed (see diagram)";
parameter Real uOutDamMax(
final min=-1,
final max=1,
final unit="1") = (uMin + uMax)/2
"Maximum loop signal for the OA damper to be fully open";
parameter Real uRetDamMin(
final min=-1,
final max=1,
final unit="1") = (uMin + uMax)/2
"Minimum loop signal for the RA damper to be fully open";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uTSup(final unit="1")
"Signal for supply air temperature control (T Sup Control Loop Signal in diagram)";
Buildings.Controls.OBC.CDL.Interfaces.RealInput uOutDamPosMin(
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 uOutDamPosMax(
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 uRetDamPosMin(
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 uRetDamPosMax(
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 yOutDamPos(
final min=0,
final max=1,
final unit="1") "Economizer damper position";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yRetDamPos(
final min=0,
final max=1,
final unit="1") "Return air damper position";
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 outDamMaxLimSig(
final k=uOutDamMax) "Maximum control loop signal for the outdoor air damper";
Buildings.Controls.OBC.CDL.Continuous.Sources.Constant retDamConMinLimSig(
final k=uRetDamMin)
"Minimal control loop signal for the return 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.Min min "Overwrite due to freeze protection";
Buildings.Controls.OBC.CDL.Continuous.Max max "Overwrite due to freeze protection";
equation
connect(outDamPos.x2, outDamMaxLimSig.y);
connect(outDamPos.x1, outDamMinLimSig.y);
connect(outDamPos.f1, uOutDamPosMin);
connect(outDamPos.f2, uOutDamPosMax);
connect(retDamPos.x2, retDamMaxLimSig.y);
connect(retDamPos.x1, retDamConMinLimSig.y);
connect(retDamPos.f1, uRetDamPosMax);
connect(retDamPos.f2, uRetDamPosMin);
connect(min.u2, uOutDamPosMax);
connect(min.u1, outDamPos.y);
connect(max.u1, retDamPos.y);
connect(uRetDamPosMin, max.u2);
connect(uTSup, retDamPos.u);
connect(uTSup, outDamPos.u);
connect(yOutDamPos, min.y);
connect(max.y, yRetDamPos);
end Modulation;