Buildings.Controls.OBC.ASHRAE.G36.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
|
Package of sequences to calculate the damper position limits of the economizer |
| Modulations
|
Package of sequences to modulate economizer dampers |
 Validation
|
Collection of validation models |
Buildings.Controls.OBC.ASHRAE.G36.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 the Section 5.16.7 of the ASHRAE Guideline 36, May 2020. Additional conditions included in the sequence are: freeze protection (freeze protection stage 0-3, see Section 5.16.12), supply fan status (on or off, see Section 5.16.5).
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 (
u1SupFan = false), -
the freeze protection stage
Buildings.Controls.OBC.ASHRAE.G36.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, in order to prevent pressure fluctuations in the HVAC system:
-
The return damper gets fully opened (
yRetDam_max = uRetDamPhy_maxandyRetDam_min = uRetDamPhy_max) forretDamFulOpeTimtime period, after which the return damper gets released to its minimum outdoor airflow control position (yRetDam_max = uRetDam_maxandyRetDam_min = uRetDam_max). -
The outdoor air damper is closed to its minimum outoor airflow control limit (
yOutDam_max = uOutDam_min) after adisDeltime delay.
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 | 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 temperature 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 | uOutDam_min | Minimum outdoor air damper position, output from damper position limits sequence [1] |
| input RealInput | uOutDam_max | Maximum outdoor air damper position, output from damper position limits sequence [1] |
| input RealInput | uRetDam_max | Maximum return air damper position, output from damper position limits sequence [1] |
| input RealInput | uRetDam_min | Minimum return air damper position, output from damper position limits sequence [1] |
| input RealInput | uRetDamPhy_max | Physical maximum return air damper position, output from damper position limits sequence [1] |
| input BooleanInput | u1SupFan | Supply fan proven on |
| input IntegerInput | uFreProSta | Freeze protection stage status signal |
| output RealOutput | yOutDam_max | Maximum outdoor air damper position [1] |
| output RealOutput | yRetDam_min | Minimum return air damper position [1] |
| output RealOutput | yRetDam_max | 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 (OA) 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 temperature 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 uOutDam_min(
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 uOutDam_max(
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 uRetDam_max(
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 uRetDam_min(
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 uRetDamPhy_max(
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 u1SupFan
"Supply fan proven on";
Buildings.Controls.OBC.CDL.Interfaces.IntegerInput uFreProSta "Freeze protection stage status signal";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yOutDam_max(
final unit="1",
final min=0,
final max=1)
"Maximum outdoor air damper position";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yRetDam_min(
final unit="1",
final min=0,
final max=1)
"Minimum return air damper position";
Buildings.Controls.OBC.CDL.Interfaces.RealOutput yRetDam_max(
final unit="1",
final min=0,
final max=1)
"Maximum return air damper position";
Buildings.Controls.OBC.CDL.Logical.TrueFalseHold truFalHol(
final trueHoldDuration=600)
"Economizer should not be enabled or disabled within 10 minutes of change";
Buildings.Controls.OBC.CDL.Logical.And andEnaDis
"Check 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.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.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 "Check supply fan status";
Buildings.Controls.OBC.CDL.Logical.And and3
"Check if delay time has been passed after economizer being disabled";
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.Types.FreezeProtectionStages.stage0)
"Integer constant, stage 0";
Buildings.Controls.OBC.CDL.Logical.Sources.Constant entSubst1(
final k=false) if not use_enthalpy
"Deactivates outdoor air enthalpy condition if there is no enthalpy sensor";
Buildings.Controls.OBC.CDL.Logical.Or or2
"Check if either the temperature or the enthalpy condition is satisfied";
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(uOutDam_min, outDamSwitch.u1);
connect(uOutDam_max, outDamSwitch.u3);
connect(uRetDamPhy_max, maxRetDamSwitch.u1);
connect(uRetDam_max, maxRetDamSwitch.u3);
connect(andEnaDis.y, not2.u);
connect(maxRetDamSwitch.y, yRetDam_max);
connect(and2.y, maxRetDamSwitch.u2);
connect(and2.y, minRetDamSwitch.u2);
connect(not2.y, retDamSwitch.u2);
connect(uRetDam_max, retDamSwitch.u1);
connect(uRetDam_min, retDamSwitch.u3);
connect(retDamSwitch.y, minRetDamSwitch.u3);
connect(uRetDamPhy_max, minRetDamSwitch.u1);
connect(truFalHol.y, and1.u1);
connect(and1.y, andEnaDis.u1);
connect(u1SupFan, 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, yOutDam_max);
connect(minRetDamSwitch.y, yRetDam_min);
connect(or2.y, truFalHol.u);
connect(hysOutTem.y, or2.u1);
connect(hysOutEnt.y, or2.u2);
connect(entSubst1.y, or2.u2);
end Enable;