Buildings.DHC.Plants.Cooling.Subsystems
Package of models for subsystems of cooling plants
Information
This package contains models for subsystems composing central cooling plants.
Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).
Package Content
| Name | Description |
|---|---|
 CoolingTowersParallel
|
Multiple identical cooling towers in parallel connection |
 CoolingTowersWithBypass
|
Cooling tower system with bypass valve |
 Examples
|
Example models integrating multiple components |
Buildings.DHC.Plants.Cooling.Subsystems.CoolingTowersParallel
Multiple identical cooling towers in parallel connection
Information
This model implements a parallel cooling tower system with num
identical cooling towers.
The cooling tower type is replaceable. Buildings.Fluid.HeatExchangers.CoolingTowers.Merkel is currently used in this model.
Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model with two ports and declaration of quantities that are used by many models).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | PartialMedium | Medium in the component | |
| Integer | num | 2 | Number of cooling towers |
| PressureDifference | dpValve_nominal | Nominal pressure difference of the valve [Pa] | |
| Merkel | cooTow[num] | cooTow(each final allowFlowR... | Cooling tower type |
| Nominal condition | |||
| MassFlowRate | m_flow_nominal | Nominal mass flow rate [kg/s] | |
| PressureDifference | dp_nominal | Nominal pressure difference of the tower [Pa] | |
| Real | ratWatAir_nominal | 0.625 | Design water-to-air ratio [1] |
| Heat transfer | |||
| Temperature | TAirInWB_nominal | Nominal outdoor (air inlet) wetbulb temperature [K] | |
| Temperature | TWatIn_nominal | Nominal water inlet temperature [K] | |
| TemperatureDifference | dT_nominal | Temperature difference between inlet and outlet of the tower [K] | |
| Fan | |||
| Power | PFan_nominal | Fan power [W] | |
| Assumptions | |||
| Boolean | allowFlowReversal | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Advanced | |||
| MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s] |
| Diagnostics | |||
| Boolean | show_T | false | = true, if actual temperature at port is computed |
| Dynamics | |||
| Conservation equations | |||
| Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Type of energy balance: dynamic (3 initialization options) or steady state |
| Filtered opening | |||
| Boolean | use_inputFilter | true | = true, if opening is filtered with a 2nd order CriticalDamping filter |
Connectors
| Type | Name | Description |
|---|---|---|
| replaceable package Medium | Medium in the component | |
| FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b) |
| FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b) |
| input BooleanInput | on[num] | On signal for cooling towers |
| input RealInput | uFanSpe | Fan speed control signal [1] |
| input RealInput | TWetBul | Entering air wetbulb temperature [K] |
| output RealOutput | PFan[num] | Electric power consumed by fan [W] |
| output RealOutput | TLvg | Leaving water temperature [K] |
Modelica definition
model CoolingTowersParallel
"Multiple identical cooling towers in parallel connection"
extends Buildings.Fluid.Interfaces.PartialTwoPortInterface(
redeclare replaceable package Medium=Buildings.Media.Water);
parameter Integer num(
final min=1)=2
"Number of cooling towers";
parameter Modelica.Fluid.Types.Dynamics energyDynamics=Modelica.Fluid.Types.Dynamics.FixedInitial
"Type of energy balance: dynamic (3 initialization options) or steady state";
parameter Modelica.Units.SI.PressureDifference dp_nominal
"Nominal pressure difference of the tower";
parameter Modelica.Units.SI.PressureDifference dpValve_nominal
"Nominal pressure difference of the valve";
parameter Real ratWatAir_nominal(
final min=0,
final unit="1")=0.625
"Design water-to-air ratio";
parameter Modelica.Units.SI.Temperature TAirInWB_nominal
"Nominal outdoor (air inlet) wetbulb temperature";
parameter Modelica.Units.SI.Temperature TWatIn_nominal
"Nominal water inlet temperature";
parameter Modelica.Units.SI.TemperatureDifference dT_nominal
"Temperature difference between inlet and outlet of the tower";
parameter Modelica.Units.SI.Power PFan_nominal "Fan power";
parameter Boolean use_inputFilter=true
"= true, if opening is filtered with a 2nd order CriticalDamping filter";
Modelica.Blocks.Interfaces.BooleanInput on[num]
"On signal for cooling towers";
Modelica.Blocks.Interfaces.RealInput uFanSpe(
final unit="1")
"Fan speed control signal";
Modelica.Blocks.Interfaces.RealInput TWetBul(
final unit="K",
displayUnit="degC")
"Entering air wetbulb temperature";
Modelica.Blocks.Interfaces.RealOutput PFan[num](
each final quantity="Power",
each final unit="W")
"Electric power consumed by fan";
Modelica.Blocks.Interfaces.RealOutput TLvg(
final unit="K",
displayUnit="degC")
"Leaving water temperature";
replaceable Buildings.Fluid.HeatExchangers.CoolingTowers.Merkel cooTow[num](
each final allowFlowReversal=allowFlowReversal,
each final m_flow_small=m_flow_small,
each final ratWatAir_nominal=ratWatAir_nominal,
each final TAirInWB_nominal=TAirInWB_nominal,
each final TWatIn_nominal=TWatIn_nominal,
each final TWatOut_nominal=TWatIn_nominal-dT_nominal,
each final PFan_nominal=PFan_nominal,
each final dp_nominal=0)
constrainedby Buildings.Fluid.HeatExchangers.CoolingTowers.BaseClasses.CoolingTowerVariableSpeed
( redeclare each final package Medium=Medium,
each final show_T=show_T,
each final m_flow_nominal=m_flow_nominal,
each final energyDynamics=energyDynamics)
"Cooling tower type";
Buildings.Fluid.Actuators.Valves.TwoWayEqualPercentage val[num](
redeclare each final package Medium=Medium,
each final allowFlowReversal=allowFlowReversal,
each final m_flow_nominal=m_flow_nominal,
each final dpValve_nominal=dpValve_nominal,
each final use_inputFilter=use_inputFilter,
each riseTime=30,
each final dpFixed_nominal=dp_nominal)
"Cooling tower valves";
Buildings.Controls.OBC.CDL.Conversions.BooleanToReal booToRea[num]
"Boolean signal to real signal";
Buildings.Fluid.Sensors.TemperatureTwoPort senTem(
redeclare final package Medium=Medium,
final allowFlowReversal=allowFlowReversal,
final m_flow_nominal=m_flow_nominal,
final m_flow_small=m_flow_small,
final T_start=Medium.T_default);
equation
for i in 1:num loop
connect(port_a,val[i].port_a);
connect(val[i].port_b,cooTow[i].port_a);
connect(uFanSpe,cooTow[i].y);
connect(TWetBul,cooTow[i].TAir);
connect(cooTow[i].PFan,PFan[i]);
connect(cooTow[i].port_b, senTem.port_a);
end for;
connect(on,booToRea.u);
connect(senTem.port_b, port_b);
connect(senTem.T, TLvg);
connect(booToRea.y, val.y);
end CoolingTowersParallel;
Buildings.DHC.Plants.Cooling.Subsystems.CoolingTowersWithBypass
Cooling tower system with bypass valve
Information
This model simulates parallel connected cooling tower subsystem with a bypass valve.
The bypass valve is controlled to enforce that the leaving condenser water
temperature does not drop below the minimum temperature TMin.
By default, the condenser water setpoint is the ambient wet bulb temperature
TWetBul plus the approach temperature dTApp.
Inside the model, a cooling tower fan speed controller is also implemented to maintain the condenser water at its setpoint.
Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model with two ports and declaration of quantities that are used by many models).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | PartialMedium | Medium in the component | |
| Integer | num | 2 | Number of cooling towers |
| PressureDifference | dpValve_nominal | Nominal pressure difference of the valve [Pa] | |
| Nominal condition | |||
| MassFlowRate | m_flow_nominal | Nominal mass flow rate [kg/s] | |
| Pressure | dp_nominal | Nominal pressure difference of the tower [Pa] | |
| Real | ratWatAir_nominal | 0.625 | Design water-to-air ratio [1] |
| Heat transfer | |||
| Temperature | TAirInWB_nominal | Nominal outdoor (air inlet) wetbulb temperature [K] | |
| Temperature | TWatIn_nominal | Nominal water inlet temperature [K] | |
| TemperatureDifference | dT_nominal | Temperature difference between inlet and outlet of the tower [K] | |
| Fan | |||
| Power | PFan_nominal | Fan power [W] | |
| Control Settings | |||
| TemperatureDifference | dTApp | 3 | Approach temperature [K] |
| Temperature | TMin | Minimum allowed water temperature entering chiller [K] | |
| SimpleController | controllerType | Modelica.Blocks.Types.Simple... | Type of fan speed controller |
| Real | k | 1 | Gain of the tower PID controller [1] |
| Time | Ti | 60 | Integrator time constant of the tower PID controller [s] |
| Time | Td | 0.1 | Derivative time constant of the tower PID controller [s] |
| Assumptions | |||
| Boolean | allowFlowReversal | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Advanced | |||
| MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s] |
| Diagnostics | |||
| Boolean | show_T | false | = true, if actual temperature at port is computed |
| Dynamics | |||
| Conservation equations | |||
| Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Type of energy balance: dynamic (3 initialization options) or steady state |
| Filtered opening | |||
| Boolean | use_inputFilter | true | = true, if opening is filtered with a 2nd order CriticalDamping filter |
| Time | riseTime | 30 | Pump rise time of the filter (time to reach 99.6 % of the speed) [s] |
Connectors
| Type | Name | Description |
|---|---|---|
| replaceable package Medium | Medium in the component | |
| FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b) |
| FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b) |
| input BooleanInput | on[num] | On signal for cooling towers |
| input RealInput | TWetBul | Entering air wetbulb temperature [K] |
| output RealOutput | PFan[num] | Electric power consumed by fan [W] |
| output RealOutput | TLvg | Leaving water temperature [K] |
Modelica definition
model CoolingTowersWithBypass
"Cooling tower system with bypass valve"
extends Buildings.Fluid.Interfaces.PartialTwoPortInterface(
redeclare replaceable package Medium=Buildings.Media.Water);
parameter Integer num(
final min=1)=2
"Number of cooling towers";
parameter Modelica.Fluid.Types.Dynamics energyDynamics=Modelica.Fluid.Types.Dynamics.FixedInitial
"Type of energy balance: dynamic (3 initialization options) or steady state";
parameter Boolean use_inputFilter=true
"= true, if opening is filtered with a 2nd order CriticalDamping filter";
parameter Modelica.Units.SI.Time riseTime=30
"Pump rise time of the filter (time to reach 99.6 % of the speed)";
parameter Modelica.Units.SI.Pressure dp_nominal
"Nominal pressure difference of the tower";
parameter Modelica.Units.SI.PressureDifference dpValve_nominal
"Nominal pressure difference of the valve";
parameter Real ratWatAir_nominal(
final min=0,
final unit="1")=0.625
"Design water-to-air ratio";
parameter Modelica.Units.SI.Temperature TAirInWB_nominal
"Nominal outdoor (air inlet) wetbulb temperature";
parameter Modelica.Units.SI.Temperature TWatIn_nominal
"Nominal water inlet temperature";
parameter Modelica.Units.SI.TemperatureDifference dT_nominal
"Temperature difference between inlet and outlet of the tower";
parameter Modelica.Units.SI.Power PFan_nominal "Fan power";
parameter Modelica.Units.SI.TemperatureDifference dTApp=3
"Approach temperature";
parameter Modelica.Units.SI.Temperature TMin
"Minimum allowed water temperature entering chiller";
parameter Modelica.Blocks.Types.SimpleController controllerType=Modelica.Blocks.Types.SimpleController.PI
"Type of fan speed controller";
parameter Real k(
final unit="1",
final min=0)=1
"Gain of the tower PID controller";
parameter Modelica.Units.SI.Time Ti(final min=Modelica.Constants.small) = 60
"Integrator time constant of the tower PID controller";
parameter Modelica.Units.SI.Time Td(final min=0) = 0.1
"Derivative time constant of the tower PID controller";
Modelica.Blocks.Interfaces.BooleanInput on[num]
"On signal for cooling towers";
Modelica.Blocks.Interfaces.RealInput TWetBul(
final unit="K",
displayUnit="degC")
"Entering air wetbulb temperature";
Modelica.Blocks.Interfaces.RealOutput PFan[num](
each final quantity="Power",
each final unit="W")
"Electric power consumed by fan";
Modelica.Blocks.Interfaces.RealOutput TLvg(
final unit="K",
displayUnit="degC")
"Leaving water temperature";
Buildings.DHC.Plants.Cooling.Subsystems.CoolingTowersParallel cooTowSys(
redeclare final package Medium=Medium,
final use_inputFilter=false,
final num=num,
final show_T=show_T,
final m_flow_small=m_flow_nominal,
final allowFlowReversal=allowFlowReversal,
final m_flow_nominal=m_flow_nominal/num,
final dpValve_nominal=dpValve_nominal,
final dp_nominal=dp_nominal,
final ratWatAir_nominal=ratWatAir_nominal,
final TAirInWB_nominal=TAirInWB_nominal,
final TWatIn_nominal=TWatIn_nominal,
final dT_nominal=dT_nominal,
final PFan_nominal=PFan_nominal,
final energyDynamics=energyDynamics)
"Cooling tower system";
Buildings.Fluid.Actuators.Valves.TwoWayEqualPercentage valByp(
redeclare final package Medium=Medium,
final allowFlowReversal=allowFlowReversal,
final m_flow_nominal=m_flow_nominal,
final show_T=show_T,
final dpValve_nominal=dpValve_nominal,
final riseTime=riseTime,
final use_inputFilter=use_inputFilter)
"Condenser water bypass valve";
Buildings.Fluid.Sensors.TemperatureTwoPort senTCWSup(
redeclare final package Medium=Medium,
final allowFlowReversal=allowFlowReversal,
final m_flow_nominal=m_flow_nominal,
final m_flow_small=m_flow_nominal,
final T_start=Medium.T_default)
"Temperature sensor";
Buildings.Controls.OBC.CDL.Reals.Sources.Constant TSetByp(
final k=TMin)
"Bypass loop temperature setpoint";
Buildings.Controls.OBC.CDL.Reals.PIDWithReset bypValCon(
u_s(
final unit="K",
displayUnit="degC"),
u_m(
final unit="K",
displayUnit="degC"),
controllerType=Modelica.Blocks.Types.SimpleController.PI,
final k=k,
final Ti=Ti,
final y_reset=0)
"Bypass valve controller";
Buildings.Controls.OBC.CDL.Reals.PID cooTowSpeCon(
u_s(
final unit="K",
displayUnit="degC"),
u_m(
final unit="K",
displayUnit="degC"),
final reverseActing=false,
final controllerType=controllerType,
final k=k,
final Ti=Ti)
"Cooling tower fan speed controller";
Buildings.Controls.OBC.CDL.Reals.Switch swi
"Output the input of higher value";
Buildings.Controls.OBC.CDL.Reals.Hysteresis hys(
uLow=TMin-0.1,
uHigh=TMin+0.1)
"Compare if (TWetBul+dTApp) is greater than TMin";
Buildings.Controls.OBC.CDL.Reals.AddParameter addPar(
p=dTApp)
"Add approach temperature on top of wetbulb temperature";
Buildings.Fluid.FixedResistances.Junction jun(
redeclare final package Medium=Medium,
m_flow_nominal=m_flow_nominal .* {1,-1,-1},
dp_nominal={0,0,0},
energyDynamics=Modelica.Fluid.Types.Dynamics.SteadyState)
"Upstream mixing point of cooTowSys and valByp";
protected
parameter Boolean enableTi=
controllerType == Modelica.Blocks.Types.SimpleController.PI or
controllerType == Modelica.Blocks.Types.SimpleController.PID
"Flag to enable controller parameter Ti";
parameter Boolean enableTd=
controllerType == Modelica.Blocks.Types.SimpleController.PD or
controllerType == Modelica.Blocks.Types.SimpleController.PID
"Flag to enable controller parameter Td";
equation
connect(cooTowSys.TWetBul,TWetBul);
connect(cooTowSys.port_b,senTCWSup.port_a);
connect(senTCWSup.port_b,port_b);
connect(TSetByp.y,bypValCon.u_s);
connect(senTCWSup.T,bypValCon.u_m);
connect(valByp.port_b,senTCWSup.port_a);
connect(cooTowSpeCon.y,cooTowSys.uFanSpe);
connect(cooTowSys.PFan,PFan);
connect(bypValCon.y,valByp.y);
connect(senTCWSup.T,cooTowSpeCon.u_m);
connect(hys.y, swi.u2);
connect(cooTowSpeCon.u_s,swi.y);
connect(TSetByp.y,swi.u3);
connect(TWetBul,addPar.u);
connect(addPar.y,swi.u1);
connect(on,cooTowSys.on);
connect(on[1],bypValCon.trigger);
connect(port_a, jun.port_1);
connect(cooTowSys.port_a, jun.port_2);
connect(valByp.port_a, jun.port_3);
connect(addPar.y, hys.u);
connect(senTCWSup.T, TLvg);
end CoolingTowersWithBypass;