This package contains components models for cooling towers.
The model Buildings.Fluid.HeatExchangers.CoolingTowers.FixedApproach computes a fixed approach temperature.
The model Buildings.Fluid.HeatExchangers.CoolingTowers.YorkCalc computes the cooling tower performance based the York formula.
Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).
| Name | Description |
|---|---|
 FixedApproach
| Cooling tower with constant approach temperature |
 YorkCalc
| Cooling tower with variable speed using the York calculation for the approach temperature |
 Examples
| Collection of models that illustrate model use and test models |
 Correlations
| Package with correlations for cooling tower performance |
 BaseClasses
| Package with base classes for Buildings.Fluid.HeatExchangers.CoolingTowers |
Buildings.Fluid.HeatExchangers.CoolingTowers.FixedApproach
Model for a steady-state or dynamic cooling tower with constant approach temperature.
The approach temperature is the difference between the leaving water temperature and
the entering air temperature.
The entering air temperature is used from the signal TAir. If
connected to the a dry-bulb temperature, then a dry cooling tower is modeled.
If connected to a wet-bulb temperature, then a wet cooling tower is modeled.
By connecting a signal that contains either the dry-bulb or the wet-bulb temperature, this model can be used to estimate the water return temperature from a cooling tower. For a more detailed model, use for example the YorkCalc model.
Extends from Buildings.Fluid.HeatExchangers.CoolingTowers.BaseClasses.CoolingTower (Base class for cooling towers).
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | PartialMedium | Medium in the component | |
| TemperatureDifference | TApp | 2 | Approach temperature difference [K] |
| Nominal condition | |||
| MassFlowRate | m_flow_nominal | Nominal mass flow rate [kg/s] | |
| Pressure | dp_nominal | Pressure [Pa] | |
| Initialization | |||
| MassFlowRate | m_flow.start | 0 | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s] |
| Pressure | dp.start | 0 | Pressure difference between port_a and port_b [Pa] |
| Assumptions | |||
| Boolean | allowFlowReversal | system.allowFlowReversal | = true to allow flow reversal, false restricts to design direction (port_a -> port_b) |
| Advanced | |||
| MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s] |
| Boolean | homotopyInitialization | true | = true, use homotopy method |
| Diagnostics | |||
| Boolean | show_V_flow | false | = true, if volume flow rate at inflowing port is computed |
| Boolean | show_T | true | = true, if actual temperature at port is computed (may lead to events) |
| Flow resistance | |||
| Boolean | from_dp | false | = true, use m_flow = f(dp) else dp = f(m_flow) |
| Boolean | linearizeFlowResistance | false | = true, use linear relation between m_flow and dp for any flow rate |
| Real | deltaM | 0.1 | Fraction of nominal flow rate where flow transitions to laminar |
| Dynamics | |||
| Nominal condition | |||
| Time | tau | 30 | Time constant at nominal flow (if energyDynamics <> SteadyState) [s] |
| Equations | |||
| Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance |
| Dynamics | massDynamics | energyDynamics | Formulation of mass balance |
| Initialization | |||
| AbsolutePressure | p_start | Medium.p_default | Start value of pressure [Pa] |
| Temperature | T_start | Medium.T_default | Start value of temperature [K] |
| MassFraction | X_start[Medium.nX] | Medium.X_default | Start value of mass fractions m_i/m [kg/kg] |
| ExtraProperty | C_start[Medium.nC] | fill(0, Medium.nC) | Start value of trace substances |
| Type | Name | Description |
|---|---|---|
| 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) |
| output RealOutput | TLvg | Leaving water temperature |
| input RealInput | TAir | Entering air dry or wet bulb temperature [K] |
model FixedApproach
"Cooling tower with constant approach temperature"
extends Buildings.Fluid.HeatExchangers.CoolingTowers.BaseClasses.CoolingTower;
parameter Modelica.SIunits.TemperatureDifference TApp(min=0, displayUnit="K") = 2
"Approach temperature difference";
Modelica.Blocks.Interfaces.RealInput TAir(min=0, unit="K")
"Entering air dry or wet bulb temperature";
equation
TAppAct=TApp;
TAirHT=TAir;
end FixedApproach;
Buildings.Fluid.HeatExchangers.CoolingTowers.YorkCalc
Model for a steady-state or dynamic cooling tower with variable speed fan using the York calculation for the approach temperature at off-design conditions.
To compute the thermal performance, this model takes as parameters the approach temperature, the range temperature and the inlet air wet bulb temperature at the design condition. Since the design mass flow rate (of the chiller condenser loop) is also a parameter, these parameters define the rejected heat.
For off-design conditions, the model uses the actual range temperature and a polynomial
to compute the approach temperature for free convection and for forced convection, i.e.,
with the fan operating. The polynomial is valid for a York cooling tower.
If the fan input signal y is below the minimum fan revolution yMin,
then the cooling tower operates in free convection mode, otherwise it operates in
the forced convection mode.
For numerical reasons, this transition occurs in the range of y ∈ [0.9*yMin, yMin].
The fan power consumption at the design condition can be specified as follows:
fraPFan_nominal can be used to specify at the
nominal conditions the fan power divided by the water flow rate. The default value is
275 Watts for a water flow rate of 0.15 kg/s.
PFan_nominal can be set to the fan power at nominal conditions.
If a user does not set this parameter, then the fan power will be
PFan_nominal = fraPFan_nominal * m_flow_nominal, where m_flow_nominal
is the nominal water flow rate.
In the forced convection mode, the actual fan power is
computed as PFan=fanRelPow(y) * PFan_nominal, where
the default value for the fan relative power consumption at part load is
fanRelPow(y)=y3.
In the free convection mode, the fan power consumption is zero.
For numerical reasons, the transition of fan power from the part load mode
to zero power consumption in the free convection mode occurs in the range
y ∈ [0.9*yMin, yMin].
To change the fan relative power consumption at part load in the forced convection mode,
points of fan controls signal and associated relative power consumption can be specified.
In between these points, the values are interpolated using cubic splines.
This model is similar to the model
y.
EnergyPlus 2.0.0 Engineering Reference, April 9, 2007.
Extends from Buildings.Fluid.HeatExchangers.CoolingTowers.BaseClasses.CoolingTower (Base class for cooling towers).
| Type | Name | Default | Description |
|---|---|---|---|
| replaceable package Medium | PartialMedium | Medium in the component | |
| Real | fraPFan_nominal | 275/0.15 | Fan power divived by water mass flow rate at design condition [W/(kg/s)] |
| Power | PFan_nominal | fraPFan_nominal*m_flow_nominal | Fan power [W] |
| efficiencyParameters | fanRelPow | Fan relative power consumption as a function of control signal, fanRelPow=P(y)/P(y=1) | |
| Real | yMin | 0.3 | Minimum control signal until fan is switched off (used for smoothing between forced and free convection regime) |
| Real | fraFreCon | 0.125 | Fraction of tower capacity in free convection regime |
| Nominal condition | |||
| MassFlowRate | m_flow_nominal | Nominal mass flow rate [kg/s] | |
| Pressure | dp_nominal | Pressure [Pa] | |
| Temperature | TAirInWB_nominal | 273.15 + 25.55 | Design inlet air wet bulb temperature [K] |
| TemperatureDifference | TApp_nominal | 3.89 | Design approach temperature [K] |
| TemperatureDifference | TRan_nominal | 5.56 | Design range temperature (water in - water out) [K] |
| Initialization | |||
| MassFlowRate | m_flow.start | 0 | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s] |
| Pressure | dp.start | 0 | Pressure difference between port_a and port_b [Pa] |
| Assumptions | |||
| Boolean | allowFlowReversal | system.allowFlowReversal | = true to allow flow reversal, false restricts to design direction (port_a -> port_b) |
| Advanced | |||
| MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s] |
| Boolean | homotopyInitialization | true | = true, use homotopy method |
| Diagnostics | |||
| Boolean | show_V_flow | false | = true, if volume flow rate at inflowing port is computed |
| Boolean | show_T | true | = true, if actual temperature at port is computed (may lead to events) |
| Flow resistance | |||
| Boolean | from_dp | false | = true, use m_flow = f(dp) else dp = f(m_flow) |
| Boolean | linearizeFlowResistance | false | = true, use linear relation between m_flow and dp for any flow rate |
| Real | deltaM | 0.1 | Fraction of nominal flow rate where flow transitions to laminar |
| Dynamics | |||
| Nominal condition | |||
| Time | tau | 30 | Time constant at nominal flow (if energyDynamics <> SteadyState) [s] |
| Equations | |||
| Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance |
| Dynamics | massDynamics | energyDynamics | Formulation of mass balance |
| Initialization | |||
| AbsolutePressure | p_start | Medium.p_default | Start value of pressure [Pa] |
| Temperature | T_start | Medium.T_default | Start value of temperature [K] |
| MassFraction | X_start[Medium.nX] | Medium.X_default | Start value of mass fractions m_i/m [kg/kg] |
| ExtraProperty | C_start[Medium.nC] | fill(0, Medium.nC) | Start value of trace substances |
| Type | Name | Description |
|---|---|---|
| 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) |
| output RealOutput | TLvg | Leaving water temperature |
| input RealInput | TAir | Entering air wet bulb temperature [K] |
| input RealInput | y | Fan control signal |
model YorkCalc
"Cooling tower with variable speed using the York calculation for the approach temperature"
extends Buildings.Fluid.HeatExchangers.CoolingTowers.BaseClasses.CoolingTower;
import cha = Buildings.Fluid.Movers.BaseClasses.Characteristics;
parameter Modelica.SIunits.Temperature TAirInWB_nominal = 273.15+25.55
"Design inlet air wet bulb temperature";
parameter Modelica.SIunits.TemperatureDifference TApp_nominal(displayUnit="K") = 3.89
"Design approach temperature";
parameter Modelica.SIunits.TemperatureDifference TRan_nominal(displayUnit="K") = 5.56
"Design range temperature (water in - water out)";
parameter Real fraPFan_nominal(unit="W/(kg/s)") = 275/0.15
"Fan power divived by water mass flow rate at design condition";
parameter Modelica.SIunits.Power PFan_nominal = fraPFan_nominal*m_flow_nominal
"Fan power";
parameter Buildings.Fluid.Movers.BaseClasses.Characteristics.efficiencyParameters
fanRelPow(
r_V = {0, 0.1, 0.3, 0.6, 1},
eta = {0, 0.1^3, 0.3^3, 0.6^3, 1})
"Fan relative power consumption as a function of control signal, fanRelPow=P(y)/P(y=1)";
parameter Real yMin(min=0.01, max=1) = 0.3
"Minimum control signal until fan is switched off (used for smoothing between forced and free convection regime)";
parameter Real fraFreCon(min=0, max=1) = 0.125
"Fraction of tower capacity in free convection regime";
Modelica.Blocks.Interfaces.RealInput TAir(min=0, unit="K")
"Entering air wet bulb temperature";
Buildings.Fluid.HeatExchangers.CoolingTowers.Correlations.BoundsYorkCalc bou
"Bounds for correlation";
Modelica.Blocks.Interfaces.RealInput y "Fan control signal";
Modelica.SIunits.TemperatureDifference TRan(nominal=1, displayUnit="K")
"Range temperature";
Modelica.SIunits.MassFraction FRWat
"Ratio actual over design water mass flow ratio";
Modelica.SIunits.MassFraction FRAir
"Ratio actual over design air mass flow ratio";
Modelica.SIunits.Power PFan "Fan power";
protected
parameter Modelica.SIunits.MassFraction FRWat0(min=0, start=1, fixed=false)
"Ratio actual over design water mass flow ratio at nominal condition";
parameter Modelica.SIunits.Temperature TWatIn0(fixed=false)
"Water inlet temperature at nominal condition";
parameter Modelica.SIunits.Temperature TWatOut_nominal(fixed=false)
"Water outlet temperature at nominal condition";
parameter Modelica.SIunits.MassFlowRate mRef_flow(min=0, start=m_flow_nominal, fixed=false)
"Reference water flow rate";
Modelica.SIunits.TemperatureDifference dTMax(nominal=1, displayUnit="K")
"Maximum possible temperature difference";
Modelica.SIunits.TemperatureDifference TAppCor(min=0, nominal=1, displayUnit="K")
"Approach temperature for forced convection";
Modelica.SIunits.TemperatureDifference TAppFreCon(min=0, nominal=1, displayUnit="K")
"Approach temperature for free convection";
final parameter Real fanRelPowDer[size(fanRelPow.r_V,1)](fixed=false)
"Coefficients for fan relative power consumption as a function of control signal";
initial equation
TWatOut_nominal = TAirInWB_nominal + TApp_nominal;
TRan_nominal = TWatIn0 - TWatOut_nominal; // by definition of the range temp.
TApp_nominal = Buildings.Fluid.HeatExchangers.CoolingTowers.Correlations.yorkCalc(
TRan=TRan_nominal, TWetBul=TAirInWB_nominal,
FRWat=FRWat0, FRAir=1); // this will be solved for FRWat0
mRef_flow = m_flow_nominal/FRWat0;
// Derivatives for spline that interpolates the fan relative power
fanRelPowDer = Buildings.Utilities.Math.Functions.splineDerivatives(
x=fanRelPow.r_V,
y=fanRelPow.eta);
// Check validity of relative fan power consumption at y=yMin and y=1
assert(cha.efficiency(data=fanRelPow, r_V=yMin, d=fanRelPowDer) > -1E-4,
"The fan relative power consumption must be non-negative for y=0."
+ "\n Obtained fanRelPow(0) = " + String(cha.efficiency(data=fanRelPow, r_V=yMin, d=fanRelPowDer))
+ "\n You need to choose different values for the parameter fanRelPow.");
assert(abs(1-cha.efficiency(data=fanRelPow, r_V=1, d=fanRelPowDer))<1E-4, "The fan relative power consumption must be one for y=1."
+ "\n Obtained fanRelPow(1) = " + String(cha.efficiency(data=fanRelPow, r_V=1, d=fanRelPowDer))
+ "\n You need to choose different values for the parameter fanRelPow."
+ "\n To increase the fan power, change fraPFan_nominal or PFan_nominal.");
equation
// Air temperature used for the heat transfer
TAirHT=TAir;
// Range temperature
TRan = Medium.temperature(sta_a) - Medium.temperature(sta_b);
// Fractional mass flow rates
FRWat = m_flow/mRef_flow;
FRAir = y;
TAppCor = Buildings.Fluid.HeatExchangers.CoolingTowers.Correlations.yorkCalc(
TRan=TRan, TWetBul=TAir,
FRWat=FRWat, FRAir=max(FRWat/bou.liqGasRat_max, FRAir));
dTMax = Medium.temperature(sta_a) - TAir;
TAppFreCon = (1-fraFreCon) * dTMax + fraFreCon *
Buildings.Fluid.HeatExchangers.CoolingTowers.Correlations.yorkCalc(
TRan=TRan, TWetBul=TAir, FRWat=FRWat, FRAir=1);
// Actual approach temperature and fan power consumption,
// which depends on forced vs. free convection.
// The transition is for y in [yMin-yMin/10, yMin]
[TAppAct, PFan] = Buildings.Utilities.Math.Functions.spliceFunction(
pos=[TAppCor,
cha.efficiency(
data=fanRelPow, r_V=y, d=fanRelPowDer) * PFan_nominal],
neg=[TAppFreCon, 0],
x=y-yMin+yMin/20,
deltax=yMin/20);
end YorkCalc;