Buildings.Utilities.Psychrometrics

Information

This package contains blocks and functions for psychrometric calculations.

Package Content

Name	Description
X_pW	Humidity ratio for given water vapor pressure
pW_X	Water vapor pressure for given humidity ratio
X_pTphi	Return steam mass fraction as a function of relative humidity phi and temperature T
TDewPoi_pW	Model to compute the dew point temperature for given water vapor pressure of moist air
ToDryAir	Block to convert absolute humidity from [kg/kg total air] to [kg/kg dry air]
ToTotalAir	Block to convert absolute humidity from [kg/kg dry air] to [kg/kg total air]
TWetBul_TDryBulPhi	Model to compute the wet bulb temperature based on relative humidity
TWetBul_TDryBulXi	Model to compute the wet bulb temperature based on mass fraction
pW_TDewPoi	Model to compute the water vapor pressure for a given dew point temperature of moist air
WetBul_pTX	Block to compute the wet bulb condition for given dry bulb temperature and humidity
Functions	Package with psychrometric functions
Examples	Collection of models that illustrate model use and test models
BaseClasses	Package with base classes for Buildings.Utilities.Psychrometrics

Buildings.Utilities.Psychrometrics.X_pW

Information

Block to compute the humidity ratio for a given water vapor partial pressure.

If use_p_in is false (default option), the p parameter is used as atmospheric pressure, and the p_in input connector is disabled; if use_p_in is true, then the p parameter is ignored, and the value provided by the input connector is used instead.

Parameters

Type	Name	Default	Description
Boolean	use_p_in	true	Get the pressure from the input connector
Pressure	p	101325	Fixed value of pressure [Pa]

Connectors

Type	Name	Description
input RealInput	p_in	Atmospheric Pressure [Pa]
output RealOutput	X_w	Species concentration at dry bulb temperature
input RealInput	p_w	Water vapor pressure [Pa]

Modelica definition

block X_pW "Humidity ratio for given water vapor pressure"
  extends Buildings.Utilities.Psychrometrics.BaseClasses.HumidityRatioVaporPressure;
  Modelica.Blocks.Interfaces.RealOutput X_w(min=0, max=1, nominal=0.01) 
    "Species concentration at dry bulb temperature";
  Modelica.Blocks.Interfaces.RealInput p_w(final quantity="Pressure",
                                           final unit="Pa",
                                           displayUnit="Pa",
                                           min = 0.003,
                                           start=2000,
                                           nominal=1000) "Water vapor pressure";
  output Modelica.SIunits.MassFraction x_w(min=0, max=1, nominal=0.01, start=0.001) 
    "Water mass fraction per mass of dry air";
equation 
  X_w = Buildings.Utilities.Psychrometrics.Functions.X_pW(p_w=p_w, p=p_in_internal);
  x_w = X_w/(1-X_w);
end X_pW;

Buildings.Utilities.Psychrometrics.pW_X

Information

Block to compute the water vapor partial pressure for a given humidity ratio.

If use_p_in is false (default option), the p parameter is used as atmospheric pressure, and the p_in input connector is disabled; if use_p_in is true, then the p parameter is ignored, and the value provided by the input connector is used instead.

Parameters

Type	Name	Default	Description
Boolean	use_p_in	true	Get the pressure from the input connector
Pressure	p	101325	Fixed value of pressure [Pa]

Connectors

Type	Name	Description
input RealInput	p_in	Atmospheric Pressure [Pa]
input RealInput	X_w	Species concentration at dry bulb temperature
output RealOutput	p_w	Water vapor pressure [Pa]

Modelica definition

block pW_X "Water vapor pressure for given humidity ratio"
  extends Buildings.Utilities.Psychrometrics.BaseClasses.HumidityRatioVaporPressure;
  Modelica.Blocks.Interfaces.RealInput X_w(min=0, max=1, nominal=0.01) 
    "Species concentration at dry bulb temperature";
  Modelica.Blocks.Interfaces.RealOutput p_w(final quantity="Pressure",
                                           final unit="Pa",
                                           displayUnit="Pa",
                                           min = 0) "Water vapor pressure";

  output Modelica.SIunits.MassFraction x_w(min=0, max=1, nominal=0.01, start=0.001) 
    "Water mass fraction per mass of dry air";

equation 
  p_w = Buildings.Utilities.Psychrometrics.Functions.pW_X(X_w=X_w, p=p_in_internal);
  x_w = X_w/(1-X_w);
end pW_X;

Buildings.Utilities.Psychrometrics.X_pTphi

Information

Block to compute the water vapor concentration based on pressure, temperature and relative humidity.

If use_p_in is false (default option), the p parameter is used as atmospheric pressure, and the p_in input connector is disabled; if use_p_in is true, then the p parameter is ignored, and the value provided by the input connector is used instead.

Parameters

Type	Name	Default	Description
Boolean	use_p_in	true	Get the pressure from the input connector
Pressure	p	101325	Fixed value of pressure [Pa]

Connectors

Type	Name	Description
input RealInput	p_in	Atmospheric Pressure [Pa]
input RealInput	T	Temperature [K]
input RealInput	phi	Relative humidity (0...1)
output RealOutput	X[Medium.nX]	Steam mass fraction

Modelica definition

block X_pTphi 
  "Return steam mass fraction as a function of relative humidity phi and temperature T"
  extends Buildings.Utilities.Psychrometrics.BaseClasses.HumidityRatioVaporPressure;
  package Medium = Buildings.Media.PerfectGases.MoistAirUnsaturated 
    "Medium model";

public 
  Modelica.Blocks.Interfaces.RealInput T(final unit="K",
                                           displayUnit="degC",
                                           min = 0) "Temperature";
  Modelica.Blocks.Interfaces.RealInput phi(min = 0, max=1) 
    "Relative humidity (0...1)";
  Modelica.Blocks.Interfaces.RealOutput X[Medium.nX](each min=0, each max=1) 
    "Steam mass fraction";
protected 
  constant Real k = 0.621964713077499 "Ratio of molar masses";
  Modelica.SIunits.AbsolutePressure psat "Saturation pressure";
 parameter Integer i_w(min=1, fixed=false) "Index for water substance";
 parameter Integer i_nw(min=1, fixed=false) "Index for non-water substance";
 parameter Boolean found(fixed=false) "Flag, used for error checking";
initial algorithm 
  found:=false;
  i_w :=1;
    for i in 1:Medium.nXi loop
      if Modelica.Utilities.Strings.isEqual(string1=Medium.substanceNames[i],
                                            string2="water",
                                            caseSensitive=false) then
        i_w :=i;
        found:=true;
      end if;
    end for;
  i_nw := if i_w == 1 then 2 else 1;
  assert(found, "Did not find medium species 'water' in the medium model. Change medium model.");
algorithm 
  psat := Buildings.Media.PerfectGases.MoistAirUnsaturated.saturationPressure(T);
  X[i_w] := Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
     pSat=psat, p=p_in_internal, phi=phi);
  //sum(X[:]) = 1; // The formulation with a sum in an equation section leads to a nonlinear equation system
  X[i_nw] := 1 - X[i_w];
end X_pTphi;

Buildings.Utilities.Psychrometrics.TDewPoi_pW

Information

Dew point temperature calculation for moist air above freezing temperature.

The correlation used in this model is valid for dew point temperatures between 0 degC and 200 degC. It is the correlation from 2005 ASHRAE Handbook, p. 6.2. In an earlier version of this model, the equation from Peppers has been used, but this equation yielded about 15 Kelvin lower dew point temperatures.

Connectors

Type	Name	Description
input RealInput	p_w	Water vapor partial pressure
output RealOutput	T	Dew point temperature [K]

Modelica definition

block TDewPoi_pW 
  "Model to compute the dew point temperature for given water vapor pressure of moist air"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  Modelica.Blocks.Interfaces.RealInput p_w "Water vapor partial pressure";
  Modelica.Blocks.Interfaces.RealOutput T(start=278.15,
                                         final quantity="ThermodynamicTemperature",
                                         final unit="K",
                                         min = 0,
                                         displayUnit="degC") 
    "Dew point temperature";

equation 
 p_w = Buildings.Utilities.Psychrometrics.Functions.pW_TDewPoi(T=T);
end TDewPoi_pW;

Buildings.Utilities.Psychrometrics.ToDryAir

Information

Block that converts humidity concentration from [kg/kg total air] to [kg/kg dry air].

Connectors

Type	Name	Description
output RealOutput	XiDry	Water vapor concentration in [kg/kg dry air]
input RealInput	XiTotalAir	Water vapor concentration in [kg/kg total air]

Modelica definition

block ToDryAir 
  "Block to convert absolute humidity from [kg/kg total air] to [kg/kg dry air]"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  Modelica.Blocks.Interfaces.RealOutput XiDry 
    "Water vapor concentration in [kg/kg dry air]";
  Modelica.Blocks.Interfaces.RealInput XiTotalAir 
    "Water vapor concentration in [kg/kg total air]";

equation 
  XiDry = XiTotalAir / (1-XiTotalAir);
end ToDryAir;

Buildings.Utilities.Psychrometrics.ToTotalAir

Information

Block that converts humidity concentration from [kg/kg dry air] to [kg/kg total air].

This block may be used, for example, to convert absolute humidity that is received from EnergyPlus to [kg/kg total air], which is the convention used by Modelica.Media.

Connectors

Type	Name	Description
output RealOutput	XiTotalAir	Water vapor concentration in [kg/kg total air]
input RealInput	XiDry	Water vapor concentration in [kg/kg dry air]
output RealOutput	XNonVapor	Mass fraction of remaining substances

Modelica definition

block ToTotalAir 
  "Block to convert absolute humidity from [kg/kg dry air] to [kg/kg total air]"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  Modelica.Blocks.Interfaces.RealOutput XiTotalAir 
    "Water vapor concentration in [kg/kg total air]";
  Modelica.Blocks.Interfaces.RealInput XiDry 
    "Water vapor concentration in [kg/kg dry air]";

  Modelica.Blocks.Interfaces.RealOutput XNonVapor 
    "Mass fraction of remaining substances";
equation 
  XiTotalAir = XiDry / (1+XiDry);
  XNonVapor = 1 - XiTotalAir;
end ToTotalAir;

Buildings.Utilities.Psychrometrics.TWetBul_TDryBulPhi

Information

This block computes the the wet bulb temperature for a given dry bulb temperature, relative air humidity and atmospheric pressure.

If the constant approximateWetBulb is true, then the block uses the approximation of Stull (2011) to compute the wet bulb temperature without requiring a nonlinear equation. Otherwise, the model will introduce one nonlinear equation.

The approximation by Stull is valid for a relative humidity of 5% to 99%, a temperature range from -20ˆC to 50ˆC and standard sea level pressure. For this range of data, the approximation error is -1 Kelvin to +0.65 Kelvin, with a mean error of less than 0.3 Kelvin.

For a model that takes the mass fraction instead of the relative humidity as an input, see Buildings.Utilities.Psychrometrics.TWetBul_TDryBulXi.

References

Stull, Roland. Wet-Bulb Temperature from Relative Humidity and Air Temperature Roland Stull. Journal of Applied Meteorology and Climatology. Volume 50, Issue 11, pp. 2267-2269. November 2011 DOI: 10.1175/JAMC-D-11-0143.1

Parameters

Type	Name	Default	Description
replaceable package Medium		Modelica.Media.Interfaces.Pa...	Medium model
Boolean	approximateWetBulb	false	Set to true to approximate wet bulb temperature

Connectors

Type	Name	Description
replaceable package Medium		Medium model
input RealInput	TDryBul	Dry bulb temperature [K]
input RealInput	phi	Relative air humidity
input RealInput	p	Pressure [Pa]
output RealOutput	TWetBul	Wet bulb temperature [K]

Modelica definition

block TWetBul_TDryBulPhi 
  "Model to compute the wet bulb temperature based on relative humidity"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  replaceable package Medium =
    Modelica.Media.Interfaces.PartialCondensingGases "Medium model";

  parameter Boolean approximateWetBulb=false 
    "Set to true to approximate wet bulb temperature";
  Modelica.Blocks.Interfaces.RealInput TDryBul(
    start=303,
    final quantity="ThermodynamicTemperature",
    final unit="K",
    min=0) "Dry bulb temperature";

  Modelica.Blocks.Interfaces.RealInput phi(min=0, max=1) 
    "Relative air humidity";

  Modelica.Blocks.Interfaces.RealInput p(  final quantity="Pressure",
                                           final unit="Pa",
                                           min = 0) "Pressure";

  Modelica.Blocks.Interfaces.RealOutput TWetBul(
    start=293,
    final quantity="ThermodynamicTemperature",
    final unit="K",
    min=0) "Wet bulb temperature";

protected 
  constant Modelica.Media.IdealGases.Common.DataRecord dryair = Modelica.Media.IdealGases.Common.SingleGasesData.Air;
  constant Modelica.Media.IdealGases.Common.DataRecord steam = Modelica.Media.IdealGases.Common.SingleGasesData.H2O;
  constant Real k_mair =  steam.MM/dryair.MM "ratio of molar weights";
  Modelica.SIunits.Conversions.NonSIunits.Temperature_degC TDryBul_degC 
    "Dry bulb temperature in degree Celsius";
  Real rh_per(min=0) "Relative humidity in percentage";
  Modelica.SIunits.MassFraction XiDryBul 
    "Water vapor mass fraction at dry bulb state";
  Modelica.SIunits.MassFraction XiSat "Water vapor mass fraction at saturation";
  constant Modelica.SIunits.SpecificHeatCapacity cpAir=
     Buildings.Media.PerfectGases.Common.SingleGasData.Air.cp 
    "Specific heat capacity of air";
  constant Modelica.SIunits.SpecificHeatCapacity cpSte=
     Buildings.Media.PerfectGases.Common.SingleGasData.H2O.cp 
    "Specific heat capacity of water vapor";
  constant Modelica.SIunits.SpecificEnthalpy h_fg = 2501014.5 
    "Specific heat capacity of water vapor";
equation 
  if approximateWetBulb then
    TDryBul_degC = TDryBul - 273.15;
    rh_per       = 100*phi;
    TWetBul      = 273.15 + TDryBul_degC
       * Modelica.Math.atan(0.151977 * sqrt(rh_per + 8.313659))
       + Modelica.Math.atan(TDryBul_degC + rh_per)
       - Modelica.Math.atan(rh_per-1.676331)
       + 0.00391838 * rh_per^(1.5) * Modelica.Math.atan( 0.023101 * rh_per)  - 4.686035;
    XiSat    = 0;
    XiDryBul = 0;
  else
    XiSat   = Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
      pSat=   Medium.saturationPressureLiquid(Tsat=TWetBul),
      p=     p,
      phi=   1);
    XiDryBul =Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
      p=p,
      pSat=Medium.saturationPressureLiquid(Tsat=TDryBul),
      phi=phi);
    TWetBul = (TDryBul * ((1-XiDryBul) * cpAir + XiDryBul * cpSte) + (XiDryBul-XiSat) * h_fg)/
            ( (1-XiSat)*cpAir + XiSat * cpSte);
    TDryBul_degC = 0;
    rh_per       = 0;
  end if;

end TWetBul_TDryBulPhi;

Buildings.Utilities.Psychrometrics.TWetBul_TDryBulXi

Information

This block computes the the wet bulb temperature for a given dry bulb temperature, mass fraction and atmospheric pressure.

If the constant approximateWetBulb is true, then the block uses the approximation of Stull (2011) to compute the wet bulb temperature without requiring a nonlinear equation. Otherwise, the model will introduce one nonlinear equation.

The approximation by Stull is valid for a relative humidity of 5% to 99%, a temperature range from -20ˆC to 50ˆC and standard sea level pressure. For this range of data, the approximation error is -1 Kelvin to +0.65 Kelvin, with a mean error of less than 0.3 Kelvin.

For a model that takes the relative humidity instead of the mass fraction as an input, see Buildings.Utilities.Psychrometrics.TWetBul_TDryBulPhi.

For a use of this model, see for example Buildings.Fluid.Sensors.WetBulbTemperature

References

Stull, Roland. Wet-Bulb Temperature from Relative Humidity and Air Temperature Roland Stull. Journal of Applied Meteorology and Climatology. Volume 50, Issue 11, pp. 2267-2269. November 2011 DOI: 10.1175/JAMC-D-11-0143.1

Parameters

Type	Name	Default	Description
replaceable package Medium		Modelica.Media.Interfaces.Pa...	Medium model
Boolean	approximateWetBulb	false	Set to true to approximate wet bulb temperature

Connectors

Type	Name	Description
replaceable package Medium		Medium model
input RealInput	TDryBul	Dry bulb temperature [K]
input RealInput	p	Pressure [Pa]
output RealOutput	TWetBul	Wet bulb temperature [K]
input RealInput	Xi[Medium.nXi]	Species concentration at dry bulb temperature

Modelica definition

block TWetBul_TDryBulXi 
  "Model to compute the wet bulb temperature based on mass fraction"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  replaceable package Medium =
    Modelica.Media.Interfaces.PartialCondensingGases "Medium model";

  parameter Boolean approximateWetBulb=false 
    "Set to true to approximate wet bulb temperature";

  Modelica.Blocks.Interfaces.RealInput TDryBul(
    start=303,
    final quantity="ThermodynamicTemperature",
    final unit="K",
    min=0) "Dry bulb temperature";
  Modelica.Blocks.Interfaces.RealInput p(  final quantity="Pressure",
                                           final unit="Pa",
                                           min = 0) "Pressure";
  Modelica.Blocks.Interfaces.RealOutput TWetBul(
    start=293,
    final quantity="ThermodynamicTemperature",
    final unit="K",
    min=0) "Wet bulb temperature";
  Modelica.Blocks.Interfaces.RealInput Xi[Medium.nXi] 
    "Species concentration at dry bulb temperature";

protected 
  constant Modelica.Media.IdealGases.Common.DataRecord dryair = Modelica.Media.IdealGases.Common.SingleGasesData.Air;
  constant Modelica.Media.IdealGases.Common.DataRecord steam = Modelica.Media.IdealGases.Common.SingleGasesData.H2O;
  constant Real k_mair =  steam.MM/dryair.MM "ratio of molar weights";
  Modelica.SIunits.Conversions.NonSIunits.Temperature_degC TDryBul_degC 
    "Dry bulb temperature in degree Celsius";
  Real rh_per(min=0) "Relative humidity in percentage";

  Modelica.SIunits.MassFraction XiSat(start=0.01,
                                      nominal=0.01) 
    "Water vapor mass fraction at saturation";

 parameter Integer iWat(fixed=false) 
    "Index of water in medium composition vector";
  constant Modelica.SIunits.SpecificHeatCapacity cpAir=
     Buildings.Media.PerfectGases.Common.SingleGasData.Air.cp 
    "Specific heat capacity of air";
  constant Modelica.SIunits.SpecificHeatCapacity cpSte=
     Buildings.Media.PerfectGases.Common.SingleGasData.H2O.cp 
    "Specific heat capacity of water vapor";
  constant Modelica.SIunits.SpecificEnthalpy h_fg = 2501014.5 
    "Specific heat capacity of water vapor";
initial algorithm 
  iWat:=-1;
    for i in 1:Medium.nX loop
      if Modelica.Utilities.Strings.isEqual(string1=Medium.substanceNames[i],
                                            string2="Water", caseSensitive=false) then
        iWat :=i;
      end if;
    end for;
  assert(iWat > 0, "Did not find medium species 'water' in the medium model. Change medium model.");

equation 
  if approximateWetBulb then
    TDryBul_degC = TDryBul - 273.15;
    rh_per       = 100 * p/min(Medium.saturationPressure(TDryBul),0.999*p)*Xi[iWat]/(Xi[iWat] + k_mair*(1-Xi[iWat]));
    TWetBul      = 273.15 + TDryBul_degC
       * Modelica.Math.atan(0.151977 * sqrt(rh_per + 8.313659))
       + Modelica.Math.atan(TDryBul_degC + rh_per)
       - Modelica.Math.atan(rh_per-1.676331)
       + 0.00391838 * rh_per^(1.5) * Modelica.Math.atan( 0.023101 * rh_per)  - 4.686035;
    XiSat = 0;
  else
    XiSat   = Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
      pSat=   Medium.saturationPressureLiquid(Tsat=TWetBul),
      p=     p,
      phi=   1);
    TWetBul = (TDryBul * ((1-Xi[iWat]) * cpAir + Xi[iWat] * cpSte) + (Xi[iWat]-XiSat) * h_fg)/
            ( (1-XiSat)*cpAir + XiSat * cpSte);
    TDryBul_degC = 0;
    rh_per       = 0;
  end if;

end TWetBul_TDryBulXi;

Buildings.Utilities.Psychrometrics.pW_TDewPoi

Information

Block to compute the water vapor pressure for a given dew point temperature.

The correlation used in this model is valid for dew point temperatures between 0 degC and 200 degC. It is the correlation from 2005 ASHRAE Handbook, p. 6.2. In an earlier version of this model, the equation from Peppers has been used, but this equation yielded about 15 Kelvin lower dew point temperatures.

Connectors

Type	Name	Description
output RealOutput	p_w	Water vapor partial pressure
input RealInput	T	Dew point temperature [K]

Modelica definition

block pW_TDewPoi 
  "Model to compute the water vapor pressure for a given dew point temperature of moist air"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  Modelica.Blocks.Interfaces.RealOutput p_w "Water vapor partial pressure";
  Modelica.Blocks.Interfaces.RealInput T(final quantity="ThermodynamicTemperature",
                                         final unit="K",
                                         min = 0,
                                         displayUnit="degC") 
    "Dew point temperature";

equation 
 p_w = Buildings.Utilities.Psychrometrics.Functions.pW_TDewPoi_amb(T=T);
end pW_TDewPoi;

Buildings.Utilities.Psychrometrics.WetBul_pTX

Information

Block to compute the temperature and mass fraction at the wet bulb condition for a given dry bulb state.

Parameters

Type	Name	Default	Description
replaceable package Medium		Modelica.Media.Interfaces.Pa...	Medium model

Connectors

Type	Name	Description
replaceable package Medium		Medium model
input RealInput	TDryBul	Dry bulb temperature [K]
input RealInput	XDryBul	Dry bulb temperature [1]
input RealInput	p	Pressure [Pa]
output RealOutput	TWetBul	Wet bulb temperature [K]
output RealOutput	XWetBul	Water vapor mass fraction at wet bulb temperature [1]

Modelica definition

block WetBul_pTX 
  "Block to compute the wet bulb condition for given dry bulb temperature and humidity"
   extends Modelica.Blocks.Interfaces.BlockIcon;
  replaceable package Medium =
    Modelica.Media.Interfaces.PartialCondensingGases "Medium model";

  Modelica.Blocks.Interfaces.RealInput TDryBul(
    start=303,
    final quantity="ThermodynamicTemperature",
    final unit="K",
    min=0) "Dry bulb temperature";
  Modelica.Blocks.Interfaces.RealInput XDryBul(
    start=0.01,
    final quantity="ThermodynamicTemperature",
    final unit="1",
    min=0) "Dry bulb temperature";

  Modelica.Blocks.Interfaces.RealInput p(  final quantity="Pressure",
                                           final unit="Pa",
                                           min = 0) "Pressure";
  Modelica.Blocks.Interfaces.RealOutput TWetBul(
    start=293,
    final quantity="ThermodynamicTemperature",
    final unit="K",
    min=0) "Wet bulb temperature";

  Modelica.Blocks.Interfaces.RealOutput XWetBul(
    min=0,
    max=1,
    start=0.012,
    unit="1",
    nominal=0.01) "Water vapor mass fraction at wet bulb temperature";

protected 
  constant Modelica.SIunits.SpecificHeatCapacity cpAir=
     Buildings.Media.PerfectGases.Common.SingleGasData.Air.cp 
    "Specific heat capacity of air";
  constant Modelica.SIunits.SpecificHeatCapacity cpSte=
     Buildings.Media.PerfectGases.Common.SingleGasData.H2O.cp 
    "Specific heat capacity of water vapor";
  constant Modelica.SIunits.SpecificEnthalpy h_fg = 2501014.5 
    "Specific heat capacity of water vapor";
equation 
  XWetBul   = Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
      pSat=   Medium.saturationPressureLiquid(Tsat=TWetBul),
      p=     p,
      phi=   1);
  TWetBul = (TDryBul * ((1-XDryBul) * cpAir + XDryBul * cpSte) + (XDryBul-XWetBul) * h_fg)/
            ( (1-XWetBul)*cpAir + XWetBul * cpSte);
end WetBul_pTX;