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Buildings.Utilities.Psychrometrics

Library with psychrometric functions

Information

This package contains blocks and functions for psychrometric calculations.

The nomenclature used in this package is described at Buildings.UsersGuide.Conventions.

Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).

Package Content

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

Buildings.Utilities.Psychrometrics.SaturationPressure Buildings.Utilities.Psychrometrics.SaturationPressure

Saturation pressure as a function of temperature

Buildings.Utilities.Psychrometrics.SaturationPressure

Information

Saturation pressure of water, computed from temperature, according to Wagner et al. (1993). The range of validity is between 190 and 373.16 Kelvin.

References

Wagner W., A. Saul, A. Pruss. International equations for the pressure along the melting and along the sublimation curve of ordinary water substance, equation 3.5. 1993. http://www.nist.gov/data/PDFfiles/jpcrd477.pdf.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Connectors

TypeNameDescription
input RealInputTSatSaturation temperature [K]
output RealOutputpSatSaturation pressure [Pa]

Modelica definition

block SaturationPressure "Saturation pressure as a function of temperature" extends Modelica.Blocks.Icons.Block; Modelica.Blocks.Interfaces.RealInput TSat(unit="K", displayUnit="degC", nominal=300) "Saturation temperature"; Modelica.Blocks.Interfaces.RealOutput pSat(unit="Pa", displayUnit="Pa", nominal=1000) "Saturation pressure"; equation pSat = Buildings.Utilities.Psychrometrics.Functions.saturationPressure(TSat); end SaturationPressure;

Buildings.Utilities.Psychrometrics.SaturationPressureLiquid Buildings.Utilities.Psychrometrics.SaturationPressureLiquid

Saturation pressure as a function of temperature

Buildings.Utilities.Psychrometrics.SaturationPressureLiquid

Information

Saturation pressure of water above the triple point temperature computed from temperature. The range of validity is between 273.16 and 373.16 Kelvin.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Connectors

TypeNameDescription
input RealInputTSatSaturation temperature [K]
output RealOutputpSatSaturation pressure [Pa]

Modelica definition

block SaturationPressureLiquid "Saturation pressure as a function of temperature" extends Modelica.Blocks.Icons.Block; Modelica.Blocks.Interfaces.RealInput TSat(unit="K", displayUnit="degC", nominal=300) "Saturation temperature"; Modelica.Blocks.Interfaces.RealOutput pSat(unit="Pa", displayUnit="Pa", nominal=1000) "Saturation pressure"; equation pSat = Buildings.Utilities.Psychrometrics.Functions.saturationPressureLiquid(TSat); end SaturationPressureLiquid;

Buildings.Utilities.Psychrometrics.SublimationPressureIce Buildings.Utilities.Psychrometrics.SublimationPressureIce

Saturation pressure as a function of temperature

Buildings.Utilities.Psychrometrics.SublimationPressureIce

Information

Sublimation pressure of water below the triple point temperature, computed from temperature, according to Wagner et al. (1993). The range of validity is between 190 and 273.16 Kelvin.

References

Wagner W., A. Saul, A. Pruss. International equations for the pressure along the melting and along the sublimation curve of ordinary water substance, equation 3.5. 1993. http://www.nist.gov/data/PDFfiles/jpcrd477.pdf.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Connectors

TypeNameDescription
input RealInputTSatSaturation temperature [K]
output RealOutputpSatSaturation pressure [Pa]

Modelica definition

block SublimationPressureIce "Saturation pressure as a function of temperature" extends Modelica.Blocks.Icons.Block; Modelica.Blocks.Interfaces.RealInput TSat(unit="K", displayUnit="degC", nominal=300) "Saturation temperature"; Modelica.Blocks.Interfaces.RealOutput pSat(unit="Pa", displayUnit="Pa", nominal=1000) "Saturation pressure"; equation pSat = Buildings.Utilities.Psychrometrics.Functions.sublimationPressureIce(TSat); end SublimationPressureIce;

Buildings.Utilities.Psychrometrics.TDewPoi_pW Buildings.Utilities.Psychrometrics.TDewPoi_pW

Model to compute the dew point temperature for given water vapor pressure of moist air

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.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Connectors

TypeNameDescription
input RealInputp_wWater vapor partial pressure
output RealOutputTDew 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.Icons.Block; 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.TWetBul_TDryBulPhi Buildings.Utilities.Psychrometrics.TWetBul_TDryBulPhi

Model to compute the wet bulb temperature based on relative humidity

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 



Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).


Parameters




TypeNameDefaultDescription


replaceable package MediumModelica.Media.Interfaces.Pa...Medium model


BooleanapproximateWetBulbfalseSet to true to approximate wet bulb temperature




Connectors




TypeNameDescription


replaceable package MediumMedium model


input RealInputTDryBulDry bulb temperature [K]


input RealInputphiRelative air humidity


input RealInputpPressure [Pa]


output RealOutputTWetBulWet bulb temperature [K]




Modelica definition


block TWetBul_TDryBulPhi 
  "Model to compute the wet bulb temperature based on relative humidity"
  extends Modelica.Blocks.Icons.Block;
  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 Real k_mair = 0.6219647130774989 "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=1006 
    "Specific heat capacity of air";
  constant Modelica.SIunits.SpecificHeatCapacity cpSte=1860 
    "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=  Buildings.Utilities.Psychrometrics.Functions.saturationPressureLiquid(TWetBul),
      p=     p,
      phi=   1);
    XiDryBul =Buildings.Utilities.Psychrometrics.Functions.X_pSatpphi(
      p=     p,
      pSat=  Buildings.Utilities.Psychrometrics.Functions.saturationPressureLiquid(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
Buildings.Utilities.Psychrometrics.TWetBul_TDryBulXi



Model to compute the wet bulb temperature based on mass fraction



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





Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).


Parameters




TypeNameDefaultDescription


replaceable package MediumModelica.Media.Interfaces.Pa...Medium model


BooleanapproximateWetBulbfalseSet to true to approximate wet bulb temperature




Connectors




TypeNameDescription


replaceable package MediumMedium model


input RealInputTDryBulDry bulb temperature [K]


input RealInputpPressure [Pa]


output RealOutputTWetBulWet bulb temperature [K]


input RealInputXi[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.Icons.Block;
  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 Real k_mair = 0.6219647130774989 "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=1006 
    "Specific heat capacity of air";
  constant Modelica.SIunits.SpecificHeatCapacity cpSte=1860 
    "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(Buildings.Utilities.Psychrometrics.Functions.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=  Buildings.Utilities.Psychrometrics.Functions.saturationPressureLiquid(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.ToDryAir
Buildings.Utilities.Psychrometrics.ToDryAir



Block to convert absolute humidity from [kg/kg total air] to [kg/kg dry air]



Buildings.Utilities.Psychrometrics.ToDryAir



Information




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




Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).


Connectors




TypeNameDescription


output RealOutputXiDryWater vapor concentration in [kg/kg dry air]


input RealInputXiTotalAirWater 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.Icons.Block;
  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
Buildings.Utilities.Psychrometrics.ToTotalAir



Block to convert absolute humidity from [kg/kg dry air] to [kg/kg total air]



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.




Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).


Connectors




TypeNameDescription


output RealOutputXiTotalAirWater vapor concentration in [kg/kg total air]


input RealInputXiDryWater vapor concentration in [kg/kg dry air]


output RealOutputXNonVaporMass 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.Icons.Block;
  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.WetBul_pTX
Buildings.Utilities.Psychrometrics.WetBul_pTX



Block to compute the wet bulb condition for given dry bulb temperature and humidity



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.




Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).


Connectors




TypeNameDescription


input RealInputTDryBulDry bulb temperature [K]


input RealInputXDryBulDry bulb temperature [1]


input RealInputpPressure [Pa]


output RealOutputTWetBulWet bulb temperature [K]


output RealOutputXWetBulWater 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.Icons.Block;

  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=1006 
    "Specific heat capacity of air";
  constant Modelica.SIunits.SpecificHeatCapacity cpSte=1860 
    "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=   Buildings.Utilities.Psychrometrics.Functions.saturationPressureLiquid(TWetBul),
      p=     p,
      phi=   1);
  TWetBul = (TDryBul * ((1-XDryBul) * cpAir + XDryBul * cpSte) + (XDryBul-XWetBul) * h_fg)/
            ( (1-XWetBul)*cpAir + XWetBul * cpSte);
end WetBul_pTX;







Buildings.Utilities.Psychrometrics.X_pTphi
Buildings.Utilities.Psychrometrics.X_pTphi



Return steam mass fraction as a function of relative humidity phi and temperature T



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.




Extends from Buildings.Utilities.Psychrometrics.BaseClasses.HumidityRatioVaporPressure (Humidity ratio for given water vapor pressure).


Parameters




TypeNameDefaultDescription


Booleanuse_p_intrueGet the pressure from the input connector


Pressurep101325Fixed value of pressure [Pa]




Connectors




TypeNameDescription


input RealInputp_inAtmospheric Pressure [Pa]


input RealInputTTemperature [K]


input RealInputphiRelative humidity (0...1)


output RealOutputX[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.X_pW
Buildings.Utilities.Psychrometrics.X_pW



Humidity ratio for given water vapor pressure



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.




Extends from Buildings.Utilities.Psychrometrics.BaseClasses.HumidityRatioVaporPressure (Humidity ratio for given water vapor pressure).


Parameters




TypeNameDefaultDescription


Booleanuse_p_intrueGet the pressure from the input connector


Pressurep101325Fixed value of pressure [Pa]




Connectors




TypeNameDescription


input RealInputp_inAtmospheric Pressure [Pa]


output RealOutputX_wSpecies concentration at dry bulb temperature


input RealInputp_wWater 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_TDewPoi
Buildings.Utilities.Psychrometrics.pW_TDewPoi



Model to compute the water vapor pressure for a given dew point temperature of moist air



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.




Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).


Connectors




TypeNameDescription


output RealOutputp_wWater vapor partial pressure


input RealInputTDew 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.Icons.Block;
  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.pW_X
Buildings.Utilities.Psychrometrics.pW_X



Water vapor pressure for given humidity ratio



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.




Extends from Buildings.Utilities.Psychrometrics.BaseClasses.HumidityRatioVaporPressure (Humidity ratio for given water vapor pressure).


Parameters




TypeNameDefaultDescription


Booleanuse_p_intrueGet the pressure from the input connector


Pressurep101325Fixed value of pressure [Pa]




Connectors




TypeNameDescription


input RealInputp_inAtmospheric Pressure [Pa]


input RealInputX_wSpecies concentration at dry bulb temperature


output RealOutputp_wWater 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;






Automatically generated Thu Jun 19 11:01:10 2014.