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.

Package Content

NameDescription
Buildings.Utilities.Psychrometrics.Functions Functions Package with psychrometric functions
Buildings.Utilities.Psychrometrics.Tdp_pW Tdp_pW Model to compute the dew point temperature for given water vapor pressure of moist air
Buildings.Utilities.Psychrometrics.pW_Tdp pW_Tdp Model to compute the water vapor pressure for a given dew point temperature of moist air
Buildings.Utilities.Psychrometrics.X_pW X_pW Humidity ratio for given water vapor pressure
Buildings.Utilities.Psychrometrics.pW_X pW_X Water vapor pressure for given humidity ratio
Buildings.Utilities.Psychrometrics.X_pTphi X_pTphi Return steam mass fraction as a function of relative humidity phi and temperature T
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.Twb_TdbXi Twb_TdbXi Model to compute the wet bulb temperature
Buildings.Utilities.Psychrometrics.Examples Examples Collection of models that illustrate model use and test models
Buildings.Utilities.Psychrometrics.BaseClasses BaseClasses Library with base classes for psychrometric classes


Buildings.Utilities.Psychrometrics.Tdp_pW Buildings.Utilities.Psychrometrics.Tdp_pW

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

Buildings.Utilities.Psychrometrics.Tdp_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.Interfaces.BlockIcon (Basic graphical layout of input/output block).

Connectors

TypeNameDescription
input RealInputp_wWater vapor partial pressure
output RealOutputTDew point temperature [K]

Modelica definition

block Tdp_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_Tdp(T=T);
end Tdp_pW;

Buildings.Utilities.Psychrometrics.pW_Tdp Buildings.Utilities.Psychrometrics.pW_Tdp

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

Buildings.Utilities.Psychrometrics.pW_Tdp

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.Interfaces.BlockIcon (Basic graphical layout of input/output block).

Connectors

TypeNameDescription
output RealOutputp_wWater vapor partial pressure
input RealInputTDew point temperature [K]

Modelica definition

block pW_Tdp 
  "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_Tdp(T=T);
end pW_Tdp;

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) "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 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;

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

Connectors

TypeNameDescription
input RealInputp_inAtmospheric Pressure [Pa]
replaceable package MediumMedium model
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;
 replaceable package Medium =
      Modelica.Media.Interfaces.PartialCondensingGases "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](min = 0, 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";

initial algorithm 
  i_w :=1;
    for i in 1:Medium.nXi loop
      if Modelica.Utilities.Strings.isEqual(Medium.substanceNames[i], "Water") then
        i_w :=i;
      end if;
    end for;
  i_nw := if i_w == 1 then 2 else 1;
algorithm 
  psat := Medium.saturationPressure(T);
  X[i_w] := phi*k/(k*phi+p_in_internal/psat-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.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.Interfaces.BlockIcon (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.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 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.Interfaces.BlockIcon (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.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.Twb_TdbXi Buildings.Utilities.Psychrometrics.Twb_TdbXi

Model to compute the wet bulb temperature

Buildings.Utilities.Psychrometrics.Twb_TdbXi

Information


Given a moist are medium model, this component computes the states of the medium at its wet bulb temperature.

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

Extends from Modelica.Blocks.Interfaces.BlockIcon (Basic graphical layout of input/output block).

Connectors

TypeNameDescription
input RealInputTdbDry bulb temperature [K]
input RealInputpPressure [Pa]
output RealOutputTwbWet bulb temperature [K]
input RealInputXi[Medium.nXi]Species concentration at dry bulb temperature

Modelica definition

block Twb_TdbXi "Model to compute the wet bulb temperature"
  extends Modelica.Blocks.Interfaces.BlockIcon;
  replaceable package Medium =
    Modelica.Media.Interfaces.PartialCondensingGases "Medium model";

  Modelica.Blocks.Interfaces.RealInput Tdb(
    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 Twb(
    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 
  Medium.BaseProperties dryBul "Medium state at dry bulb temperature";
  Medium.BaseProperties wetBul(Xi(nominal=0.01*ones(Medium.nXi))) 
    "Medium state at wet bulb temperature";
 parameter Integer i_w(min=1, fixed=false) "Index for water substance";
initial algorithm 
  i_w :=1;
    for i in 1:Medium.nXi loop
      if Modelica.Utilities.Strings.isEqual(Medium.substanceNames[i], "Water") then
        i_w :=i;
      end if;
    end for;

equation 
  dryBul.p = p;
  dryBul.T = Tdb;
  dryBul.Xi = Xi;
  wetBul.phi = 1;
  wetBul.p = dryBul.p;
  wetBul.h = dryBul.h + (wetBul.X[i_w] - dryBul.X[i_w])
         * Medium.enthalpyOfLiquid(dryBul.T);
  Twb = wetBul.T;
end Twb_TdbXi;

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