Buildings.Utilities.Psychrometrics

Package Content

Name	Description
DewPointTemperature	Model to compute the dew point temperature of moist air
Examples	Collection of models that illustrate model use and test models
HumidityRatioPressure	Relation between humidity ratio and water vapor pressure
WetBulbTemperature	Model to compute the wet bulb temperature

Buildings.Utilities.Psychrometrics.DewPointTemperature

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
RealSignal	p_w	Water vapor partial pressure
RealSignal	T	Dew point temperature

Modelica definition

model DewPointTemperature 
  "Model to compute the dew point temperature of moist air" 
 extends Buildings.BaseClasses.BaseIcon;
  Modelica.Blocks.Interfaces.RealSignal p_w(redeclare type SignalType = 
        Modelica.SIunits.Pressure (
        min=0,
        start=10000,
        nominal=10000)) "Water vapor partial pressure";
  Modelica.Blocks.Interfaces.RealSignal T(redeclare type SignalType = 
        Modelica.SIunits.Temperature (
        min=200,
        max=400,
        start=283.15,
        nominal=100)) "Dew point temperature";
protected 
  constant Real C8 = -5.800226E3;
  constant Real C9 =  1.3914993E0;
  constant Real C10= -4.8640239E-2;
  constant Real C11 = 4.1764768E-5;
  constant Real C12= -1.4452093E-8;
  constant Real C13 = 6.5459673E0;
equation 
 p_w = Modelica.Math.exp(C8/T + C9 + T * ( C10
           + T * ( C11 + T * C12))  + C13 * Modelica.Math.log(T));
end DewPointTemperature;

Buildings.Utilities.Psychrometrics.HumidityRatioPressure

Information

Model to compute the relation between humidity ratio and water vapor partial pressure of moist air.

Parameters

Type	Name	Default	Description
Pressure	pAtm	101325	Fixed value of pressure [Pa]

Connectors

Type	Name	Description
RealSignal	p	Pressure
RealSignal	XWat	Species concentration at dry bulb temperature
RealSignal	p_w	Water vapor pressure

Modelica definition

model HumidityRatioPressure 
  "Relation between humidity ratio and water vapor pressure" 
  extends Buildings.BaseClasses.BaseIcon;
  parameter Modelica.SIunits.Pressure pAtm = 101325 "Fixed value of pressure";
  Modelica.Blocks.Interfaces.RealSignal p(redeclare type SignalType = 
        Modelica.SIunits.Pressure (start=101325, nominal=100000)) "Pressure";
  Modelica.Blocks.Interfaces.RealSignal XWat(redeclare type SignalType = 
        Modelica.SIunits.MassFraction (start=0.01), nominal=0.01) 
    "Species concentration at dry bulb temperature";
  Modelica.Blocks.Interfaces.RealSignal p_w(redeclare type SignalType = 
        Modelica.SIunits.Pressure (
        start=10000,
        nominal=10000,
        min=0)) "Water vapor pressure";
  
  Modelica.SIunits.MassFraction X_dryAir(min=0, max=1, nominal=0.01, start=0.001) 
    "Water mass fraction per mass of dry air";
equation 
  if cardinality(p)==0 then
    p = pAtm;
  end if;
  X_dryAir * (1-XWat) = XWat;
 ( p - p_w)   * X_dryAir = 0.62198 * p_w;
end HumidityRatioPressure;

Buildings.Utilities.Psychrometrics.WetBulbTemperature

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.Fluids.Sensors.WetBulbTemperature

Connectors

Type	Name	Description
RealSignal	TDryBul	Dry bulb temperature
RealSignal	p	Pressure
RealSignal	TWetBul	Wet bulb temperature
RealSignal	X[Medium.nX]	Species concentration at dry bulb temperature
RealSignal	phi	Relative humidity (at dry-bulb state) in [0, 1]

Modelica definition

model WetBulbTemperature "Model to compute the wet bulb temperature" 
  extends Buildings.BaseClasses.BaseIcon;
  replaceable package Medium = 
    Modelica.Media.Interfaces.PartialMedium "Medium model";
  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";
  Modelica.Blocks.Interfaces.RealSignal TDryBul(redeclare type SignalType = 
        Modelica.SIunits.Temperature (start=293.15, min=150, max=373)) 
    "Dry bulb temperature";
  Modelica.Blocks.Interfaces.RealSignal p(redeclare type SignalType = 
        Modelica.SIunits.Pressure (start=101325, nominal=100000)) "Pressure";
  Modelica.Blocks.Interfaces.RealSignal TWetBul(redeclare type SignalType = 
        Modelica.SIunits.Temperature (start=283.15, min=150, max=350)) 
    "Wet bulb temperature";
  Modelica.Blocks.Interfaces.RealSignal X[Medium.nX](redeclare type SignalType 
      = 
       Medium.MassFraction) "Species concentration at dry bulb temperature";
  Modelica.Blocks.Interfaces.RealSignal phi(redeclare type SignalType = Real (
        start=0.5,
        min=0,
        max=1)) "Relative humidity (at dry-bulb state) in [0, 1]";
equation 
  dryBul.p = p;
  dryBul.T = TDryBul;
  dryBul.Xi = X[1:Medium.nXi];
  wetBul.phi = 1;
  wetBul.p = dryBul.p;
  wetBul.h = dryBul.h + (wetBul.X[Medium.Water] - dryBul.X[Medium.Water])
         * Medium.enthalpyOfLiquid(dryBul.T);
  TWetBul = wetBul.T;
  phi     = dryBul.phi;
end WetBulbTemperature;