Add functions to convert to dry bulb temperature or humidity ratio from enthalpy

.travis.yml

@@ -18,7 +18,7 @@ install:
 
 script:
   # See https://stackoverflow.com/a/34140498 for why "python -m" is needed.
-  - python -m pytest -v -s
+  - python3 -m pytest -v -s
   - cd tests/js && npm test
   - cd $TRAVIS_BUILD_DIR
 

docs/overview.md

@@ -44,6 +44,8 @@ The following psychrometric functions are currently available across all the sup
 |`GetDryAirEnthalpy`|Return dry-air enthalpy given dry-bulb temperature.|
 |`GetDryAirDensity`|Return dry-air density given dry-bulb temperature and pressure.|
 |`GetDryAirVolume`|Return dry-air volume given dry-bulb temperature and pressure.|
+|`GetTDryBulbFromEnthalpyAndHumRatio`|Return dry bulb temperature from enthalpy and humidity ratio.|
+|`GetHumRatioFromEnthalpyAndTDryBulb`|Return humidity ratio from enthalpy and dry-bulb temperature.|
 |`GetSatVapPres`|Return saturation vapor pressure given dry-bulb temperature.|
 |`GetSatHumRatio`|Return humidity ratio of saturated air given dry-bulb temperature and pressure.|
 |`GetSatAirEnthalpy`|Return saturated air enthalpy given dry-bulb temperature and pressure.|

src/c/psychrolib.c

@@ -610,6 +610,36 @@ double GetDryAirVolume          // (o) Dry air volume ft³ lb⁻¹ [IP] or in m
     return R_DA_SI * GetTKelvinFromTCelsius(TDryBulb) / Pressure;
 }
 
+// Return dry bulb temperature from enthalpy and humidity ratio.
+// Reference: ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 30.
+// Notes: based on the `GetMoistAirEnthalpy` function, rearranged for temperature.
+double GetTDryBulbFromEnthalpyAndHumRatio  // (o) Dry-bulb temperature in °F [IP] or °C [SI]
+  ( double MoistAirEnthalpy                // (i) Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+  , double HumRatio                        // (i) Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
+  )
+{
+  ASSERT (HumRatio >= 0., "Humidity ratio is negative")
+
+  if (isIP())
+    return (MoistAirEnthalpy - 1061.0 * HumRatio) / (0.240 + 0.444 * HumRatio);
+  else
+    return (MoistAirEnthalpy / 1000.0 - 2501.0 * HumRatio) / (1.006 + 1.86 * HumRatio);
+}
+
+// Return humidity ratio from enthalpy and dry-bulb temperature.
+// Reference: ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 30.
+// Notes: based on the `GetMoistAirEnthalpy` function, rearranged for humidity ratio.
+double GetHumRatioFromEnthalpyAndTDryBulb  // (o) Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
+  ( double MoistAirEnthalpy                // (i) Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+  , double TDryBulb                        // (i) Dry-bulb temperature in °F [IP] or °C [SI]
+  )
+{
+  if (isIP())
+    return (MoistAirEnthalpy - 0.240 * TDryBulb) / (1061.0 + 0.444 * TDryBulb);
+  else
+    return (MoistAirEnthalpy / 1000.0 - 1.006 * TDryBulb) / (2501.0 + 1.86 * TDryBulb);
+}
+
 
 /******************************************************************************************************
  * Saturated Air Calculations

src/c/psychrolib.h

@@ -160,18 +160,28 @@ double GetHumRatioFromSpecificHum // (o) Humidity ratio in lb_H₂O lb_Dry_Air
  * Dry Air Calculations
  *****************************************************************************************************/
 
-double GetDryAirEnthalpy        // (o) Dry air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹ [SI]
-  ( double TDryBulb             // (i) Dry bulb temperature in °F [IP] or °C [SI]
+double GetDryAirEnthalpy                  // (o) Dry air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹ [SI]
+  ( double TDryBulb                       // (i) Dry bulb temperature in °F [IP] or °C [SI]
   );
 
-double GetDryAirDensity         // (o) Dry air density in lb ft⁻³ [IP] or kg m⁻³ [SI]
-  ( double TDryBulb             // (i) Dry bulb temperature in °F [IP] or °C [SI]
-  , double Pressure             // (i) Atmospheric pressure in Psi [IP] or Pa [SI]
+double GetDryAirDensity                   // (o) Dry air density in lb ft⁻³ [IP] or kg m⁻³ [SI]
+  ( double TDryBulb                       // (i) Dry bulb temperature in °F [IP] or °C [SI]
+  , double Pressure                       // (i) Atmospheric pressure in Psi [IP] or Pa [SI]
   );
 
-double GetDryAirVolume          // (o) Dry air volume ft³ lb⁻¹ [IP] or in m³ kg⁻¹ [SI]
-  ( double TDryBulb             // (i) Dry bulb temperature in °F [IP] or °C [SI]
-  , double Pressure             // (i) Atmospheric pressure in Psi [IP] or Pa [SI]
+double GetDryAirVolume                    // (o) Dry air volume ft³ lb⁻¹ [IP] or in m³ kg⁻¹ [SI]
+  ( double TDryBulb                       // (i) Dry bulb temperature in °F [IP] or °C [SI]
+  , double Pressure                       // (i) Atmospheric pressure in Psi [IP] or Pa [SI]
+  );
+
+double GetTDryBulbFromEnthalpyAndHumRatio    // (o) Dry-bulb temperature in °F [IP] or °C [SI]
+  ( double MoistAirEnthalpy                  // (i) Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+  , double HumRatio                          // (i) Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
+  );
+
+double GetHumRatioFromEnthalpyAndTDryBulb  // (o) Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
+  ( double MoistAirEnthalpy                // (i) Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+  , double TDryBulb                        // (i) Dry-bulb temperature in °F [IP] or °C [SI]
   );
 
 

src/fortran/psychrolib.f90

@@ -69,6 +69,8 @@ module psychrolib
   public :: GetDryAirEnthalpy
   public :: GetDryAirDensity
   public :: GetDryAirVolume
+  public :: GetTDryBulbFromEnthalpyAndHumRatio
+  public :: GetHumRatioFromEnthalpyAndTDryBulb
   public :: GetSatVapPres
   public :: GetSatHumRatio
   public :: GetSatAirEnthalpy
@@ -821,6 +823,52 @@ function GetDryAirVolume(TDryBulb, Pressure) result(DryAirVolume)
     end if
   end function GetDryAirVolume
 
+  function GetTDryBulbFromEnthalpyAndHumRatio(MoistAirEnthalpy, HumRatio) result(TDryBulb)
+    !+ Return dry bulb temperature from enthalpy and humidity ratio.
+    !+ Reference:
+    !+ ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 30
+    !+ Notes:
+    !+ Based on the `GetMoistAirEnthalpy` function, rearranged for temperature.
+
+    real, intent(in)  ::  MoistAirEnthalpy
+      !+ Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+    real, intent(in)  ::  HumRatio
+      !+ Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
+    real              ::  TDryBulb
+      !+ Dry-bulb temperature in °F [IP] or °C [SI]
+
+    if (HumRatio < 0.0) then
+      error stop "Error: humidity ratio is negative"
+    end if
+
+    if (isIP()) then
+      TDryBulb  = (MoistAirEnthalpy - 1061.0 * HumRatio) / (0.240 + 0.444 * HumRatio)
+    else
+      TDryBulb  = (MoistAirEnthalpy / 1000.0 - 2501.0 * HumRatio) / (1.006 + 1.86 * HumRatio)
+    end if
+  end function GetTDryBulbFromEnthalpyAndHumRatio
+
+  function GetHumRatioFromEnthalpyAndTDryBulb(MoistAirEnthalpy, TDryBulb) result(HumRatio)
+    !+ Return humidity ratio from enthalpy and dry-bulb temperature.
+    !+ Reference:
+    !+ ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 30
+    !+ Notes:
+    !+ Based on the `GetMoistAirEnthalpy` function, rearranged for humidity ratio.
+
+    real, intent(in)  ::  MoistAirEnthalpy
+      !+ Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+    real, intent(in)  ::  TDryBulb
+      !+ Dry-bulb temperature in °F [IP] or °C [SI]
+    real              ::  HumRatio
+      !+ Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
+
+    if (isIP()) then
+      HumRatio  = (MoistAirEnthalpy - 0.240 * TDryBulb) / (1061.0 + 0.444 * TDryBulb)
+    else
+      HumRatio  = (MoistAirEnthalpy / 1000.0 - 1.006 * TDryBulb) / (2501.0 + 1.86 * TDryBulb)
+    end if
+  end function GetHumRatioFromEnthalpyAndTDryBulb
+
 
   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
   ! Saturated Air Calculations

src/js/psychrolib.js

@@ -555,21 +555,49 @@ function Psychrometrics() {
   }
 
   // Return dry-air volume given dry-bulb temperature and pressure.
-  // Reference: ASHRAE Handbook - Fundamentals (2017) ch. 1
+  // Reference: ASHRAE Handbook - Fundamentals (2017) ch. 1.
   // Notes: eqn 14 for the perfect gas relationship for dry air.
   // Eqn 1 for the universal gas constant.
   // The factor 144 in IP is for the conversion of Psi = lb in⁻² to lb ft⁻².
   this.GetDryAirVolume = function // (o) Dry air volume ft³ lb⁻¹ [IP] or in m³ kg⁻¹ [SI]
     ( TDryBulb                    // (i) Dry bulb temperature in °F [IP] or °C [SI]
     , Pressure                    // (i) Atmospheric pressure in Psi [IP] or Pa [SI]
     ) {
-
     if (this.isIP())
       return R_DA_IP * this.GetTRankineFromTFahrenheit(TDryBulb) / (144. * Pressure);
     else
       return R_DA_SI * this.GetTKelvinFromTCelsius(TDryBulb) / Pressure;
   }
 
+  // Return dry bulb temperature from enthalpy and humidity ratio.
+  // Reference: ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 30.
+  // Notes: based on the `GetMoistAirEnthalpy` function, rearranged for temperature.
+  this.GetTDryBulbFromEnthalpyAndHumRatio = function   // (o) Dry-bulb temperature in °F [IP] or °C [SI]
+    ( MoistAirEnthalpy                                 // (i) Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+    , HumRatio                                         // (i) Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
+    ) {
+    if (!(HumRatio >= 0.))
+      throw new Error("Humidity ratio is negative");
+
+    if (this.isIP())
+      return (MoistAirEnthalpy - 1061.0 * HumRatio) / (0.240 + 0.444 * HumRatio);
+    else
+      return (MoistAirEnthalpy / 1000.0 - 2501.0 * HumRatio) / (1.006 + 1.86 * HumRatio);
+    }
+
+  // Return humidity ratio from enthalpy and dry-bulb temperature.
+  // Reference: ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 30.
+  // Notes: based on the `GetMoistAirEnthalpy` function, rearranged for humidity ratio.
+  this.GetHumRatioFromEnthalpyAndTDryBulb = function   // (o) Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻
+    ( MoistAirEnthalpy                                 // (i) Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+    , TDryBulb                                         // (i) Dry-bulb temperature in °F [IP] or °C [SI]
+    ) {
+    if (this.isIP())
+      return (MoistAirEnthalpy - 0.240 * TDryBulb) / (1061.0 + 0.444 * TDryBulb);
+    else
+      return (MoistAirEnthalpy / 1000.0 - 1.006 * TDryBulb) / (2501.0 + 1.86 * TDryBulb);
+    }
+
 
   /******************************************************************************************************
    * Saturated Air Calculations

src/python/psychrolib.py

@@ -44,6 +44,7 @@
 
 import math
 from enum import Enum, auto
+from typing import Optional
 
 
 #######################################################################################################
@@ -119,7 +120,7 @@ def SetUnitSystem(Units: UnitSystem) -> None:
     else:
         PSYCHROLIB_TOLERANCE = 0.001
 
-def GetUnitSystem() -> UnitSystem:
+def GetUnitSystem() -> Optional[UnitSystem]:
     """
     Return system of units in use.
 
@@ -799,6 +800,60 @@ def GetDryAirVolume(TDryBulb: float, Pressure: float) -> float:
     return DryAirVolume
 
 
+def GetTDryBulbFromEnthalpyAndHumRatio(MoistAirEnthalpy: float, HumRatio: float) -> float:
+    """
+    Return dry bulb temperature from enthalpy and humidity ratio.
+
+
+    Args:
+        MoistAirEnthalpy : Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+        HumRatio : Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
+
+    Returns:
+        Dry-bulb temperature in °F [IP] or °C [SI]
+
+    Reference:
+        ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 30
+
+    Notes:
+        Based on the `GetMoistAirEnthalpy` function, rearranged for temperature.
+
+    """
+    if HumRatio < 0:
+        raise ValueError("Humidity ratio is negative")
+
+    if isIP():
+        TDryBulb  = (MoistAirEnthalpy - 1061.0 * HumRatio) / (0.240 + 0.444 * HumRatio)
+    else:
+        TDryBulb  = (MoistAirEnthalpy / 1000.0 - 2501.0 * HumRatio) / (1.006 + 1.86 * HumRatio)
+    return TDryBulb
+
+def GetHumRatioFromEnthalpyAndTDryBulb(MoistAirEnthalpy: float, TDryBulb: float) -> float:
+    """
+    Return humidity ratio from enthalpy and dry-bulb temperature.
+
+
+    Args:
+        MoistAirEnthalpy : Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+        TDryBulb : Dry-bulb temperature in °F [IP] or °C [SI]
+
+    Returns:
+        Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
+
+    Reference:
+        ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 30.
+
+    Notes:
+        Based on the `GetMoistAirEnthalpy` function, rearranged for humidity ratio.
+
+    """
+    if isIP():
+        HumRatio  = (MoistAirEnthalpy - 0.240 * TDryBulb) / (1061.0 + 0.444 * TDryBulb)
+    else:
+        HumRatio  = (MoistAirEnthalpy / 1000.0 - 1.006 * TDryBulb) / (2501.0 + 1.86 * TDryBulb)
+    return HumRatio
+
+
 #######################################################################################################
 # Saturated Air Calculations
 #######################################################################################################

src/vba/psychrolib.bas

@@ -917,7 +917,7 @@ Function GetSpecificHumFromHumRatio(ByVal HumRatio As Variant) As Variant
 '     ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 9b
 '
 '
-  Dim SpecificHum as Variant
+  Dim SpecificHum As Variant
 
   On Error GoTo ErrHandler
 
@@ -1065,6 +1065,77 @@ ErrHandler:
 
 End Function
 
+Function GetTDryBulbFromEnthalpyAndHumRatio(ByVal MoistAirEnthalpy As Variant, ByVal HumRatio As Variant) As Variant
+'
+' Return dry bulb temperature from enthalpy and humidity ratio.
+'
+'
+' Args:
+'     MoistAirEnthalpy : Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+'     HumRatio : Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
+'
+' Returns:
+'     Dry-bulb temperature in °F [IP] or °C [SI]
+'
+' Reference:
+'     ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 30
+'
+' Notes:
+'     Based on the `GetMoistAirEnthalpy` function, rearranged for temperature.
+'
+
+  On Error GoTo ErrHandler
+
+  If HumRatio < 0 Then
+    MyMsgBox ("Humidity ratio is negative")
+    GoTo ErrHandler
+  End If
+
+  If (isIP()) Then
+    GetTDryBulbFromEnthalpyAndHumRatio = (MoistAirEnthalpy - 1061.0 * HumRatio) / (0.24 + 0.444 * HumRatio)
+  Else:
+    GetTDryBulbFromEnthalpyAndHumRatio = (MoistAirEnthalpy / 1000.0 - 2501.0 * HumRatio) / (1.006 + 1.86 * HumRatio)
+  End If
+  Exit Function
+
+ErrHandler:
+  GetTDryBulbFromEnthalpyAndHumRatio = CVErr(xlErrNA)
+
+End Function
+
+Function GetHumRatioFromEnthalpyAndTDryBulb(ByVal MoistAirEnthalpy As Variant, ByVal TDryBulb As Variant) As Variant
+'
+' Return humidity ratio from enthalpy and dry-bulb temperature.
+'
+'
+' Args:
+'     MoistAirEnthalpy : Moist air enthalpy in Btu lb⁻¹ [IP] or J kg⁻¹
+'     TDryBulb : Dry-bulb temperature in °F [IP] or °C [SI]
+'
+' Returns:
+'     Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
+'
+' Reference:
+'     ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 30
+'
+' Notes:
+'     Based on the `GetMoistAirEnthalpy` function, rearranged for humidity ratio.
+'
+
+  On Error GoTo ErrHandler
+
+  If (isIP()) Then
+    GetHumRatioFromEnthalpyAndTDryBulb = (MoistAirEnthalpy - 0.24 * TDryBulb) / (1061.0 + 0.444 * TDryBulb)
+  Else:
+    GetHumRatioFromEnthalpyAndTDryBulb = (MoistAirEnthalpy / 1000.0 - 1.006 * TDryBulb) / (2501.0 + 1.86 * TDryBulb)
+  End If
+  Exit Function
+
+ErrHandler:
+  GetHumRatioFromEnthalpyAndTDryBulb = CVErr(xlErrNA)
+
+End Function
+
 
 '******************************************************************************************************
 ' Saturated Air Calculations

tests/js/test_psychrolib_ip.js

@@ -133,6 +133,8 @@ it('test_DryAir', function () {
         checkRelDiff(psyjs.GetDryAirEnthalpy(77), 18.498, 0.001)
         checkRelDiff(psyjs.GetDryAirVolume(77, 14.696), 13.5251, 0.001)
         checkRelDiff(psyjs.GetDryAirDensity(77, 14.696), 1/13.5251, 0.001)
+        expect(psyjs.GetTDryBulbFromEnthalpyAndHumRatio(42.6168, 0.02)).to.be.closeTo(86, 0.05)
+        checkRelDiff(psyjs.GetHumRatioFromEnthalpyAndTDryBulb(42.6168, 86), 0.02, 0.001)
 });
 
 

tests/js/test_psychrolib_si.js

@@ -133,6 +133,8 @@ it('test_DryAir', function () {
         checkRelDiff(psyjs.GetDryAirEnthalpy(25), 25148, 0.0003)
         checkRelDiff(psyjs.GetDryAirVolume(25, 101325), 0.8443, 0.001)
         checkRelDiff(psyjs.GetDryAirDensity(25, 101325), 1/0.8443, 0.001)
+        expect(psyjs.GetTDryBulbFromEnthalpyAndHumRatio(81316, 0.02)).to.be.closeTo(30, 0.001)
+        checkRelDiff(psyjs.GetHumRatioFromEnthalpyAndTDryBulb(81316, 30), 0.02, 0.001)
 });
 
 

tests/test_psychrolib_ip.py

@@ -109,6 +109,8 @@ def test_DryAir(psy):
     assert psy.GetDryAirEnthalpy(77) == pytest.approx(18.498, rel = 0.001)
     assert psy.GetDryAirVolume(77, 14.696) == pytest.approx(13.5251, rel = 0.001)
     assert psy.GetDryAirDensity(77, 14.696) == pytest.approx(1/13.5251, rel = 0.001)
+    assert psy.GetTDryBulbFromEnthalpyAndHumRatio(42.6168, 0.02) == pytest.approx(85.97, abs = 0.05)
+    assert psy.GetHumRatioFromEnthalpyAndTDryBulb(42.6168, 86) == pytest.approx(0.02, rel = 0.001)
 
 
 ###############################################################################