GetHumRatioFromEnthalpyAndTDryBulb Function

  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

    ! Validity check.
    HumRatio = max(HumRatio, MIN_HUM_RATIO)
  end function GetHumRatioFromEnthalpyAndTDryBulb