GetSatHumRatio Function

  function GetSatHumRatio(TDryBulb, Pressure) result(SatHumRatio)
    !+ Return humidity ratio of saturated air given dry-bulb temperature and pressure.
    !+ Reference:
    !+ ASHRAE Handbook - Fundamentals (2017) ch. 1 eqn 36, solved for W

    real, intent(in)  ::  TDryBulb
      !+ Dry-bulb temperature in °F [IP] or °C [SI]
    real, intent(in)  ::  Pressure
      !+ Atmospheric pressure in Psi [IP] or Pa [SI]
    real              ::  SatHumRatio
      !+ Humidity ratio of saturated air in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]
    real              ::  SatVaporPres
      !+ Vapor pressure of saturated air in in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]

    SatVaporPres  = GetSatVapPres(TDryBulb)
    SatHumRatio   = 0.621945 * SatVaporPres / (Pressure-SatVaporPres)

    ! Validity check.
    SatHumRatio = max(SatHumRatio, MIN_HUM_RATIO)
  end function GetSatHumRatio