GetRelHumFromTWetBulb Function

  function GetRelHumFromTWetBulb(TDryBulb, TWetBulb, Pressure) result(RelHum)
    !+ Return relative humidity given dry-bulb temperature, wet bulb temperature and pressure.
    !+ References:
    !+ ASHRAE Handbook - Fundamentals (2017) ch. 1

    real, intent(in)  ::  TDryBulb
      !+ Dry-bulb temperature in °F [IP] or °C [SI]
    real, intent(in)  ::  TWetBulb
      !+ Wet-bulb temperature in °F [IP] or °C [SI]
    real, intent(in)  ::  Pressure
      !+ Atmospheric pressure in Psi [IP] or Pa [SI]
    real              ::  RelHum
      !+ Relative humidity in range [0, 1]
    real              ::  HumRatio
      !+ Humidity ratio in lb_H₂O lb_Air⁻¹ [IP] or kg_H₂O kg_Air⁻¹ [SI]

    if (TWetBulb > TDryBulb) then
      error stop "Error: wet bulb temperature is above dry bulb temperature"
    end if

    HumRatio = GetHumRatioFromTWetBulb(TDryBulb, TWetBulb, Pressure)
    RelHum   = GetRelHumFromHumRatio(TDryBulb, HumRatio, Pressure)
  end function GetRelHumFromTWetBulb