GetDryAirVolume Function

  function GetDryAirVolume(TDryBulb, Pressure) result(DryAirVolume)
    !+ Return dry-air volume given dry-bulb temperature and pressure.
    !+ 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.

    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              ::  DryAirVolume
      !+ Dry air volume in ft³ lb⁻¹ [IP] or in m³ kg⁻¹ [SI]

    if (isIP()) then
      DryAirVolume = GetTRankineFromTFahrenheit(TDryBulb) * R_DA_IP / (144 * Pressure)
    else
      DryAirVolume = GetTKelvinFromTCelsius(TDryBulb) * R_DA_SI / Pressure
    end if
  end function GetDryAirVolume