Abstract: The present invention utilizes a membrane cartridge that removes water vapor or fluid from air that passes through the cartridge. The longer the air remains within the cartridge, the more fluid is removed from the air. Consequently, as the air becomes "drier", the dew point temperature of the air also falls. The present invention permits decreases in the flow rate and system pressure while providing dehumidified air with the desired dew point temperature. These decreases in pressure and flow rate result from increased elevation or system wear. The decrease in system pressure and flow rate increases the residence time of the air in the membrane cartridge. As a result, the dew point temperature of the dehumidified air remains stable because increased residence time increases the amount of fluid removed from the air, which tends to reduce the dew point temperature of the dehumidified air.