How does humidity affect a PSA oxygen plant?

WHO's Technical specifications for PSA oxygen plants (interim guidance, 8 June 2020) asked for plants capable of supplying the specified oxygen concentration continuously at ambient temperatures of 10 to 40 °C and relative humidity of 15 to 95%, preferably simultaneously, at elevations from 0 to 1000 m, as a minimum. The PATH and CHAI brief (July 2021) gives the same temperature and humidity ranges, with elevation from 0 to at least 2,000 m. WHO's Foundations of medical oxygen systems (2023) asks for site conditions such as elevation, temperature, humidity and dust to be addressed at the design phase.

Where the water goes

• Compression: a Global Fund briefing note (4 March 2025) explains that a PSA plant needs an air dryer because moisture in the air condenses at high pressures.
• Drying and filtration: WHO (2023) describes the compressed air passing through a filtration assembly that removes particulate matter and remaining moisture before it reaches the zeolite molecular sieve. A USAID RISE operating procedure says dried air eliminates operational issues in the molecular sieves and solenoid valve, and asks operators to make sure the air entering the adsorption towers is dried and filtered.
• Drains: the same procedure has operators open the air tank and filter drains during start-up to check for water, and not let air into the generator if water appears; it forbids running the plant with automatic drain valves that do not drain properly.
• Monitoring: WHO's 2020 specifications asked for an alarm when the air dryer pressure dew point rises above 3 °C. AIGA 113/20 asks for moisture analysers connected to the control and alarm systems, so that the main shut-off valve may close automatically if impurities exceed the pharmacopoeia specification.

The room and the site

AIGA 113/20 asks for a ventilation or air conditioning system that keeps the temperature and humidity of the plant room within the manufacturer's operating range, and notes that compressor throughput also depends on altitude. Among the oxygen generation technologies, UNDP's technical and regulatory requirements for oxygen plants (effective 1 January 2025) credit VSA, which uses a blower and vacuum pump, with longer sieve life and better efficiency in humid conditions.

ULTRAOX plants treat the compressed air with a water separator with electronic drain, high efficiency micro and sub-micro filters, an activated carbon filter and an air quality control system, and the 2022 datasheet includes the ULTRASEC refrigeration dryer with a digital dew point indicator and automatic condensate evacuation. The ULTRACON concentrator removes contaminants such as H2O and CO2 by adsorption. The ULTRAOX 2022 datasheet asks for ambient air at an acceptable level of humidity and states that, in good conditions, the zeolite can last up to 10 years or more without replacement.