Can a PSA tender set a maximum kWh per cubic metre?

What the agency documents ask for

• WHO (December 2024): for the products on offer, the vendor is to indicate the estimated total power consumption, the back-up power supply size required and the peak current during start-up. Among the energy saving components of the air feed compressor, the table lists a variable speed drive (or variable frequency drive) and a soft-starter to reduce the load at start-up.
• UNDP (REQ-OXY-001, effective 1 January 2025): specifications must address critical parameters such as flow rate, purity, pressure, energy efficiency and compatibility with existing systems, and should be reviewed by the Global Fund Partnership and Health Systems Team (GFPHST) quality assurance team. UNDP's site checklist asks whether the plant's power consumption was calculated, including lighting, and the diesel generator sized on the result.
• WHO's Foundations of medical oxygen systems (2023): the energy efficiency of PSA plants is largely determined by the feed air compressor, and peak power demand by the inflow current and voltage of the feed air compressors; where variable speed drive compressors are chosen to reduce peak power, the reliability of the power supply must be carefully assessed first.

Each figure comes with its conditions

PATH and CHAI (July 2021) say that, although there can be notable variation, a conventional PSA plant requires approximately 1.2 kWh per Nm³ produced at 65 psig, depending on system efficiency and oxygen service pressure, and that energy consumption increases for higher service pressures and when cylinders are filled. A Global Fund briefing note (3 April 2024) explains that a plant set to 95 ± 1% purity would need larger equipment than a 93 ± 3% plant to achieve the same flow, with increased operating expenses from the increased power consumption. UNDP notes that VSA and VPSA plants offer lower power consumption, particularly for larger production capacities. For the published figures, see how much electricity a PSA plant uses.

Evidence and cost of ownership

UNDP asks for official performance test reports for key parameters of oxygen generators, including purity, flow and pressure. WHO (2024) asks for tests conducted and documented under the manufacturer's protocols and at least 72 hours of continuous operation to test the entire system before commissioning. WHO's Foundations (2023) says procurement specifications should consider the life cycle and total cost of ownership, and the Global Fund quality assurance policy (amended 15 November 2023) asks for competitive processes that take total cost of ownership into account. PATH and CHAI (October 2021) cite an internal analysis in which electricity represents approximately 50 percent of annual PSA plant operating costs and can equal as much as one-third of the initial capital cost of a new plant.

Ultra Controlo

The ULTRAOX datasheet (2022) states that every 1 bar increase in compressor pressure adds 7% to total electricity consumption, and that if the system is not calculated correctly more than 20% of the installed power is consumed when the compressor switches out of its load cycle. The ULTRASCREW datasheet rates its variable speed version at up to 35% energy savings.