# How much energy can a variable speed compressor save?

**How much energy can a variable speed drive save on a compressed air system?**

A variable speed drive saves energy by matching compressor motor speed to air demand, so the saving depends on how much the demand varies; for its ULTRASCREW VSD compressors, Ultra Controlo states energy savings of up to 35%.

A [VSD](https://library.ultracontrolo.com/glossary/vsd/) changes the speed of the compressor motor to follow demand and keeps the output pressure constant. How much it saves depends on the site's demand profile, so there is no single figure that applies to every installation. The ULTRASCREW datasheet states its figure as an upper value.

## What the ULTRASCREW datasheet says

- Up to 35% energy savings for the variable speed version.
- Operation at constant output pressure, over a wide pressure range of 5 to 14 bar.
- Smooth start of the compressor and protection against the effects of power surges.
- High efficiency IE3 IP55 electric motors.

ULTRASCREW is an oil-injected rotary screw compressor range, not an oil-free machine.

## Pressure also costs energy

Running a compressor at a higher pressure than the network needs also costs power. The ULTRASEC datasheet estimates that an increase of 1 bar on the compressor costs about 7% of the installed motor power.

## VSD in medical air plants

HTM 02-01 (2026) says all medical air plant designs should consider VSD compressors, and that a single dual-purpose plant for medical and surgical air with VSDs should be specified as the most sustainable and efficient solution. Where a VSD compressor provides the primary control of demand, it should be sized to no more than 80% of the required flow rate. The HTM also requires a minimum plant efficiency of 5 m³/kWh at 100% and 10% of design flow.

### Is the 35% figure guaranteed?

No. The ULTRASCREW datasheet states up to 35%, which is a maximum rather than a figure for every installation.

### Should hospitals use VSD compressors for medical air?

HTM 02-01 (2026) says all medical air plant designs should consider VSD compressors.

## Sources

- [ULTRASCREW datasheet, p. 2](https://www.ultracontrolo.com/products/ultrascrew-ds-vsd)
- [ULTRASEC datasheet, p. 2](https://www.ultracontrolo.com/products/ultrasec)
- [NHS England, HTM 02-01 Medical gas pipeline systems (2026), Part A, 7.2, 7.6, 7.10 and 7.43](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-a-design-installation-validation-verification-aug-2026.pdf)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/how-much-can-a-vsd-compressor-save/