Flow control and energy

Throttling, on/off, constant pressure and VFD for pumps, fans and compressors.

Try it: four ways to deliver less flow

Flow needed80 %

Throttling valve / damper
On/off cycling
VFD at constant pressure
VFD speed control

Throttling valve / damper: 89 % · 9.66 kW
On/off cycling: 80 % · 8.72 kW (−10 %)
VFD at constant pressure: 80 % · 8.72 kW (−10 %)
VFD speed control: 57 % · 6.21 kW (−36 %)

Lab II network: 120 m³/h at 25 m rated, 5 m static head, pump efficiency held at 75 %. The VFD curve follows the system curve; constant pressure holds 25 m at the pump. On/off cycling also delivers every litre at 25 m, so in this model it costs the same as constant pressure (dotted line), but it needs a tank.