Originally Posted by
MrFreez717
Not true for compressors.
Centrifugal pumps and fans, yes.
Gear drive pumps, no.
For centrifugal pumps, flow varies linearly with pump speed. Pressure varies by the inverse square of the speed ratio (1/2 speed will yield 1/4 the original pressure). Power varies with the inverse cube of the speed ratio. So at half speed, your pump will (theoretically) use 1/8 as much power as it would at full speed.
Obviously there is tremendous potential for energy savings because of this, but there are 2 challenges to overcome: 1) significantly reduced pump pressure at lower speeds, which moves you to a different and possibly less efficient point on the pump curve. And 2) changing flow rate changes work done by the chiller, and it can be challenging for expansion valves to adapt and still maintain steady superheat. Electronic valves are your best bet if you try this. You would certainly want to consider appropriate protection against freeze-up as well.
With most fans, VFDs are close to a no-brainer. For pumps, it is not nearly as easy to determine if a VFD is a good idea.
In my part of the US, most power providers will provide incentives for installations of VFDs, particularly on fan motors.
Best regards,
MrFreez717