I use variable-speed pumps as much as possible. But they are not a panacea. They can’t achieve their maximum efficiency if you plumb the pool in the traditional way.
In a typical hydraulic layout, the main trunk line from the equipment feeds directly into the loop around the pool, at the point closest to the equipment pad. Back pressure is accumulated by placing smaller returns closest to the pump, then larger returns farther away. When water comes out the trunk line and into the loop, it gets pushed to the left and right, and the back pressure builds up as it passes each of the smaller returns. But this only works if you have a lot of head pressure created by an oversized pump.
To get the most out of a variable-speed pump, you want to run it on the lowest flow possible. But you can’t do that on a typically plumbed pool. The lower horsepower won’t create the needed back pressure, so you’ll have water coming out of the returns closest to the pump, but none out of the farthest returns.
I solve this by using larger plumbing and adding a circulation manifold between the main trunk line and the loop around the pool. The manifold branches off from the trunk line in either direction, then feeds into the loop on each side of the pool at the mid-point between the nearest and farthest returns. This allows for more even distribution of the water and doesn’t require the flow rates to be as high, and we can use the same size returns all the way around the pool.
— Steve Toth, owner, Acclaim Pools, LLC, The Woodlands, Texas