When to run VS pump at higher RPM

[JamesW]

If we look just at the plumbing and assume a worst case scenario with a single PVC pipe 100 foot long (equivalent length) for suction and return, I get the following for the plumbing part.

1.5” PVC pipe. 0.01144F^2

2” PVC pipe. 0.003129F^2

2.5” PVC pipe. 0.00126F^2

So, it would appear that the plumbing is not that significant.

In most cases, the plumbing will be less than 100 feet for suction or return and there will usually be more than 1 suction and return.

Curves A, B and C are defined by their formulas.

It probably does not make sense to say that a defined curve is necessarily related to the plumbing size.

The real problem is with the equipment like a heat pump that is about H = 0.00628F^2 by itself

This heater is about H = 0.00333F^2

This filter is H = 0.00155F^2

These sand filters are about

S180T ....H = 0.0138F^2

S244T....H = 0.00862F^2

S310T....H = 0.00342F^2

https://www.hayward-pool.com/assets/documents/pools/pdf/manuals/IS210T.pdf

y = 0.00139x^2 for this Nautilus DE filter.

y = 0.00139x^2, x from 0 to 120, y = 0 to 25 - Wolfram|Alpha

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[JamesW]

I think that part of the logic for saying curve B is 1.5” plumbing is not just the plumbing, but the rest of the equipment also tends to be restrictive as well.

For example, a pool with a 100 foot long 1.5” suction and return with an S180T sand filter and a heat pump would have a system curve of about H= 0.03152F^2.

As long as the builder follows the rule of keeping the velocity below 6 feet per second on the suction and below 8 feet per second on the return side, the plumbing should not be an issue.

In my opinion, there are still significant improvements that need to be made to restrictive equipment like heaters, heat pumps, sand filters, multiports etc.

 

[mas985]

Yes, you can always find extreme setups that might match their definitions but these are not typical. For typical plumbing setups, and by that I mean the majority of plumbing systems that I have modeled over the years, the definitions that I use seem to be fairly representative.