Low Speed Flow Rate

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M

mjdieth

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Sep 21, 2017
34
Pittsburgh/PA
I'm having a hard time figuring out what my flow rate will be on a 1HP 2SP Hayward SuperPump. My pool is scheduled to go in but they have not broken ground yet so I have time to change this if I need to. I want a 2 speed pump for the energy savings, but I'm just not sure what pump will be able to run on low speed and still trigger the heat pump (Pentair UltraTemp 70) which requires at least 30GPM flow to kick on. Since my install has not begun I dont know my head but I can try to explain how the plumbing will work. My 1 skimmer and 1 return will be about 20' from the pump, filter, and heater. This is an IG pool and there is about an 8" grade which the equipment will sit higher than the top of the pool. I should also note that the pool is about 10,000 gallons, I will not have a SWG for now because apparently it will void the warranty on my pool according to the dealer. Equipment listed below:

Hayward SuperPump 1HP 2Speed
Pentair SD60 sand filter
Pentair UltraTemp 70 Heat Pump
IG Radiant Pool @ 10,000 gallons, 4ft depth all over

Thanks for any help you are able to provide me. I really just need to know what pump I will need to buy in order for the heat pump to kick on in low speed.
 
On the Hayward site it states that the high speed produces an output as follows:

20ft Head = 74GPM
30ft Head = 65GPM
40ft Head = 54GPM
50ft Head = 40GPM

anything above that there is no GPM listed.

For low speed it is as follows:

5ft Head = 39GPM
10ft Head = 29GPM
15ft Head = 13GPM

anything above that there is no GPM listed. I guess running on low speed cuts the GPM AND the Head in half, but 13GPM will not run my heat pump, and that is only with 15ft of head as well, which seems low.

This data matches up with the flow curve provided with them. I'm just not sure how to find a pump that will output over 30GPM on low speed. If I have to run on high then it defeats the purpose of the 2 speed pump. I supposed I could go variable speed, but I'm also not sure how much that would save me then either.
 
One thing to keep in mind is all your head calculations will change on the low speed setting. 20 feet of pipe puts up a certain amount of head on high speed, but MUCH LESS on low speed. This will affect how you read the curves.
 
Well, I've done a lot of thinking today and have decided to go with the Pentair SuperFlo 1.5HP VS pump. At least this way I can dial the RPM's down to a point that will allow my heat pump to run on a lower speed than high. Not sure the payoff will be there, but this way I at least have more control of things. I wanted the Intelliflo, however the PB wanted $1800 for the pump (including install). I told them I could get it for half that and they told me they would not install if I did not buy from them, pretty crappy if you ask me.
 
Based upon my reading of hydraulics articles and information on this site, I've come to the conclusion that those pump curves published by the manufacturers bear little, if any, relationship to real life use. For example, at a head pressure above 20 ft, the above table suggests that there will be essentially no flow. Of course, this isn't true. As flow rate goes down, head pressure goes down, so you're chasing your tail trying to calculate flow rate from pump speed and head pressure. There is a differential calculus solution but I don't think you want to get into it that deep!!!

At low speed on a two speed pump, the flow rate should be 1/2 or a little less than full speed in most pools. That may or may not be enough to run a heater, cleaner, waterfall, etc, but the published pump curves won't help you decide.

I think you decision to go with a variable speed pump was probably the right one - you're covered now!

If the resident pump expert (Mark) on this site is around, maybe he can elaborate.
 
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