What limits pump size

[Homebrewale]

The general theme for VSP here is to get the largest size you can. Often that means get the 3HP pump over the 1.5HP pump. What sort of limitation on your system (piping, other equipment like filters and heater) prevents you from getting a 3HP pump?

The reason for the above question is that I am working with my pool company to replace my current pump with pump that can pump at a higher volume for a particular RPM. I said I'd like to go to a 3HP pump. Pool guy said there's a reason they installed a 1.5HP pump on your pool. He doesn't know what the piping looks like underground and the equipment installed so he's reluctant to go much larger. He's suggesting a Hayward Tristar 1.85HP.

The things is that all the piping is 2" PVC. The sand filter is Pentair SD80, one of its largest. The heater is a Pentair Mastertemp 400. Current SWG is the iChlor 30 but will be replaced as soon as possible since it is non-functioning. Where would the limitation be on my system to prevent a larger pump?

 

[hexabc]

With 3HP pump you will be nowhere close to running at the maximum speed. You will be able to run your pump at very low RPM, saving money on energy. My pool is about the same size as yours. My 3HP VSP pump primes at 2200 RPM easily, drawing 2.2A current at 240V. A good skimming effect it achieves at 1800 RPM, drawing 1.3A. Most of the time the pump runs at 1600 RPM, drawing only 1A (240W). An alternative, lower power pump, would have to run at higher speeds for the same flow. (According to pump affinity law, the increase of used energy is proportional to the cube of the increase of RPM.)

 

[1poolman1]

The general theme for VSP here is to get the largest size you can. Often that means get the 3HP pump over the 1.5HP pump. What sort of limitation on your system (piping, other equipment like filters and heater) prevents you from getting a 3HP pump?

The reason for the above question is that I am working with my pool company to replace my current pump with pump that can pump at a higher volume for a particular RPM. I said I'd like to go to a 3HP pump. Pool guy said there's a reason they installed a 1.5HP pump on your pool. He doesn't know what the piping looks like underground and the equipment installed so he's reluctant to go much larger. He's suggesting a Hayward Tristar 1.85HP.

The things is that all the piping is 2" PVC. The sand filter is Pentair SD80, one of its largest. The heater is a Pentair Mastertemp 400. Current SWG is the iChlor 30 but will be replaced as soon as possible since it is non-functioning. Where would the limitation be on my system to prevent a larger pump?

Yes, there's a reason they installed a 1.5hp pump. Because they didn't know better and knew that pump would run you spa jets without issues. Builders don't like call-backs. Most pumps in that range, as single-speed pumps, are trying to move at least 110-120GPM.
Maximum recommended flow rate on 2" plumbing (for pool purposes) is 88 GPM. Either of those VSP (1.85 or 2.7) is capable of moving much more than that, even with the added restriction of other pool equipment (filter, etc.). At the pool, the return lines very likely drop down to 1.5" somewhere as that is the standard for return fittings in a residential pool.
The larger the pump in horsepower capability the more water it can move at a certain speed (rpm). The lower you can set that RPM to get the required waterflow the more you save in energy. The difference in cost is usually saved quickly, depending on your cost for electricity.
As installers, we no longer, really, worry about the size of the plumbing as a good VSP can be "dialed in" to get what ever flow required, or to limit to no more than recommended. As goes the saying, "Go big or go home!"

 

[ajw22]

The general theme for VSP here is to get the largest size you can. Often that means get the 3HP pump over the 1.5HP pump. What sort of limitation on your system (piping, other equipment like filters and heater) prevents you from getting a 3HP pump?

The limitation is not on any HP of the pump. The limitation is on the flow rate that pipes can handle before you get diminishing returns with performance.

And it is not about the "pressure" of a higher HP pump damaging pipes or equipment. It does not. Schedule 40 PVC can handle over 100 PSI and no residential pool pumps can push anywhere close to that pressure.

The reason for the above question is that I am working with my pool company to replace my current pump with pump that can pump at a higher volume for a particular RPM. I said I'd like to go to a 3HP pump. Pool guy said there's a reason they installed a 1.5HP pump on your pool. He doesn't know what the piping looks like underground and the equipment installed so he's reluctant to go much larger. He's suggesting a Hayward Tristar 1.85HP.

He is showing single speed pump thinking and does not understand the variable nature of a VS pump.

From Equipment Pad Best Practices - Further Reading

You want to keep the water velocity below 6 ft/sec on the suction and below 8 ft/sec on the pressure side of the pump.

Pipe Size	6 ft/sec	8 ft/sec
1.5"	38 GPM	51 GPM
2"	63 GPM	84 GPM
2.5	90 GPM	119 GPM
3.0"	138 GPM	184 GPM
4.0"	235 GPM	312 GPM

So in the olden days the manufacturers taught to match a single speed pumps HP with the pipe size used. There was no benefit in installing a pump that would push more then 50 GPM with 1.5" pipe or 80 GPM with 2" pipe. There was only one speed and flow rate the pump could run at.

The things is that all the piping is 2" PVC. The sand filter is Pentair SD80, one of its largest. The heater is a Pentair Mastertemp 400. Current SWG is the iChlor 30 but will be replaced as soon as possible since it is non-functioning. Where would the limitation be on my system to prevent a larger pump?

Now with a 3HP VS pump I can run at 1800 RPM and 47 GPM using 400 watts of electricity. If I had a 1.5HP VS pump it would take about 2300 RPM for 47 GPM and use around 800 watts of electricity. And if we were using a 1.5 HP SS pump it would run at about 1400 watts of electricity.

So now we optimize pump selection for the best flow with the least electrical usage. That is a 3+ HP VS pump run slow.

Your system has no limitation to using a VS pump running slow. And if that 3+HP VS pump ran at its maximum rated speed the only thing that would be affected would be your electricity bill.

 

[Homebrewale]

With 3HP pump you will be nowhere close to running at the maximum speed. You will be able to run your pump at very low RPM, saving money on energy. My pool is about the same size as yours. My 3HP VSP pump primes at 2200 RPM easily, drawing 2.2A current at 240V. A good skimming effect it achieves at 1800 RPM, drawing 1.3A. Most of the time the pump runs at 1600 RPM, drawing only 1A (240W). An alternative, lower power pump, would have to run at higher speeds for the same flow. (According to pump affinity law, the increase of used energy is proportional to the cube of the increase of RPM.)

I said I could program the pump to prime at a lower RPM. His response was that all it takes is one person to not know what they're doing and run it at full speed. I really don't see the concern. If you go into the settings to limit the top speed, a clueless person would still need to know how to reprogram it to a higher speed.

 

[JamesW]

The only limit might be your available power supply.

As long as the power supply is sufficient, get the bigger pump.

What is the power supply?

 

[ajw22]

I said I could program the pump to prime at a lower RPM. His response was that all it takes is one person to not know what they're doing and run it at full speed. I really don't see the concern. If you go into the settings to limit the top speed, a clueless person would still need to know how to reprogram it to a higher speed.

What is the burst strength of schedule 40 PVC?

What is the maximum PSI a pool pump can create?

He does not know what he is talking about and spewing nonsense.

 

[JamesW]

The superflo vst can get to about 74 feet of head, which is 32 psi.

The Intelliflo can get to about 86 feet or 37 psi.

So, about 5 psi difference.

Get the bigger pump and set the maximum speed to about 2,400 rpm.

A 15 amp, 240 volt power supply should be sufficient for the intelliflo3.

The IntelliFlo VSF requires a 20 amp 240 volt supply.

 

[Homebrewale]

The only limit might be your available power supply.

As long as the power supply is sufficient, get the bigger pump.

What is the power supply?

230V on a 20 amp breaker.

 

[1poolman1]

I said I could program the pump to prime at a lower RPM. His response was that all it takes is one person to not know what they're doing and run it at full speed. I really don't see the concern. If you go into the settings to limit the top speed, a clueless person would still need to know how to reprogram it to a higher speed.

I have seen a full-rated 3.9 THP single-speed pump on 1.5" plumbing. That was a long time ago, but a 3hp Hayward Super 2 pump could move a lot of water. But it also did damage to the filter and was very noisy.
Regardless of what you my hear, that kind of flow can and did damage to the filter cartridges on a regular basis, crushed them. Customer wouldn't believe me, same reply, "The builder must have seen a reason for this pump."
Saw the same on a 1.5hp Challenger. It kept destroying filter cartridges of a Pac-Fab 160. Had to quit that customer.
On a sand filter it can cause channeling where the water bypasses the sand bed down the sides.
Another, a 1.5 Max-E-Glass kept damaging filter grids. Changed the impeller (down-sized the pump) to a 3/4 and no more issues.
High waterflow rates can strip the copper out of a heat exchanger. On plumbing that can't handle the flow a large pump is also very noisy, and you pay for that noise as it is just wasted energy.
But we no longer worry about those issues with a VSP. Not sure what your service person is trying to do, but he is wrong.
There are precautions that can be taken, if there is doubt, against having a VSP run too fast for the conditions, just set a maximum speed. Or put in a password as many can. Or, with a 2.7 Hayward if that is what you want, don't be concerned as you are going to be the one operating the pump. If the pool service person can't be trusted with your equipment, get a new guy. I've had mine for near 15 years now and have never "accidentally" run it too fast and my pool is plumbed as yours. Nor any pool I have serviced.

 

[JamesW]

Once you get above 20 psi, you can crush cartridges and DE grids.

20 psi is 46 feet of head.

At 67% ( 2,312 RPM), the pressure is limited to 20 psi.

Assuming your system is curve C, you can get to 70 GPM at 2312 rpm.

Assuming Curve A, you can get 50 GPM.

You should never need more than 50 gpm, so set the max speed to 2,300 rpm and you will be safe.

 

[Homebrewale]

Once you get above 20 psi, you can crush cartridges and DE grids.

20 psi is 46 feet of head.

What about sand filters? After I backflush the filter, the pressure on the gauge is 20 psi. While sand should last forever, is this an indication that something is gumming up the sand? Or should I go big or go home on the wallet and replace the sand filter with a cartridge filter while I'm making other changes?

 

[1poolman1]

What about sand filters? After I backflush the filter, the pressure on the gauge is 20 psi. While sand should last forever, is this an indication that something is gumming up the sand? Or should I go big or go home on the wallet and replace the sand filter with a cartridge filter while I'm making other changes?

What is the pressure on "recirc?" That setting will eliminate the sand bed from the water-path and the pressure will be what the rest of the system causes.

 

[Homebrewale]

What is the pressure on "recirc?" That setting will eliminate the sand bed from the water-path and the pressure will be what the rest of the system causes.

Data on the system. gpm measured by Flow-Vis

filter
3450 rpm, 48 gpm, 20 psi
2500 rpm, 30 gpm, 11 psi
2000 rpm 18 gpm, 6.5 psi

recirculate
3450 rpm, 58 gpm, 16 psi
2500 rpm, 35 gpm, 8.5 psi
2000 rpm, 21 gpm, 5.5 psi

 

[1poolman1]

Data on the system. gpm measured by Flow-Vis

filter
3450 rpm, 48 gpm, 20 psi
2500 rpm, 30 gpm, 11 psi
2000 rpm 18 gpm, 6.5 psi

recirculate
3450 rpm, 58 gpm, 16 psi
2500 rpm, 35 gpm, 8.5 psi
2000 rpm, 21 gpm, 5.5 psi

Are those pressure readings something new?

 

[Homebrewale]

Are those pressure readings something new?

Huh? Do you mean recent? They were taken on Monday, 6/10. Pool company wanted me to provide that data. The 2500 and 2000 rpm speeds are presets on the pump. Before the SWG broke, I needed to run 2000 rpm just to keep the SWG on. I backflushed the filter before I took the readings. Filter is when the sand filter is in filtering mode. Currently, no bypass on the heater. Two skimmers on pool. Four returns. Pump about 4' higher than the surface of the water in the pool.

 

[1poolman1]

Huh? Do you mean recent? They were taken on Monday, 6/10. Pool company wanted me to provide that data. The 2500 and 2000 rpm speeds are presets on the pump. Before the SWG broke, I needed to run 2000 rpm just to keep the SWG on. I backflushed the filter before I took the readings. Filter is when the sand filter is in filtering mode. Currently, no bypass on the heater. Two skimmers on pool. Four returns. Pump about 4' higher than the surface of the water in the pool.

Recent as in "Is this a big change from sometime in the past?"

 

[Homebrewale]

Recent as in "Is this a big change from sometime in the past?"

Nope. I'm not the original owner. I bought the house with the pool 2 years ago. Last year, I installed new glycerin filled pressure gauge. It's read 20 psi after backflushing since I installed the gauge. I have no idea what products the previous owner added to the pool. I did a deep clean of the sand back in April when I started up the equipment.

 

[1poolman1]

Nope. I'm not the original owner. I bought the house with the pool 2 years ago. Last year, I installed new glycerin filled pressure gauge. It's read 20 psi after backflushing since I installed the gauge. I have no idea what products the previous owner added to the pool. I did a deep clean of the sand back in April when I started up the equipment.

Those, then, are probably the "normal" readings for your pool. Every pool is a custom pool in the way the plumbing and equipment is installed/plumbed. You can see the added head that having the water go through the sand causes. Not an issue.
You can also see the difference in head as the RPM slows. Each PSI is 2.31 ft. of head. At 3450 your system, with a clean filter, has about 68 ft. of head according to the pump curve for that pump (without a suction gauge that is a good estimate). At 2500 RPM there is only about 30ft. of head.

 

[Homebrewale]

Does that mean you don't see anything of concern? Would installing a larger pump be no problem? Right now I'm working with this pool company since I have a working relationship with them going back to 2006. They sell Hayward equipment. If I wanted to go with Pentair, the main choices are Leslies and an independent company that doesn't have the greatest reviews on Google.