Replumbing pool

benny_terry · Jul 23, 2011

Hello everyone,
I am in the midst of a pool remodel, and since I am very new to the world of pool building and maintenance, thought I would pass the plans by everyone and get a few ideas. The pool is a 16'x32' gunite which had a leaking main drain and a single 1/2" copper return. It was terribly neglected, but I am determined to renovate it fully and use it.
Here are some highlights of the plan.

Drilled three 3" drain holes in pool, installed two skimmers. Sealed main drain because there was no way to dig under pool and replace plumbing.
Drilled three 3" feed holes in pool.
Relocated pump and equipment to an area four feet away from pool, now pump, filter, etc is located three feet below the top of the water.
Connected all 3" feeds/returns to 4" ABS pipe. 4" pipe steps down to 2.5" at the pump station to accomodate pump impeller housing.
Pump is a three-phase 56 frame 220v A.O. Smith 3hp motor with a variable speed controller and a network communication card which will allow me to program pump speeds via network. Currently shopping for a wet end that will connect to the A.O. motor. It is my understanding that the three phase motor will both be more efficient and also allow me to have endless control over pump speed, all at about half of the price of a true variable speed single phase pump - anyone else had any experience with this?
Filter is the Hayward DE4820.
Changing over to salt and UV at the recommendation of a knowledgeable friend. Looking for recommendations on a salt generator and UV sterilizer.
The plaster finish is in really bad shape, so I have plans to use SpectraQuartz "F" with an epoxy resin. I wanted to do pebbletec, but my wife hated the feeling on her feet.

I have currently trenched around the pool, set the skimmers and sealed the 3" ABS drain/return rings in the pool and I am getting ready to plumb everything. In reading hydraulics 101, I understand that perhaps it would be better to connect the pool return jets in a large continuous circle, rather than a branch of three returns with a dead-end at the last jet. Essentially the trench is complete around the whole pool, so it would only mean 40 extra feet of 4" pipe, so no big deal. My thinking is that it would equalize pressure to all three jets, is this correct logic?

Thanks in advance, please remember that I am a newbie to pools, but not to plumbing or renovation, so any thoughts are very helpful, and appreciated.

JasonLion · Jul 23, 2011

Welcome to TFP!

How large is your pool? For just about any residential pool, 4" pipe is overkill. It shouldn't hurt, but it doesn't help all that much either.

Not all three phase motors will work well with variable speed controllers. Make sure your motor is suitable for inverter duty or is MG-31 rated.

Looping the pipe will equalize the returns.

UV isn't generally worth getting for outdoor residential pools. UV is good at removing CC, but unless you have a fairly high bother load (think commercial pool) chlorine and sunlight together get rid of CC before the UV has a chance to so there is no benefit to having the UV system.

mas985 · Jul 23, 2011

benny_terry said:
Pump is a three-phase 56 frame 220v A.O. Smith 3hp motor with a variable speed controller and a network communication card which will allow me to program pump speeds via network. Currently shopping for a wet end that will connect to the A.O. motor. It is my understanding that the three phase motor will both be more efficient and also allow me to have endless control over pump speed, all at about half of the price of a true variable speed single phase pump - anyone else had any experience with this?

Do you have access to three phase power? The difference in efficiency is not all that much so I would not go to the trouble of using a three phase motor unless you are planning to use a variable frequency drive. But then it might be better to just go with a variable speed pump which will be much more efficient that just a 3 phase motor.

I have currently trenched around the pool, set the skimmers and sealed the 3" ABS drain/return rings in the pool and I am getting ready to plumb everything. In reading hydraulics 101, I understand that perhaps it would be better to connect the pool return jets in a large continuous circle, rather than a branch of three returns with a dead-end at the last jet. Essentially the trench is complete around the whole pool, so it would only mean 40 extra feet of 4" pipe, so no big deal. My thinking is that it would equalize pressure to all three jets, is this correct logic?

I suspect that the 4" pipe will act more like a header so most of the head loss will be in the eyeballs themselves and a loop may not help very much.

Instead of 4" pipe you might consider multiple runs of 2" or 2.5" pipe. It is easier to work with and much easier to find. 6 runs of 2" pipe has about the same head loss as a single 4" pipe and 4 runs of 2.5" pipe are better than a 4" pipe. Just something to consider.

BTW, why are you using ABS and is it pressure rated?

benny_terry · Jul 24, 2011

Hello everyone,

The pool is 21k gallons.
The rationale behind putting the three-phase motor with a VFD is that I can control and program the pump speed by tying it into my home automation system (Crestron). The VFD changes the single-phase electricity to three-phase, and allows programming and network capability. All this for about $270, paired to a motor that cost me about $100.

I am using ABS because I had to run new sewer lines in the midst of the renovation project. I have a lot of extra schedule 40 that I bought at the same price the pool supply place wants for the 2.5". I've also noticed that the fittings that are available for the ABS - most notably the long-sweep wye result in a longer transition to 90 degrees, and in my thinking, potentially could contribute to lower resistance and head. Not much, I know.

Thanks for the comments about the UV. I could probably add it later if I find the need to.

Does anyone have a SWG that they can recommend?

mas985 · Jul 24, 2011

I would not use DWV rated (drain, waste and vent) ABS pipe for pool plumbing. While you might get away with it, there is still a risk.

Is a 3-phase motor that costs only $100 rated for inverter duty? Also, are you planning to use a matched shielded cable between the motor and VFD?

benny_terry · Jul 25, 2011

Hi Mark,
Not sure I understand why sched. 40 ABS would be a bad thing to use. On this link http://www.ridgidforum.com/forum/attach ... atings.doc
it looks like the schedule 40 Abs that i am using can withstand substantial pressures. Does the standard product that one uses for pool plumbng (white abs) have similar pressure ratings?

Retail on the A.O. smith pump was $650, but I bought it on eBay for less. Looks like a heavy duty motor, and is rated for pool use. I'll let my electrician decide what cable will be run between the VFD and the motor, but since it is a very small distance (12") I don't know that it really matters. Let me know if you think otherwise!

guamguy · Jul 25, 2011

I would check with A.O. Smith on whether or not the motor is rated for inverter duty. Speaking from first-hand experience, motors run on a VFD that aren't rated correctly will quickly fail, usually from overheating. The windings in a motor are cooled by the fan, which rotates at the same speed as the motor. When running at less than the design speed, there will be more heat buildup in the windings, which is why inverter-duty motors are built with more robust windings and cooling systems. Good luck with the project, I hope everything works out for you, it sounds interesting :goodjob:

mas985 · Jul 25, 2011

Schedule 40 defines only the dimensions of a pipe not the pressure rating so not all schedule 40 ABS will have the same pressure ratings. Schedule 40 ABS DWV piping found at many home stores have a maximum working pressure of 0 PSI listed as a specification. Foamcore pipe is much lighter than solid core but it is also weaker and does not hold up to pressure as well. Again, you might get away with it but given how difficult it is to replace buried pipe, I wouldn't risk it.

Does the standard product that one uses for pool plumbng (white abs) have similar pressure ratings?

Most pool plumbing uses PVC NOT ABS. If you insist on using ABS, just make sure it has a pressure rating stamp on the pipe itself and compare the specs to typical PVC specifications. Even though the steady state pressure of pool plumbing is fairly low, there are times where a pressure wave, hydraulic water hammer, can produce very high pressure that will stress the welds of the pipe, so it is important to get pipe that can survive over long periods of time. Also, make sure the fittings are pressured rated because sometimes those too have very low pressure ratings.

To add to what guamguy mentioned. An inverter duty motor will usually have a class F insulation rating. Plus most VFDs are not rated for outdoor use and will require a NEMA 3 or better enclosure. Also, make sure your electrician has experience installing VFDs and understands some of the issues with a VFD installation. Otherwise, you may be replacing your drive fairly quickly.