New Owner Build Plumbing Questions

[jte]

First post, my question is focused on plumbing, I wasn't sure if I should post here or in the "construction" forum. I can redirect if need be. I'll be starting my owner-build in ground 16x30 gunite pool shortly, permit is in process. I have all my subs lined up, and am comfortable I've found a good source of equipment, materials, and subs. I'm a commercial general contractor myself, so the construction part of this is no concern. My question is in regards to the engineered drawings I purchased. I hired the firm that everyone around west central Florida uses, he's been reliable and affordable. On his TDH calcs, he states the branch piping is to be 4" (between the drains), trunk piping to be 3" (from the main drain T and skimmer back to the pump), and return piping to be 2.5" He spec'd the Pentair Intelliflo VS 3hp pump and what seems to be correctly calculated TDH and pipe sizes based on water velocities. But the drain he's spec'd only has 2.5" sockets to tie the 4" branch piping together. I called him to question using such large pipes when all the filter, pump, skimmer, return eye, etc only provide for 2" maximum pipe size. He stated he's been made to comply with ANSI requirements for water velocities of 6 feet per second branch, 8 fps trunk, and 10 fps for return, and that per the chart, these are the required pipe diameters for a pump that can pull 140 gpm based on the TDH.

To put it simply, does any of this make sense? I'm not hiring a pool builder because the construction part of this is simple for me. I'm struggling with accepting this engineering at face value-seems odd to increase from 2.5" to 4" and reduce back to 3" back to the pump.

 

[Jimrahbe]

jte,

Welcome to TFP... A great resource for all your new build questions...

Not sure I can answer any of your questions, but I have never heard of 3" or 4" plumbing being used for a relatively small residential pool.

I know for a fact that all my plumbing is only 2" including all the main drain and skimmer plumbing. My pool is about the same size as yours will be, and I have the IntelliFlo.

We have some pretty sharp flow dynamics members here, so I will try to get one of them to chime in..

Thanks for posting,

Jim R.

 

[mas985]

What was the TDH that the PB calculated? In order for the Intelliflo to reach 140 GPM, the TDH would have to be below 60' of head which is nearly impossible for a residential pool. My guess is that he calculated it only for the pipe and maybe the fitting but nothing else. Can you get the calculations?

Or if you can get the schematic of the plumbing layout, I can calculate TDH.

 

[jte]

Thanks for the response, I've attached his calculations and I felt it was very simplistic. One thing that will keep the head pressure down is that the pump will only be 12-15' from the skimmer and a total of 40 linear feet from the main drains to the suction intake of the pump. Deep end main drains are 6'-6" deep. I plan on looping the return utilizing 4 return eyeballs, so that puts the total linear feet of return at about 110 linear feet from the pump, around the pool and connected back the loop T. My schematic was too large of a file to upload as is, if it'd be helpful to have more information I can reduce it in size and upload. ​

 

[PoolGate]

Does it really matter if you use 3" or 4" as apposed to 2"? Mine also is all 2" (29k gallons). I mean, what is the issue? Cost?

 

[jte]

Does it really matter if you use 3" or 4" as apposed to 2"? Mine also is all 2" (29k gallons). I mean, what is the issue? Cost?

Cost is not a consideration. It's an insignificant amount of material and most of my plumbing and electrical components are coming from work anyways. I'm not trying to reinvent the wheel, but when the PE's design is so much different than the norm, I question it. To my knowledge, residential pools use anywhere from 1.5" on the small end to 2.5" on the larger end. There has to be a point where plumbing that's too large has no effect or negative effect on functionality. I'm not building a water park. My concern is having a pipe size that is not only incompatible with the pool components (2" fittings on pump, filter, return eyes, main drain connections) and excessive use of reducers, and how that will impact the functionality of the water flow. I presume that at the relatively low speed the VS pump runs at for reasonable turnover, the velocity will be lower. Lower velocity means slower water movement around the pool and I believe that would impact filtration.

At the same time, I want to be sure what I put in meets all current requirements such as the pipe velocities shown in the calculation sheet attached above.

 

[mas985]

So that is a very simplistic method of calculating head loss and is usually always wrong. It assumes the flow rate is 140 GPM and then calculates the head loss of the plumbing. But only part of the plumbing. It ignores the head loss in the fittings, eyeballs, skimmers and main drains.

I will need the schematic if you want a more accurate estimate of the head loss. Note that you can upload the file on Google Drive or OneDrive or another cloud service and just post the link to the file.

 

[Jimrahbe]

jte,

Just for reference, I have 2" plumbing and run my Intelliflo at 1200 rpm most of the time. At that speed the filter pressure is only about 2 or 3 lbs.

Having to have X turnovers a day is an only wives tale and is just not necessary at all. My skimmers work fine at this speed. I used to increase the speed several times a day to "help" with skimming, but have found that it makes very little difference one way or the other.

Circulation and filtration removes the debris that get into a pool. Proper chemistry is what keeps your pool sanitized and sparkling clear.

Thanks,

Jim R.

 

[jte]

Linked is my layout, I really appreciate input on a more accurate TDH calc. I presume 4 return jets is sufficient, and I'm certainly open to suggestions on placement. Once again, my "trust but verify" approach is how I'll get this built. My sub that's doing all the rebar and plumbing has been in the business working for the major builders for 15 years, so he's got the experience. I'd just like to make sure he's not doing things the way they've always been done if there's a better way.
https://imgur.com/a/unnKl

 

[mas985]

The PB had a heater in his calculation. Do you have one?

 

[jte]

The PB had a heater in his calculation. Do you have one?

No, thank you for pointing that out. FWIW-this was an engineering firm, not a local pool builder. He didn't take much of my diagram into account when he calculated the TDH. I just needed his stamp for the structure.

 

[JamesW]

The engineer is calculating that the pump will be running full speed and just pulling from the main drain. That's not realistic. I would suggest a 2" line from each skimmer, a. 2.5" line from the main drains and (2) separate 2" returns.

Staying within the 6 ft/sec rule, you can get 90 gpm from the main drains and 63 gpm from each skimmer for a total of 216 maximum flow. That gives you 45 gpm at each main drain and 3 ft/sec in the branches going to the main drains.

Staying within the 8 ft/sec rule, you can get 84 gpm from each return for a total of 168 gpm.

Realistically, you wouldn't want to exceed those flow rates for individual suctions or returns anyway.

You can probably set a max rpm at the pump of about 2500 rpm and a normal filtration at about 1700 rpm or lower.

 

[mas985]

Here is the latest version of ANSI/NSF 50 standard that I can find: http://www.nsf.org/media/enews/documents/nsf_50_150715.pdf

Under 9.8.3 it states:

9.8.3 A skimmer’s maximum flow rating (GPM, LPM) shall be specified based on the nominal pipe size
intended to plumb the suction line (and/or equalizer line). The maximum velocity for any nominal pipe size
shall not exceed 6 FPS (1.83 MPS).

So the velocity requirement is for the skimmer as well.

Given the skimmer line is very short, that path will have the lowest head loss and highest velocity and be the limiting factor in this plumbing design. Reducing the size of the skimmer and MD lines would be a mistake because the head loss in this system is going to be very low and in fact even lower than what the PB estimated. Depending on the size of the eyeballs used, flow rates could easily exceed 140 GPM and maybe even reach run out which would be a disaster.

However, if you have 1/2" eyeballs, you can reduce the maximum flow rate to around 122 GPM at 79' of head which will meet the 6 ft/sec in the 3" suction pipe and 8 ft/sec in the 2.5" return pipe. 4" pipe would not be necessary in the MD TEE.

But do you know if this is actually required to pass inspection and how they would verify it anyway? That is not to say it isn't wise to design for this.

You may be able to argue that you will limit the pump's RPM such that it will never exceed the max velocity. The standard is a little vague on this point.

 

[JamesW]

Realistically, the pump should never run at full speed. It probably wouldn't need to exceed 60 gpm at any point.

 

[mas985]

I agree but i dont think that satisfies the standard. If the pump can be run at full speed, it must meet the standard at full speed. But i would check with the local building dept.

 

[jte]

Here is the latest version of ANSI/NSF 50 standard that I can find: http://www.nsf.org/media/enews/documents/nsf_50_150715.pdf

Under 9.8.3 it states:

So the velocity requirement is for the skimmer as well.

Given the skimmer line is very short, that path will have the lowest head loss and highest velocity and be the limiting factor in this plumbing design. Reducing the size of the skimmer and MD lines would be a mistake because the head loss in this system is going to be very low and in fact even lower than what the PB estimated. Depending on the size of the eyeballs used, flow rates could easily exceed 140 GPM and maybe even reach run out which would be a disaster.

However, if you have 1/2" eyeballs, you can reduce the maximum flow rate to around 122 GPM at 79' of head which will meet the 6 ft/sec in the 3" suction pipe and 8 ft/sec in the 2.5" return pipe. 4" pipe would not be necessary in the MD TEE.

But do you know if this is actually required to pass inspection and how they would verify it anyway? That is not to say it isn't wise to design for this.

You may be able to argue that you will limit the pump's RPM such that it will never exceed the max velocity. The standard is a little vague on this point.

Thats what I’ve been thinking. I clearly wasted my time asking for his TDH calcs. I did not submit these plumbing sizes in my permit due to my lack of confidence in these calcs. I do not know if inspectors in my area get detailed enough to even know about flow rates. My only goal is to install this for maximum efficiency and filtration effectiveness. With such a short run, would I be better suited with the 2hp Intelliflo VS and avoid the excessive flow capabilities of the 3hp? So, your suggestion is to use the 3hp pump and use 3” for skimmer and main drain runs and 2.5” for the return loop and 1/2” eyeballs? That’s what sounds right to me.

 

[JamesW]

You're never going to run the pump at full speed pulling from just one skimmer or just the main drains. It would violate the design flow rates of the skimmers anyway.

So, designing for it seems pointless.

I would find it hard to believe that any inspector would require 3" plumbing on a small residential pool.

As I noted above, 2.5" md and 2" skimmer lines provide plenty of flow and can handle the pump at high speed. Using 2 skimmers and the main drains allows for about 216 gpm.

 

[mknauss]

There is no 2 HP Intelliflo. The Intelliflo is a variable 'HP' pump. You only need to run it as fast as you need to.

If you are planning on automation, only the Intelliflo in the Pentair line communicates with the EasyTouch or Intellitouch.

Take care.

 

[JamesW]

The Intelliflo I1 and I2 pumps come with smaller impellers for areas that wouldn't allow the full power of the regular intelliflo.

However, that requires the pump to run at higher speed to achieve the same gpm. Higher speed is noisier than lower speed, so not a great choice.

The answer seems easy, just set the maximum speed to a reasonable level right away.

 

[mas985]

So, your suggestion is to use the 3hp pump and use 3” for skimmer and main drain runs and 2.5” for the return loop and 1/2” eyeballs? That’s what sounds right to me.

Yes, that would be my suggestion.

The answer seems easy, just set the maximum speed to a reasonable level right away.

If it were my family, I would not rely on just the limiting of the RPM. It is too easy to reset that. Plus, if the standard is enforced, they will enforce it at all possible scenarios including full speed.



The addition of smaller eyeballs would limit the flow rate even at full RPM so it meets the standard and is safe under all scenarios. Plus they do have a benefit as well. The higher exit velocity of smaller eyeballs allows the pump to have better circulation and surface action at lower speeds potentially reducing run time.