Plumbing Pipes

[Av8te]

I am trying to figure out the suction side and return pipe sizes of my system. Total gallons in pool is 52k, I have two skimmers, a main drain, and a spa drain to provide return water to 2
Returns in the spa and 8 in the pool. I am considering the Tristar VS 950 pump and calculated with 2.5 inch pipe for suction and 2.5 for returns I would be at 86tdh which doesn’t seem to work. I would only get about 80gpm at that tdh. This would take over 10 hours to turn the pool once. Do I need to go up to 3 inch pipe? 3 inch suction with 2.5 inch returns would give me about 64tdh and 135 gpm at 3450 rpm. That also puts me near the max of 138 for 6ft/ sec. any help is appreciated. This is an owner build if it isn’t totally obvious. Just trying to make sure I size things properly. I was planning these numbers on 2.5 inch for the returns. If I did 2 inch returns I would have 72tdh and about 110 gpm. Is that sufficient? If I should look at a different pump for this I am not stuck on that particular one. Just want to stick with Hayward.

 

[Texas Splash]

Welcome to TFP! To help you with this question, I'm going to tag @mas985. In the meantime, have the following info available:
- Update your signature (see mine as an example)
- Distance from equipment pad to pool
- Any elevation changes?
- Any other water requirements/features? (solar, fountains, etc)

We'll od what we can to help.

 

[HermanTX]

This is some notes I have kept from previous posts on the forum. Others with more experience on plumbing may have additional info.

PVC length – between pool/spa and equipment pad

For suction, you want to keep the water velocity below 6 ft/sec. For returns, you want to keep the water velocity below 8 ft/sec.

Size.......6 ft/sec......8 ft/sec.
1.5"...........38...............51 gpm
2"..............63...............84 gpm
2.5............90.............119 gpm
3.0".........138.............184 gpm

As long as the length is less than 100 feet and you follow the above rules, the system should be fine.

Over 100 feet, go up one pipe size.

To be conservative, you can use 6 feet per second for the return instead of 8 feet per second.

For returns close to 100 feet, suggest the following maximum flow rates.

Size.......Suction......Return
1.5"...........38...............45 gpm
2"..............63...............75 gpm
2.5............90.............105 gpm
3.0".........138.............160 gpm

 

[Av8te]

This is some notes I have kept from previous posts on the forum. Others with more experience on plumbing may have additional info.

PVC length – between pool/spa and equipment pad

For suction, you want to keep the water velocity below 6 ft/sec. For returns, you want to keep the water velocity below 8 ft/sec.

Size.......6 ft/sec......8 ft/sec.
1.5"...........38...............51 gpm
2"..............63...............84 gpm
2.5............90.............119 gpm
3.0".........138.............184 gpm

As long as the length is less than 100 feet and you follow the above rules, the system should be fine.

Over 100 feet, go up one pipe size.

To be conservative, you can use 6 feet per second for the return instead of 8 feet per second.

For returns close to 100 feet, suggest the following maximum flow rates.

Size.......Suction......Return
1.5"...........38...............45 gpm
2"..............63...............75 gpm
2.5............90.............105 gpm
3.0".........138.............160 gpm

The length from the pool house to the closest corner of the pool is about 60 feet. The pool length is 60 so to the farthest end of the pool would be about 120 feet. Also the area is fairly level so maybe only 1 or 2 feet higher to the pool house.

 

[mas985]

calculated with 2.5 inch pipe for suction and 2.5 for returns I would be at 86tdh which doesn’t seem to work.

Exactly how did you calculate that? TDH calculations are non-trivial and require detailed knowledge of every part of the plumbing system including eyeballs, skimmers, heaters, filters, valves, etc. TDH is also dependent on flow rate so you need to solve for the operating point which is the crossover between the plumbing curve and the pump's head curve.

Also, turnover is not really a requirement for a pool.

But I would not really worry too much about it. The Tristar VS 950 pump will work for most any pool and 2.5" plumbing is more than sufficient. Note too, you really want to operate at the lowest flow rates possible and not at the highest flow rates. So water velocity is not really all that relevant for normal operation. It would be if you had a high flow rate application.

 

[Av8te]

Exactly how did you calculate that? TDH calculations are non-trivial and require detailed knowledge of every part of the plumbing system including eyeballs, skimmers, heaters, filters, valves, etc. TDH is also dependent on flow rate so you need to solve for the operating point which is the crossover between the plumbing curve and the pump's head curve.

Also, turnover is not really a requirement for a pool.

But I would not really worry too much about it. The Tristar VS 950 pump will work for most any pool and 2.5" plumbing is more than sufficient. Note too, you really want to operate at the lowest flow rates possible and not at the highest flow rates. So water velocity is not really all that relevant for normal operation. It would be if you had a high flow rate application.

I calculated it based on length and most the fittings required such as the 45s and T’s?and valves. I did not calculate it based on the heater or swg or any of those components cause I don’t know which ones specifically I am using yet. I am trying to get the rough in plumbing done. Are you saying 2.5 will work for both the suction side and return side?

 

[mas985]

Yes, 2.5" is more than sufficient for that pump. Unless you have a very high flow water feature.

Also, I suspect you are not calculating the head loss correctly. Head loss is related to pipe length but does not equal pipe length so you cannot just sum up the length of pipe. Assuming 60' runs and a typical plumbing setup with a cartridge filter and NG heater, the operating point at full speed with that pump would be about 113 GPM @ 74' of head. But again, there should be no reason to run at that speed unless you have a high flow water feature. Dropping the RPM down to a more reasonable 1000 RPM would drop the flow rate down to 33 GPM @ 6' of head loss which is fine for skimming and general circulation.

 

[Av8te]

Yes, 2.5" is more than sufficient for that pump. Unless you have a very high flow water feature.

Also, I suspect you are not calculating the head loss correctly. Head loss is related to pipe length but does not equal pipe length so you cannot just sum up the length of pipe. Assuming 60' runs and a typical plumbing setup with a cartridge filter and NG heater, the operating point at full speed with that pump would be about 113 GPM @ 74' of head. But again, there should be no reason to run at that speed unless you have a high flow water feature. Dropping the RPM down to a more reasonable 1000 RPM would drop the flow rate down to 33 GPM @ 6' of head loss which is fine for skimming and general circulation.

For the suction side of things I had roughly 600 feet of pipe total between all the skimmers and drains etc. I included rise from 10 feet deep as well as added artificial length that 45s and T’s add
To the system to get at my tdh number. I used the table found here https://media.wattswater.com/Orion-HP-FrictionLoss.pdf. To get the total tdh I did the same with the returns. I used the tables here PVC Pipes - Friction Loss and Flow Velocities Schedule 40
To get the multiplier for the tdh. I have no idea what I am doing so I am sure I did some of this wrong so any guidance is much appreciated. Also all my water features will be on a separate pump that I haven’t sized yet and my spa will have another pump dedicated for that.

 

[mas985]

600' seems very high for the suction side equivalent length. Do you have a break down of the lengths/fittings and configuration (e.g. suction side home runs)? Also, did you take into account parallel pipes vs series pipe? Parallel pipe reduces the effective total length of the pipe. If you have a MD and 2 skimmers, that is 3 parallel lengths which reduces head loss by a factor of ~1/9 because flow rate is split between the 3 lines. If you want the head loss with only one of the lines, then you don't want to include the other lines in the calculation.

 

[Av8te]

600' seems very high for the suction side equivalent length. Do you have a break down of the lengths/fittings and configuration (e.g. suction side home runs)? Also, did you take into account parallel pipes vs series pipe? Parallel pipe reduces the effective total length of the pipe. If you have a MD and 2 skimmers, that is 3 parallel lengths which reduces head loss by a factor of ~1/9 because flow rate is split between the 3 lines. If you want the head loss with only one of the lines, then you don't want to include the other lines in the calculation.

I think the farthest is the main drain at 145 total feet not including added feet for 45s and t’s. The skimmers are closer than that and the spa drain is only 85 feet. I am planning on having the main drain and skimmers set to difference percent of total suction as was suggested on another thread. Maybe 25 percent on the md and keep the skimmers full open.
Does it seem like I could get away with 2inch with This system or would you run 2.5?

 

[Av8te]

Yes, 2.5" is more than sufficient for that pump. Unless you have a very high flow water feature.

Also, I suspect you are not calculating the head loss correctly. Head loss is related to pipe length but does not equal pipe length so you cannot just sum up the length of pipe. Assuming 60' runs and a typical plumbing setup with a cartridge filter and NG heater, the operating point at full speed with that pump would be about 113 GPM @ 74' of head. But again, there should be no reason to run at that speed unless you have a high flow water feature. Dropping the RPM down to a more reasonable 1000 RPM would drop the flow rate down to 33 GPM @ 6' of head loss which is fine for skimming and general circulation.

Does it matter that at 33gpm it will take almost 27 hours to fully turn the water in the pool?

 

[mas985]

I would draw only very small amounts from the MD. They are pretty useless. That way you can reduce RPM as much as possible for the maximum amount of energy savings. Currently I have my MD at less that 1% draw with the skimmers fully open.

Does it seem like I could get away with 2inch with This system or would you run 2.5?

The difference is not that much. However, I would go with the larger pipe at least on the suction side. It helps prevent clogs and at some point, you may want to run with just one suction line so it is always a good idea to upsize the suction line. Changing from the 2.5" to the 2" on the return side is only worth a couple of feet of head at full speed. Less than 0.3' of head at 1000 RPM (~10% GPM loss).

Does it matter that at 33gpm it will take almost 27 hours to fully turn the water in the pool?

No, as I mentioned before, turnover is irrelevant. It has no bearing on water quality. Many people on this forum including myself run at << 1 turnover per day.

Determine Pump Run Time

To figure out how many hours you need to run your pump, you need to know how fast your pump works. You can find this here.

www.troublefreepool.com

https://www.troublefreepool.com/threads/pump-run-time-and-turnover.41357/

There is also a pump run time study in my signature that proves it.

 

[ferretbone]

Does it matter that at 33gpm it will take almost 27 hours to fully turn the water in the pool?

Turn over rates in TX are 6 hrs for pools, 30min for spas, water parks and specialty pools is 1-4 hrs. So yeah turn over rates are in play here. Flow rate = pool volume (divided by) turnover rate (divided by) 60min. Download or buy a pool and spa operater book if your going to gets into this much detail. You will need a flow meter, or a return pressure gauge, to know for sure, so if you dont have one or both guessing is a waste of time.
Bottom line 2inch or 2.5 inch pipe is more than enough. Dont worry about T's, 90's, filters, or heaters. The Tristar is more than enough for your pool and spa. . Your filter if sized correctly and heater are all mathematiclly modeled and designed for over 8hrs turn over. All of this is in a CPO handbook. Just run your pump at 2400 3400 RPMs for at least 4hrs in the summer, or longer. In TX we have to run at least 8hrs during the day.

 

[mas985]

Those rules are only for commercial pools not residential. There is a huge difference in terms of bather load.

 

[ferretbone]

Those rules are only for commercial pools not residential. There is a huge difference in terms of bather load.

"Those rules are only for commercial pools not residential".

No not really. Those "rules" are code for commercial pools, but they are the industry standard for the South. Nothing I said leaves residential exempt, thoses standards apply to residential too. From the manufacturers, pool builders, and down the list. Residential properties just do not have code compliance from the city or State enforcing them. They do however enforce the manufacturers, pool builders and down the list. I have plenty of advice and tips that wouldn't even meet what you called the rules for reidential pools, but the OP clearly wanted to get closer to some kind of excepted standard so I started with the very minimum "rules" (the industry standard). You are right though, he can and should do whatever he wants.

 

[JamesW]

A typical-use pool should have a pump and filtration system capable of pumping the entire contents of the pool though the filters every 6 hours.

Chapter 14: Residential Swimming Pools and Spas | Healthy Housing Reference Manual | NCEH

NCEH provides leadership to promote health and quality of life by preventing or controlling those diseases, birth defects, or disabilities resulting from interaction between people and the environment. Site has information/education resources on a broad range of topics, including asthma, birth...

www.cdc.gov

The system should be designed to be "capable" of doing a 6 hour turnover, but there is no expectation that it should turnover that often.

Different sources will have different recommendations or suggestions about how much turnover is needed or optimal.

A lot depends on how much use the pool gets.

For residential pools, the flow should serve a specific purpose.

If someone has a variable speed pump, they can find the optimal amount of circulation for their particular circumstances.

If someone has a single speed pump, designing for a 6 hour turnover will usually be a design with a pump that is excessively oversized and wasteful.

Only under very high use situations will turnover in 6, 12 or 24 hours be helpful.

In most cases, the circulation only needs to provide enough flow for things like skimming or allowing the SWG or heater to work.

 

[JamesW]

For the suction side of things I had roughly 600 feet of pipe total between all the skimmers and drains etc. I included rise from 10 feet deep as well as added artificial length that 45s and T’s add.

It does not work like that.

When pulling from the main drain, you do not use the depth of the main drain.

The main drain can be 100 feet deep and it makes no difference from a static head point of view.

You only add static head from the surface of the pool water to the pump inlet.

Each skimmer and main drain should not be expected to provide more than 60 gpm.

At 60 gpm each, you can get to 180 gpm.

At 60 gpm through 2" PVC pipe, the velocity is 5.9 feet per second and the head loss is 5.8 feet per 100 feet of pipe.

If we assume a total equivalent length of 150 feet, the head loss is 8.7 feet.

That is the total head loss for 180 gpm going through (3) 2" pipes at 150 feet total equivalent length each.

You do not add up the head loss and you do not add up the total length of the pipe.

The total head loss of multiple similar pipes is the head loss of a single pipe.

Even if you had (100) 100 foot long 2" suction lines providing 60 gpm each (6,000 gpm), the total head loss is only 5.8 feet.

The power needed at the pump will go up as the flow increases, but the head loss does not.

The power required for 100 times the flow at the same head loss by adding more pipes will be 100 times more power.

A 6 hour turnover is 144 gpm for a 52,000 gallon pool.

Assuming a well designed system you have the capability get to 144 gpm.

However, as noted, there is no reason to try to get to this number.

In most cases, the best way to operate a variable speed pump is to run as slow as possible while providing enough skimming action and enough flow for the SWG to work.

If you will have a gas heater, heat pump or solar, you want automation that will increase the pump speed to the required flow for the heat source and then reduce the flow rate back down after the call for heat has been satisfied.

Typically, you need a minimum of 10 gpm per 100,000 btu/hr. For example, a 400,000 btu/hr heater requires a minimum of 40 gpm.

There would really never be a need to go above 40 gpm in most cases for most residential pools.

The actual amount of turnover should be based on providing enough skimming, enough time for the SWG to produce enough chlorine and enough filtration to maintain good clarity.

There is really no point to targeting an arbitrary turnover time.

In most cases, 15 to 20 gpm for 24 hours will give good clarity and good water quality and it will be the most efficient.

15 gpm for 24 hours is 21,600 gallons per day.

18 gpm for 24 hours is 26,000 gallons per day, which is 0.5 turnovers per day for a 52,000 gallons pool.

20 gpm for 24 hours is 28,800 gallons per day.

You should get a big cartridge filter (400 to 500 square feet) as it is the most efficient.

I have two skimmers, a main drain, and a spa drain to provide return water to 2
Returns in the spa and 8 in the pool.

If you will have spa jets, that usually requires a lot of flow.

For example, 8 jets that require 12 gpm each is 96 gpm.

In a case like that, the suction should be sized accordingly.

For 96 gpm, the spa suction should be 3"

 

[JamesW]

If you have 2 independent 2” PVC returns at a total flow of 150 gpm, the velocity is about 7.3 feet per second and the head loss is about 8.8 feet per 100 feet of pipe.

At a total equivalent length of 150 feet, the total head loss is 13.2 feet.

The total dynamic head loss from the suction and return plumbing is 13.2 + 8.7 = 21.9 feet.

The static head loss cancels out and it can be ignored.

Every component in the system creates head loss, which should be available from the manufacturer.

For example, the graph below shows the filter head loss vs. the flow rate.

At 144 gpm, the head loss is about 15 feet.

https://www.hayward-pool.com/assets/documents/pools/pdf/manuals/SwimClear-Cxx30-revB.pdf

The total dynamic head loss from the suction and return plumbing plus the filter at 144 gpm is 13.2 + 8.7 + 15 = 36.9 feet.

If you look at the pump performance curve, you can see that at 3,000 rpm, you can get to about 144 gpm at about 34 feet of head.

At 3,450 rpm, you can get to about 144 gpm at about 57 feet of head.

As long as the other components of the system don’t add more than (57 - 36.9 = 20.1) feet of head at 144 gpm, you can get to 144 gpm if you wanted to.

In any case, you should never need more than about 40 gpm maximum, so it’s really mostly a moot point.

 

[JamesW]

Edit.

The head loss at 144 gpm for (3) 2” PVC pipes is based on 48 gpm per pipe, which is about 4.68 feet per second and the head loss for 150 feet of pipe (total equivalent length) is about 6.67 feet.

For (2) 150 foot 2” returns, the flow is 72 gpm, the velocity is 7.02 feet per second and the head loss is about 14.13 feet.

The total head loss from the suction and returns would be about 20.8 feet.

Hazen-Williams Friction Loss Equation - calculating Head Loss in Water Pipes

Friction head loss (<i>ft_H2O per 100 ft pipe</i>) in water pipes can be estimated with the empirical Hazen-Williams equation.

www.engineeringtoolbox.com

 

[JamesW]

I would probably target about 18 gpm continuously for 24 hours per day.

The cost to run at 18 gpm for a well designed system should be very low and you can check the actual power usage from the pump control panel to verify.

I would do about 8 gpm per skimmer and about 2 gpm from the main drain.

For a heater application, have the automation increase the pump to the required flow for the duration of the call for heat and then resume the 18 gpm flow rate.

Adjust the SWG output as needed.

If you will have any high flow requirements, please specify them for consideration.

Things like big slides, fountains, sheer descents etc. all take a lot of water and need to be taken into account for system requirements.

If you will have an infinity edge, that will usually require an extra separate high flow pump.