Spa/Pool Pipe Size Question after reading Hydraulics 101

[markmac]

I'm laying out a new pool/spa and am reviewing the plumbing layout. I reviewed the Hydraulics 101 and one point that I wasn't clear on was the following;

"On the return side of the pump, multiple lines can help reduce head loss as well but the equivalent size of all the return lines that run from pool to the pump should never exceed the equivalent size of all the suction lines that run from pool to pump or pump cavitation could become an issue."

Does this mean I need to ensure the total combined return GPM design of the pipe, is less than the total suction? I am planning a perimeter spa, and wanted to add a couple extra returns to push water/dirt around it, and then I also have planned one (maybe 3) Descent(s). I was originally plannign teh following, but if my understanding of the above is correct, I need to make my return's smaller?

Suction
Main Drain with a run of 40' using 3"
Skimmer#1 with a run of 15' using 2.5"
Skimmer#2 with a run of 70' using 2.5"

Return Side
Return #1 with a run of 70' using 2"
Return #2 with a run of 50' using 2" (for perimeter spa)
Return #3 with a run of 50' using 2" (for perimeter spa)
Return #4 with a run of 40' using 2"
Return #5 with a run of 35' using 2"
Return #6 with a run of 25' using 2"
Descent #1 with a run of 25' using 2"

Pentair VS 3HP Pump will only be 1'-2' above water line I suspect.

Using the table in the Hydraulics 101 for Flow rate of the various pipes, I show the following (GPM@6ft);

Suction = 2 [email protected]" + 1 Main @ 3" = 180+138 = 318 GPM @ 6ft
Return = 6 Returns @ 2" + 1 Descent @ 2" = 7 X 63 = 441 GPM @ 6ft
Even dropping the Descent, its still 378 GPM @ 6ft.

Do I have an issue? I can lower to 1.5", and run the Perimeter spa clean out returns off the same run, and that would balance it (assuming Descent run separate). Although I was also planning for a Spa Bypass return given the perimeter overflow.

Maybe I've missed a piece of the puzzle somewhere? Or am I over thinking this, because its not accounting for head in any of these calculations.

 

[ajw22]

@mas985 can fill in the details.

 

[mas985]

"On the return side of the pump, multiple lines can help reduce head loss as well but the equivalent size of all the return lines that run from pool to the pump should never exceed the equivalent size of all the suction lines that run from pool to pump or pump cavitation could become an issue."

Does this mean I need to ensure the total combined return GPM design of the pipe, is less than the total suction?

No. What that means is that you don't want the return head loss to be less than the suction side head loss. So in general, if all your plumbing is 2", then you want the number of return lines to be less than the number of suction lines. Having too many return lines can cause the return side head loss to be less than the suction side head loss. And by lines I mean separate pump to pool lines and not split/combined at the pool.

Suction
Main Drain with a run of 40' using 3"
Skimmer#1 with a run of 15' using 2.5"
Skimmer#2 with a run of 70' using 2.5"

Return Side
Return #1 with a run of 70' using 2"
Return #2 with a run of 50' using 2" (for perimeter spa)
Return #3 with a run of 50' using 2" (for perimeter spa)
Return #4 with a run of 40' using 2"
Return #5 with a run of 35' using 2"
Return #6 with a run of 25' using 2"
Descent #1 with a run of 25' using 2"

So the equivalent suction lines in 2" pipe would be a little over 5 which is pretty close to the 6 returns. But that is only if you are running all the lines at once. Were you planning to have all of these lines as separately runs pool to pump?

Suction = 2 [email protected]" + 1 Main @ 3" = 180+138 = 318 GPM @ 6ft
Return = 6 Returns @ 2" + 1 Descent @ 2" = 7 X 63 = 441 GPM @ 6ft
Even dropping the Descent, its still 378 GPM @ 6ft.

That would be the maximum flow rate you would want pass through the plumbing. Not the actual. The Intelliflo could never reach those flow rates.

Have you determined the flow rate you will need for an perimeter spill over? The Intelliflo XF might be a better choice.

 

[jimmythegreek]

How many sheers and what size? In typical basic plumbing, only for the pool, all the intakes for suction can be 2" home runs into a 2" manifold. The returns can be 1.5" and even 1.25" for homeruns of shorter lengths. 3/4" eyeballs put good backpreasure on those lines.
Now with sheers anything over 3ft is 2" plumbing and they need good water supply, often with their own suction point. On complex pools best bet is a separate pump and i would definitely do that in your case with a spa. Spas need water flow amd 2.5 and 3" lines are often necessary. The choke points are equipment with 1.5" fittings, nowadays 2" is more standard on middle/higher end equipment and they offer 2.5" taps as well on some stuff

 

[markmac]

No. What that means is that you don't want the return head loss to be less than the suction side head loss. So in general, if all your plumbing is 2", then you want the number of return lines to be less than the number of suction lines. Having too many return lines can cause the return side head loss to be less than the suction side head loss. And by lines I mean separate pump to pool lines and not split/combined at the pool.


So the equivalent suction lines in 2" pipe would be a little over 5 which is pretty close to the 6 returns. But that is only if you are running all the lines at once. Were you planning to have all of these lines as separately runs pool to pump?


That would be the maximum flow rate you would want pass through the plumbing. Not the actual. The Intelliflo could never reach those flow rates.

Have you determined the flow rate you will need for an perimeter spill over? The Intelliflo XF might be a better choice.

thanks for clarifying. I think I follow now, however it raised another idea and questions.

I think I can drop one run now. I have the trough drawn up to be only 6” wide and 6” deep. The spa will also be straddling the pool wall 50%, so the total trough is only 14’ (half the spa perimeter). As those two returns are for shallow, narrow water, I should be able to have one run, split at the spa, to the two return heads. When I run a skimming cycle, I would think any dirt/debris will flush out.

I’m planning to have every suction and return on its own line, except maybe now the two perimeter spa trough returns. So that would be 7 returns, on 6 runs, when I include the Spa bypass.

Reading various threads, I’m planning to run 3” both ways to the spa, and try and maximize jets.

Let me know if the following sounds like a problem, or where my logic falls down.

Pool and descent on one VS 3HP ( I’ll need to read up on XF). Pump would run through Filter, Heater and SWG. I likely would only run the descents when using the pool, so it’s likely pool OR descent for the most part.

Second VS pump dedicated to SPA, plumbed with 3” suction and return, and bypass both heater and filter. This way I max the return pressure so I can maximize jets. I believe the two negative tradeoff‘s are 1) the speed in which the Spa heats, as it would be limited to the single Pool Bypass return, with all pool returns closed and not cycling spa water, and 2) to use the spa, I’d have to mess with valves vs automation and all other returns would have separate runs and valves. Or is there a way to run dedicated SPA pump via heater until up to temp, and then switch to a Heater bypass Mode, while the pool is also plumbed to the heater?

As soon as I have the pool structure plans finished up, I plan to draft up the pad plumbing. Maybe it will jump out at me.

 

[markmac]

Have you determined the flow rate you will need for an perimeter spill over? The Intelliflo XF might be a better choice.

Crud. I hadn’t even considered the perimeter spill over rate!!! I assume it’s the surface area, multiplied by some vertical amount of water per second/min? Just trying to think it through, if it’s 7’x7’, and assuming 1” of water needed to spill over, that’s 4 cubic feet or 30 gallons! Even half that is still 15 gallons, but what period of time needs to be considered?

thanks for raising that, as I can see disappointment occurring if not considered.

 

[markmac]

How many sheers and what size? In typical basic plumbing, only for the pool, all the intakes for suction can be 2" home runs into a 2" manifold. The returns can be 1.5" and even 1.25" for homeruns of shorter lengths. 3/4" eyeballs put good backpreasure on those lines.
Now with sheers anything over 3ft is 2" plumbing and they need good water supply, often with their own suction point. On complex pools best bet is a separate pump and i would definitely do that in your case with a spa. Spas need water flow amd 2.5 and 3" lines are often necessary. The choke points are equipment with 1.5" fittings, nowadays 2" is more standard on middle/higher end equipment and they offer 2.5" taps as well on some stuff

right now it is planned at a single 36” descent. As I mention above, I’m thinking of running one VS 3HP for pool/descent, but only foresee running descents when using the pool. Otherwise leave it run a schedule of low flow swg and skimmer cycles. When running Descent alone, it would be pulling from 3” main drain.

with the pad being only 10’-15’ from the pool, I hope that also helps.

 

[mas985]

Crud. I hadn’t even considered the perimeter spill over rate!!! I assume it’s the surface area, multiplied by some vertical amount of water per second/min? Just trying to think it through, if it’s 7’x7’, and assuming 1” of water needed to spill over, that’s 4 cubic feet or 30 gallons! Even half that is still 15 gallons, but what period of time needs to be considered?

You can use the weir formulas. However for 1" you would need over 1000 GPM. For a 1/4", you would need 125 GPM. The rule of thumb is about 5 GPM per linear foot for a 1/4". Edges like that require a lot of flow rate ($$). You can go with less flow rate but then the edge height tolerance becomes tighter. To much variance results in an uneven flow over the edge with some dry spots.

Over the Edge - Water Shapes

Common to a huge percentage of watershapes, weirs play starring roles in the performance of everything from vanishing edges to naturalistic waterfalls. But common does not mean simple, says hydraulics expert Steve Gutai, who takes this opportunity to explore the physical characteristics of weir...

watershapes.com

 

[markmac]

Mark, thank you so much for asking the questions yesterday and the article. Reading that link was eye opening, disappointing, and also relieving to know I'm now informed and what to consider. Just doing an hour or two of further reading/research, and I think I'm turned off of the perimeter spa plan. Likely going to just look at a front spillway into the pool. That would cut the weir length to only 5.5' (7' exterior and assuming 9" walls????). In reading the various articles, seems like 1/4" or even 1/8" if leveled well can be assumed. Using the 1/4", and 5GPH per foot, I only need ~25 GPM.

Going this path would drop my two trough returns, so I'm down to 4 pool returns, plus the 1 spa bypass running at the lowest flow to balance turnover and power cost.

So with 2X2.5" Skimmers on separate runs, and a 3" main, should I be considering 2" or 1.5" returns, and then a 2.5" maybe for the spa Bypass?

 

[mas985]

I would stick with 2" return pipes and neck them down at the pool to standard 1.5" returns. Just put 2-way valves on every return pipe so if you have to make adjustments, you can. What is the spa bypass? Is that for the jets or for the spa heating or something else?

But for the spa, how many jets are you considering. That is also a problem area that needs some consideration. The flow rate per jet, & quantity figures into pipe size and pump size.

 

[markmac]

Thanks again. My plan is to have valves on every run so I can control every line. The spa bypass was my plan for keeping pool swg water cycling into the spa, and thus not need to switch pool/spa cycling times and overkill chlorine dose into spa. Originally it also maintain the spillover effect, but now realize I was blind to flow required.

For spa/Pool/Pump, I was planning the following to max spa pressure and # of jets.

Pool and descent on one VS 3HP ( I’ll need to read up on XF). Pump would run through Filter, Heater and SWG. I suspect I will only run the descents when using the pool, so it’s likely pool OR descent for the most part.

Second VS pump dedicated to SPA, plumbed with 3” suction and return, and bypass both heater and filter. This way I max the return pressure so I can maximize jets. I believe the two negative tradeoff‘s are 1) the speed in which the Spa heats, as it would be limited to the single Pool Bypass return, always with new pool heated water, vs cycled warmer spa water, and 2) to use the spa, I’d have to mess with valves vs automation given 4 pool returns.

Or is there a way to run dedicated SPA pump via heater until up to temp, and then switch to a Heater bypass Mode, while the pool is also plumbed to the heater?

 

[mas985]

Spa heating time is related to the heater size, not the flow rate.

Here are some of the ways that are used for pool/spa combos:

Jandy Valve Plumbing Schematics - INYOPools.com

Jandy Valve Plumbing Schematics - Learn how to plumb your swimming pool and spa

www.inyopools.com

This the one you would likely want to use:



Just make sure you don't have too many jets for the spa jet pump.

 

[JamesW]

I have the trough drawn up to be only 6” wide and 6” deep.

That's way too small. You need to go through the calculations again.

 

[markmac]

That's way too small. You need to go through the calculations again.

I'm now rethinking the overflow perimeter spa, but curious what dimension are you saying ti too small? If the through water level is the pool water level, I don't see how the spillover from the spa would cause any real increase in pool water level. Or are you referring to the width, and if the overflow would be projecting pas the 6" wide through? I'm only looking for the water to trickle down the sides, not pour out like descents.

 

[markmac]

Sorry, but James' question created a clarification for me.

Am I correct in that the 5GPH/foot @ 1/4" is to maintain a cohesive, 360 sheet effect of water coming off the spa "edge"?

I was only looking for an even trickle of water to run down the 12" spa exterior sides. "Assuming" gunite/tile can be within 1/4" or less across the 7x7, then am I okay with less flow?

 

[mas985]

Am I correct in that the 5GPH/foot @ 1/4" is to maintain a cohesive, 360 sheet effect of water coming off the spa "edge"?

5 GPM/ft. Not GPH/ft. More accurately, 4x7x4.5=126GPM

I was only looking for an even trickle of water to run down the 12" spa exterior sides. "Assuming" gunite/tile can be within 1/4" or less across the 7x7, then am I okay with less flow?

Yes but it may not flow evenly. The top would have to be almost perfectly level. So for 1/8" you need 44 GPM but the weir would have to be level to within 1/16" (half the water level) or there will be dry spots.

 

[JamesW]

I'm now rethinking the overflow perimeter spa, but curious what dimension are you saying ti too small? If the through water level is the pool water level, I don't see how the spillover from the spa would cause any real increase in pool water level. Or are you referring to the width, and if the overflow would be projecting pas the 6" wide through? I'm only looking for the water to trickle down the sides, not pour out like descents.

Maybe I'm not understanding the whole system?

It's complicated. I will look over it later. Just ignore my previous comments

 

[markmac]

5 GPM/ft. Not GPH/ft. More accurately, 4x7x4.5=126GPM

Yes but it may not flow evenly. The top would have to be almost perfectly level. So for 1/8" you need 44 GPM but the weir would have to be level to within 1/16" (half the water level) or there will be dry spots.

oops. Yes, per Minute.

126 GPM still seems like so much flow to just crest the water over the edge. In searching old threads I see discussions about 1HP pumps for pool infinity edge setups. For 126 GPM, I believe I'd need to be running the Pentair VS 3HP somewhere between 50%-75% continuously.

 

[mas985]

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In searching old threads I see discussions about 1HP pumps for pool infinity edge setups.

Can you post some links? Most setups require 3HP or larger but it does depend on the length of the edge.

 

[markmac]

the discussions I found pointed to this edition of waterscapes. https://watershapes.com/images/archives/2005/200508.pdf Page 63 talks about 160' of vanishing edge run on a 3/4HP pump. However they acknowledge that was not to be expected, and then believe their leveling was perfect.

Thanks for the plumbing design above. I think that could work, as the IntelliCenter turns on/off the Spa stand alone pump, and no valves to mess with. The auto-valve can then be on the pool pump, and just divert 100% to the spa bypass for heating.

This made me also think if it helps my perimeter flow rate? If I go as planend with two Pentair VS (or XF);

Pool Pump has 4 pool returns, and 2.5" spa bypass return.
Dedicated Spa pump running 3" suction/return.

Both pumps can be running much lower, and generate more GPM, at reduced power (I think?). The question is the sum of the two, achieving 125 GPM............back to school.