Spa/Pool Pipe Size Question after reading Hydraulics 101

[mas985]

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.

You would need extra valving since the jet only draws from the spa. If you want spillover, the jet pump would also need to draw from the pool. Also, you lose any of the benefit of running two pumps at lower RPM if any of the plumbing is shared between the two pumps. In other words, you need to keep the flow rate in all the pipes at half the GPM to get the efficiency.

 

[markmac]

Doh! Now I feel stupid. Just when I thought I had if figured out.

So if I plumb one skimmer with 3-way to have suction from the spa, or Pool; I have pool pump pulling from main drain and one skimmer, and Spa pump pulling from one Skimmer (2.5")? Then both are on independent suction lines from Pool, and both feeding Spa. Unless I'm missing another issue, which I probably am. Maybe the fact the Skimmer is 2.5" Suction and SPA return would be 3"?

 

[markmac]

Mark, When I draw out my idea in my last post, it seems to suggest it would all work, but I'd need dual, dual main drains in the Spa. Any rule of thumb for # of jets when a separate jet pump, bypassing heater and filter? Looking at the Pentair VS chart, and assuming minimal head loss on 3" pipe, over 75', I believe it suggests I can run each pump fairly low to produce 60(ish) GPM each.

Experiment Time
Last night I kept struggling with the 4.5gpm per linear foot of edge. I wanted to try and replicate it to see if it was to achieve a "sheeting" away from the wall effect, or just to evenly trickle over. I grabbed a 5 gallon bucket and measured three garden hoses separate to get their flow rates. I then shimmed the bucket level with a long bubble level, and a dime as a shim.

The bucket diameter was 1', so circumference 3.14 (aka π ). So using the 4.5 GPM rule, I would need ~14.13 GPM.

Hose #1 @ 2.4 GPM didn't produce an even spill over effect. probably 50-60% of edge spilled over.
Hose #2 @ 4.76 GPM produced a spill over (trickle) effect the entire circumference. No water was 'sheeting' away from the edge, just a steady overflow.
Hose #3 @ 6.52 GPM produced a spill over (trickle) effect the entire circumference. No water was 'sheeting' away from the edge, just a steady overflow. No noticeable difference from Hose #2, but yet 37% higher flow rate.

I then put all three hoses deep into the bucket to try and avoid/minimize circulation causing an effect.

Assuming each hose produced the same amount with all three running, as each did stand alone, they were collective pumping 13.68 GPM, still short of the required 14.13, but I was out of hoses.

With all three hoses, the full perimeter had a solid, and visibly even flow, as it did with Hose 2 and 3 in isolation. Just more water flowing over the edge. However, the most noticeable difference, was what appeared to be the water surface tension increasing, and raised above the lip of the bucket. It also seemed to cause the surface of the water to be "tighter" and more reflective.

I can only conclude that the difference between the total produced by all three hoses, and target (0.45 gpm), would allow the water to achieve the maximum height, or surface tension, above the ridge of the bucket.

Based on this, for a 7x7 overflow spa, I could run the pump at the minimum flow to achieve "spill over", but I'd need to approach 126 gpm to achieve the surface tension, and maximum water height. If my experiment is an indication, running at half the 126 gpm would still produce an even overflow (assuming reasonably leveled edge), just not the surface tension build up.

 

[mas985]

Again, it all depends on how even the installers can make the edge. It is not easy to make a 30' long edge that even. The 126 GPM was based upon a 1/4" water height and a 1/8" tolerance on the edge. A bucket is actually nearly perfect edge so not a very good proxy for the tile edge.

As for the jets, it really depends on the type of jet used. They range from 10 GPM to 25 GPM per jet. What you get out of the pump depends on the complete design of the plumbing.

 

[jimmythegreek]

It takes high quality labor to make a dead even edge and good material substrate too.

 

[markmac]

Is it common to see these overflow spas not leveled precise enough? I've never saw one in person, but every PB around is flashing pictures of their overflow spa builds.

Looking closely, they all slope the top edge of the spa inward, I assume to make just the exterior wall edge the top, and less surface area to level.

I have an engineering background and done precise leveling many times; many, many years ago. Measuring level I can check to 1mm, but I guess the point you're driving home is the tile work and substrate needs to be "top shelf".

 

[ajw22]

You expect the PBs to show you pictures of their problem childs?

We get the pictures posted here of the uneven spillovers and walls. There was a recent thread of a spa spiilover that was a full wall and one side settled just a hair so the water flow is now uneven.

 

[markmac]

true enough! I guess writing it into a contract is the only protection. Overflow edge must be within 1/8" absolute level. Ideally a second level assessment before payment for some of these massive infinity edge pools.

I assume its like any other construction, where the prep work is key? I assume you need the gunite crew to get as close to level as possible, to allow the tile crew to start from the best position they can. Then its up to the tile crew being on their game? How does a tile crew (who knows their stuff) prep the edge? Do they set a laser level inside the spa?

 

[ajw22]

Contracts and specification don't protect you from sloppy work. They are good references for the lawyers and judges during the dispute resolutions.

You think the workers shooting the gunite or laying the tile has seen the contract specification?

If you want tight tolerances then you have to personally be on top of the crews, or hire someone as your agent, who is reviewing the work as it is done and telling them what is acceptable or not.

Read this thread about the sloppy work that was finally fixed as the owner and his hired expert supervised the work...

Fiberglass Pool Install

The equipment installation guide said to use a 90 degree radius pipe. What do the members think/feel about this?

www.troublefreepool.com

 

[mas985]

true enough! I guess writing it into a contract is the only protection. Overflow edge must be within 1/8" absolute level. Ideally a second level assessment before payment for some of these massive infinity edge pools.

Don't forget that tolerance has to be half the water height. So if you are targeting 1/8" water height, the tolerance must be 1/16" not 1/8".

 

[markmac]

while I know 1/8“ level can easily be measured, I’m not familiar with tile work to appreciate how hard it is to set that precise. A lot of the pictures I see of new spillovers, they use 1” tiles and I would assume it’s even harder to hit the level required.

 

[markmac]

I'm looking at the Intelliflo XF, and trying to determine if its advantageous to use two pumps on the spa, vs one, for the overflow requirement of ~125-130 GPM.

When considering the Spa XF, with a valve for overflow OR Jets, with 45' of 3" pipe (suction/Return), only 2 or 3 angles, and a pool skimmer suction with 3", the head loss is pretty minimal. Suction on 3" pool skimmer, and 3" overflow return to Spa. If I'm reading the curve correctly, maybe 2,000 RPM?

If I look at having the Pool XF also plumbed for a 3" line to the SPA for overflow/heating, it would only be the added head loss of the filter (520) and heater, plus main drain/second skimmer head loss.

So if I were to be running both XF at lower RPM, so each generates 65 GPM to the spa on separate 3" runs, the RPM's should be half or less than the single SPA XF running 130 GPM.

I'm not sure how to balance the equation to see the value of running the 3" Pool XF pipe, over a 2" for heat only, and additionally a 3" skimmer run for SPA pool suction to supplement the SPA overflow. Pipe is cheap enough over these short runs I guess.

 

[mas985]

When considering the Spa XF, with a valve for overflow OR Jets, with 45' of 3" pipe (suction/Return), only 2 or 3 angles, and a pool skimmer suction with 3", the head loss is pretty minimal. Suction on 3" pool skimmer, and 3" overflow return to Spa. If I'm reading the curve correctly, maybe 2,000 RPM?

There is also head loss in the spa jets, heater, filter, etc. These components will probably end up being much higher than the plumbing.

But I am not entirely sure what you have in mind with regards to two pumps. If you can draw out the schematics for the two proposals, I can help with the head loss/energy use calculations.

Also, have you picked out the spa jets yet? Different designs have different GPM requirements and so will affect the design.

 

[markmac]

Attached is what I'm working up in CAD. I'm trying to illustrate all the plumbing in CAD so I can start getting quotes.

The Spa pump won't run through the heater, or filter. I also plan to have a diverted valve so the pump either pushes a straight 3" overflow line to the spa, or the jets. one or the other. So in overflow mode, the pump woudl not feed the jets. Just pull from pool skimmer (3"), and return to Spa overflow 3". The 3" skimmer suction would only be 15' from pump, and then 3" return 45'. With little to no vertical elevation change from suction to return ends (raised spa), I have to believe the head loss will be negligible.

The other pump is the pool regular pump, and I'd just have a 3" return to the spa that I could also isolate and just push into the spa. This pump will also have a drain to spa, so I can circulate water from spa, to filter, heater, and then return.

My logic is two pumps working at very low RPM has to be much more efficient than one pushing twice as much GPM.

Have not looked at jets yet. That's next, but have been reading the various threads and articles suggesting pick the jet, then design the rest. In general, looking at jets having their own 3" return, then split into 6 jets, with Venturi 15'-20' away.

 

[mas985]

The other pump is the pool regular pump, and I'd just have a 3" return to the spa that I could also isolate and just push into the spa. This pump will also have a drain to spa, so I can circulate water from spa, to filter, heater, and then return.

So for the overflow mode, would this second pump draw and return to/from the same 3" lines as the other pump. What lines are in common, and what lines are duplicated? It makes a huge difference because the flow rate in those lines would be double or have a 4x difference in head loss. If the two pumps share all plumbing, then they might use more energy than a single pump. If the plumbing is completely separate, the energy use is much less than the single pump.

 

[markmac]

All separate. In spa over flow mode, it would be;

pump 1 - suction main drain and one skimmer. All separate 3”. Return one stand alone 3” to the spa.
pump 2 - suction second skimmer on 3”. Return one stand alone 3” to spa.

with Diverted shutting off jets, spa would have two separate IntelliFloXF, each with separate 3” lines feeding it.
pump 2 would have no other plumbing to pass through. Pump one would pass through filter and heater.

 

[mas985]

So assuming I got everything correct:

Scenario #1 Single Pump

RPM 2550
GPM 130
Head 27'
Watts 1500

Scenario #2 Dual Pumps - Optimized for energy (i.e. Same RPM but not same GPM, total = 130 GPM)

Pump #1 - Filter + Heater

RPM 1480
GPM 55
Head 14'
Watts 294

Pump #2 - No extras

RPM 1480
GPM 75
Head 9'
Watts 334

I assumed the pad plumbing for pump #1 would be 2.5" instead of 3". So the total for the two pumps would be 628 watts vs 1500 watts so over to 2:1. However, there is an economical consideration. Will the extra cost of the pump pay for itself over the life of the pump. It depends on the run time. It doesn't "need" to run all the time.

 

[markmac]

Thank you. This is exactly what I was trying to solve. I assumed it would be better, but I’m surprised it’s 2:1. With electricity here being only $0.15/kW, I don’t foresee paying for the pump, as that would take about 4 years running 6h a day which it wouldn’t. However, it’s not the pump to offset here, as I was planning for two pumps to run pool, and Spa. Therefore the cost is actually the extra 3” runs to offset.

Now to work out the jet plumbing. After reading the waterscape article, I think I’m on my way, with 3”, to 2” manifold, to 1.5 jets x 6.

Given the IntelliFlo XF and my plan, I should have plenty of GPM, but I believe its now velocity I need to focus on, and which jets.

 

[markmac]

While I was planning to plumb 3" lines from the pool main drains, any reason to drop them and just add side drains higher? Or is it feasible that just plumbing the skimmers with 3" lines provides the same flow I would need? And maybe a deep water return for circulation?

I've been reading various comments about how main drains are just legacy and more problems than their worth. I'm happy to drop them but not sure what I'm giving up in suction capacity I'd need for the IntelliFlo XF.

 

[mas985]

Deep water circulation is better handled with returns rather than suction ports. In order to get maximum skimming at the lowest flow rates, you are better off with just skimmers.