Standards on properly sizing a Surge/Balancing tank for a perimeter overflow pool?

[DougS78]

We have a perimeter overflow pool that was finalized at the tail end of last pool season, thus we have had limited time to use it. The pool is designed with a 360 degree perimeter overflow. As such the water is designed to flow over a ledge into a trough under the pool deck around the pool.

In the limited time last year, the overflow feature did not function as it had been advertised as the pump would not draw and reservoir would drain out during operation. This would appear to be due to an insufficient sizing of the reservoir (surge tank or balancing tank) that supplies the overflow feature. Nonetheless the pool builder contends it is sized correctly.

I am wondering if anyone can point me to any sort of authoritative source regarding the calculations for sizing this tank?

 

[AQUA~HOLICS]

Are you saying that the catch basin is overflowing or running out of water during operation?

 

[DougS78]

Are you saying that the catch basin is overflowing or running out of water during operation?

Are you saying that the catch basin is overflowing or running out of water during operation?

Yes, that is correct. There are several issues, but when the pool company first started it, it took quite a lot of time and effort to get the pump to prime. They did so by running a hose directly into the reservoir for some time and kept the hose running while the overflow pump ran. So much so that when it was turned off, several hundred gallons of water flowed out of the reservoir into our yard.

This is supposed to be controlled from our phone (Hayward) and I could never get the pump to run this way. At one point it was running, but it would make a sucking sound as the water in the tank got below the exit pipe. It kept running but obviously the flow was restricted.

It was sold as a "feature" that we could turn on and off. In fact, they said that it would not be advisable to run this during swimming as it would cause water to overflow onto the pool deck as the slot is only 1" and can't handle bathing surge. Needless to say, it doesn't function this way.

 

[DougS78]

I'll add that I'm happy to supply any other details that would be helpful and would welcome any input on this from folks here. But even if someone could point me to a resource that specifies how these decisions should be made, it would be helpful. Most things I can find suggest rules of thumb such as "5-10% of pool volume." Ours is well short of this at ~2% of pool volume. Another local pool provider I consulted with said they would have put in something even larger -- up to 20% of pool volume (5K gallons) in order to be sure it always had supply and capacity.

The pool builder did provide a set of technical calculations for the hydraulics (i.e. rate of flow over weir, etc), but this doesn't take into account the amount of water in the pipes going from reservoir to pump, pump to pool, and pool trough back to reservoir. Not to mention functional considerations such as water displacement from bather load as well as evaporation. When I inquired about this, they just stonewalled and said the reservoir was sized correctly.

 

[ajw22]

I am wondering if anyone can point me to any sort of authoritative source regarding the calculations for sizing this tank?

There are none. There are ANSI Standards for public pools for safety...

Purchase or Read PHTA Standards

Codes, standards, and regulations vary between jurisdictions, which can make them complicated to navigate, but compliance is critical. Understanding and applying the rules and regulations which govern industry activities prov

www.phta.org

2018 INTERNATIONAL SWIMMING POOL AND SPA CODE (ISPSC) | ICC DIGITAL CODES

ICC Digital Codes is the largest provider of model codes, custom codes and standards used worldwide to construct safe, sustainable, affordable and resilient structures.

codes.iccsafe.org

Was there an engineer involved in the design of your pool? Did you have an engineers stamp on the pool blueprints and design documents? I would go back to him with your design problems.

What was your builders prior experience in building perimeter overflow pools?

I offer you the reading materials below. The design that you describe with a 1" slot and a manually controlled pump is not the design that I have read about.

https://www.poolspanews.com/how-to/design-construction/beauty-of-the-edge_o

https://www.poolspanews.com/how-to/design-construction/evolution-at-the-perimeter_o

A Pocket Guide to Building Vanishing Edge Pools

Advice for avoiding costly errors in vanishing-edge projects.

www.aquamagazine.com

Building a "Perimeter" overflow type pool

Hi to all at TFP! I am presently building a pool from the basement upwards(the pool surface is at ground floor, pool structure below an excavated basement) in the centre of a "Courtyard House" , (also under construction),so that the overflow edge is leveled with the courtyard flooring at Ground...

www.troublefreepool.com

 

[JoyfulNoise]

This may not be the “correct method” for calculating this but it gives you the idea of the scale involved. Let’s assume your overflow would need to handle 1/4” of water coming off your surface area of the pool -

20’ X 40’ X (0.25” / 12) = 450 cu ft ≈ 1870 gal

Now let’s assume that your perimeter overflow is such that a 3/8” square of water falls over the edge of the pool -

(40 + 40 + 20 + 20) X (3/8”)^^2 ≈ 126 gal

For a 1/4” square that goes down to 56 gallons

So just doing some very rough bar napkin calculations, I would surmise that your basin needs to hold roughly 2000 gallons of water to be safe AND you would need a MASSIVE sump pump to achieve enough flow rate to move a 3/8” column of water over the entire perimeter edge of a pool that size. Most pool pumps can’t do more than 120GPM of flow rate without some seriously large diameter pipes.

I think your tank and pump are likely undersized for the task.

 

[ajw22]

These articles about Infinity Edge pools may help you…

https://oceanquestpools.com/wp-content/uploads/2022/04/CONTAINMENT-WITH-VANISHING-EDGE-2003.pdf#:~:text=There%20must%20be%20enough%20water%20to%20flood%20the,to%20capture%20splash-out%20and%20water%20lost%20in%20winds.

Vanishing Edges 101

Avoiding the Pitfalls of Vanishing-Edge Pool Construction

@setsailsoon is currently designing a pool with an overflow edge and may be helpful.

 

[AQUA~HOLICS]

Janine Wilson from Pool Zones may be the contact you’re looking for.
They have specific information regarding this subject.
I have not personally contacted, but you may want to as a start.

 

[DougS78]

Thank you all for the information. Those are helpful online resources. I have read some of these, but others are new to me and give more helpful information. My struggle is that everything I can find online is suggestive that it is too small and frankly that our pool builder likely made mistakes along the way with this. Very concerning to say the least. However, given they are not willing to go further (they have offered to have a verbal conversation but not even put in writing the answer to our questions about some of these issues) I suspect that websites, however credible, aren't likely to persuade them.

@AQUA~HOLICS I will see about getting in touch with Janine that you mentioned.

to @ajw22 , no there was no design blueprints or engineer sign off. This was our first pool and we met with the builder, they showed us photos of pools they built. We liked the look of one that had this feature and we asked for a price. In retrospect, we would have taken an entirely different course, but at that time trusted the pool builder to have the knowledge and expertise to provide the pool with the functions they described. As steps unfolded and we became more skeptical we asked lots of questions and I began to learn more about these details regarding sizing.

Needless to say, it has been an exasperating experience and we hope that this pool will function and have longevity, but have some serious concerns.

 

[ajw22]

Unfortunately yours is all too common a story we hear here. Sometimes people find their way here before the build and we can give them the questions to raise before the build.

Consumer protections vary by State and you may need to look into what legal recourse you have. We don't give legal advice here.

If you post pictures of your pool and equipment we may be able to help you brainstorm what could be done to get your pool basically functioning. Maybe the 1" slot needs to be widened? Maybe the trough needs to be enlarged? Maybe you can put in some standard skimmers to absorb some of the flow? Just spit balling some ideas.

I don't know how practical any of the ideas are without seeing your setup. And I would like to understand the pipe flow in and out of the pool and the size pipes that were used.

Do you have pictures of your pool during construction?

Let us know how we can help you more then agree with you that your builder screwed up.

 

[DougS78]

This may not be the “correct method” for calculating this but it gives you the idea of the scale involved. Let’s assume your overflow would need to handle 1/4” of water coming off your surface area of the pool -

20’ X 40’ X (0.25” / 12) = 450 cu ft ≈ 1870 gal

Now let’s assume that your perimeter overflow is such that a 3/8” square of water falls over the edge of the pool -

(40 + 40 + 20 + 20) X (3/8”)^^2 ≈ 126 gal

For a 1/4” square that goes down to 56 gallons

So just doing some very rough bar napkin calculations, I would surmise that your basin needs to hold roughly 2000 gallons of water to be safe AND you would need a MASSIVE sump pump to achieve enough flow rate to move a 3/8” column of water over the entire perimeter edge of a pool that size. Most pool pumps can’t do more than 120GPM of flow rate without some seriously large diameter pipes.

I think your tank and pump are likely undersized for the task.

Small detail, but the 40x20 pool is the inside dimension. the overflow extends a foot on all sides, so that its 42x22 = 924 feet of surface.

The rough calculations I had are as follows:

To raise the surface by 1 inch = 924 x (1/12) = 76.99 cubic ft of water = 568 gallons.

They are stating the weir would be only 1/8" which I (and they) calculate as 9.625 cu/ft = 72 gallons.

Of course, that is just he actual amount of extra water in the pool itself. Whether and how they achieve this precise rate of flow is unclear. They were dialing in the flow to the pump with a manual valve.

I am not sure what you are saying by the "square" of water that falls over the edge. Can you elaborate?

 

[ajw22]

I found the 2 inch rule in this document very interesting...

https://oceanquestpools.com/wp-content/uploads/2022/04/CONTAINMENT-WITH-VANISHING-EDGE-2003.pdf#:~:text=There%20must%20be%20enough%20water%20to%20flood%20the,to%20capture%20splash-out%20and%20water%20lost%20in%20winds.

But there's another way to figure displacement that Phillips and other proponents say is nearly foolproof: The 2-inch rule.

To do this, calculate how much water it would take to replace the top 2 inches of water in the pool, using the equation for figuring out how much water is needed to flood the weir (see sidebar on page 70).

The lower the water level, the less will splash out of the pool, he says. Experiments conducted by Phillips have shown that once the water drops 2 inches, it reaches equalization, a point where the system supplies water as quickly as it can splash out. So no matter how many people enter the pool, or how hard, you can expect it to take care of itself after 2 inches have been displaced.

 

[JoyfulNoise]

I am not sure what you are saying by the "square" of water that falls over the edge. Can you elaborate?

I was just thinking in simplistic geometric terms how to calculate the volume of water falling at the edge of the wall. Rough estimating, nothing more.

 

[JoyfulNoise]

It would be surprising to me that a standard pool pump could supply enough flow rate to move the volume of water required to create a continuous layer of water going over all 4 edges of the pool simultaneously.

Is this pool perfectly level where all edges, end-to-end, have zero difference across the transit? I doubt it. Most pools can easily be off level from end to another by 1/8”. 1/8” difference across a 40ft transit would be an astounding level of accuracy. So even though they are stating that the “weir” is 1/8”, that’s probably far too optimistic an estimate.

 

[AQUA~HOLICS]

 

[JamesW]

To get a 1/8" lift for 128 perimeter feet, you would need about 204 gpm.

A 1/8" lift would put an extra 72 gallons in a 22' x 42' pool.

So, your surge tank capacity would need to be able to hold 72 gallons plus whatever volume of extra water required to keep the pump supplied with water without running dry.

 

[JamesW]

Water in Transit - Water Shapes

Teaching others the principles of vanishing-edge design and construction is something Skip Phillips has been doing for more than a decade. He knows from experience that each setting is different in ways that make it hard to generalize, but nonetheless, h

watershapes.com

 

[JamesW]

Designs with Infinity in Mind - Water Shapes

With all water-in-transit systems — vanishing edges, perimeter overflows or whatever other monikers are used to describe these great watershapes — it's been Paolo Benedetti's experience that all participants need to know what's involved, right from the start.

watershapes.com

Vanishing Edge Pools: Problems and Solutions - Water Shapes

Both structurally and hydraulically, vanishing-edge pools are more complex than the average backyard swimming hole. Here, Scott Cohen delves into a few of the details that most often lead to problems, offering valuable advice on forming, water leveling a

watershapes.com

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

Beyond the Edge - Water Shapes

Visiting the infinitely vanishing possibilities. Book Notes includes reviews of a wide variety of publications hand-selected by a professional watershaper/landscape designer who sees their relevance in his life and work.

watershapes.com

An Edgy Detail - Water Shapes

An inside look at knife-edge overflows. Aqua Culture offers an industry veteran's perspective on the profession of watershaping and what it takes to deal with clients, other professionals and working life.

watershapes.com

 

[AQUA~HOLICS]

I attended a vanishing edge pool training seminar today and here’s one more contact you can try.