Costa Rica Pool/Spa schematic and questions

[Aaron B.]

Hello all,

I am living in Costa Rica, and in the process of building a B&B in the jungle.
We have been working on the design for quite some time, and I am now looking at the pool schematics.

Most professionals around here are not interested in doing a proper analysis or studies. So we have taken it upon ourselves to make the best possible pool system for our area/climate.

I have browsed through this forum and other places on the internet for most info, and compiled it into the attached schematic (which I can't seem to upload any bigger).

An important part of building in the jungle is maintenance, and trying to go back to 'simple' solutions. We like to steer clear of complicated electronics, or automated solutions. Not because we do not like them, but because things tend to break quickly here, and fixing them means ordering replacements from the States, that take weeks to arrive.
We are 2 km from the ocean, in the middle of the rain forest. We run most things on solar panels, but the grid connection supplies heavy users. This means this equipment gets treated to terribly 'noisy' electricity with lots of spikes.

POOL SETUP:
The main setup is a 20.000 gallon pool, with an infinity edge and a separate (heated) 2.000 gallon spa.
I calculated the total dynamic head loss at 30 ft, but a dry start also requires overcoming a 36 ft head, as the spa is located higher on the mountainside.
I have not found much information for exact TDH calculations, so am not sure if this is completely accurate. And theory and practice will be somewhat different supposedly.

We would like to run this on a 3/4hp pump like a HAYWARD Tristar SP3207EE or something similar. Most important is a pump that's simple. We have lost fancy pumps the terrible electricity here.
With a 2x daily turn over, we would need 28GPM of flow if running the pump 24hrs.

This pump could theoretically push about 100GPM at 30 ft head, but going down to a smaller pump, I can't overcome the additional head of the dry startup.
I prefer to keep the pump as small as possible, but can't find a solution that can overcome both problems.
Looking at the chart, I'd say, go for a 2 speed pump, but none of the 2-speeds seem to be able to overcome the normal runtime 30 feat head...
So I'm a bit stuck here...

I also read a lot about overdimensioning sand filters and salt water generators, so am not sure what would be the best size now.
I am thinking a 3.69 sqft. sand filter, which would allow up to 74GPM according to the 101hydraulics, and a hayward aquarite 9-cell?

We have plumbed the sand filter to backwash using springwater (we have free and abundant water), to avoid dumping treated water.

SPA:
Further on, I have plumbed the spa drain with a syphon, to prevent it from draining into the pool when the pumps are out. Communicating barrels and all...
Perhaps there is a better solution for this? On the return side, I can place a no-return valve.
The spa also has an extra pump for spa jets. Which can be turned on from within the spa. This powers a loop pipe of 2" piping, which sucks air through an air pipe of 1.5" that has a syphon in it above pool level.
It has 2 three-way valves to turn run through the collector or heater. We are not sure yet which would work best. Perhaps the solar collector will be enough in our climate, but we'll have to see what happens there.

INFINITY EDGE:
The infinity edge return has a separate pump, as it seems this is the only way to solve this. The buffer tank is a concrete tank in the pool room, as we don't like to build a big and wide collector next to the pool.
The pool overflows into a small ditch with a stainless steel mesh that holds out large debris. It flows into two 2" pipes that gravity feed the 1.500 gallon buffer tank.
The buffer tank has an overflow for storm and rainwater. It is a non-pressurized tank, and has an air intake to prevent vacuum. It uses a float valve to fill up the pool water in case of spill or evaporation.
I was thinking of running this pump with an IR sensor, to only turn on when there are people around and in the pool. But maybe there are better solutions for this as well. I've read about sensors to control pool level. But again, am skeptic, as I try to stay the easy fix, low tech course...


So, to summarize:
We try to design our pool with 'simple' technology.
- I'm not sure about which pump to pick, I believe I have all the info, but can't seem to find a low-tech, energy efficient pump that does what I need.
- I am not sure about over or under sizing the sand filter and SWG, and as I cant pinpoint the pump, I can't determine the exact flow.
- I am not sure if the plumbing solutions I have chosen for the spa will work well.

I hope someone can give us some input on what would work best, and that this may help others with a similar setup.

 

[mas985]

Welcome to the forum!

First a couple of comments.

Forget about head loss, it is very difficult to calculate accurately and it depends on the pump that put on the plumbing. But more importantly, it usually doesn't matter much except maybe for spas but there are other ways to design for that.

Forget about turnover. There is not magical turnover number for a pool. Some run at 1/4 turn per day others more, other less. There is no real correlation between turnovers and a healthy pool. This is why you really don't need to know head loss because you don't really need to know flow rates.

This pump could theoretically push about 100GPM at 30 ft head, but going down to a smaller pump, I can't overcome the additional head of the dry startup.

Not sure what you are talking about here but the head loss number you have for 100 GPM is WAY WAY too low for typical plumbing. I suspect you are not calculating it correctly. As I mentioned before, it is not easy to do and head loss is dependent on flow rate so a pool with typical 2" plumbing will have over 80' of head loss at 100 GPM. But why does any of this matter? Is the pump significantly above water level?

I am thinking a 3.69 sqft. sand filter, which would allow up to 74GPM according to the 101hydraulics,

The flow rate is really an upper limit recommendation. The filter would "allow" much more flow rate than that but then it might not work properly.

Further on, I have plumbed the spa drain with a syphon, to prevent it from draining into the pool when the pumps are out.

Not sure what you mean by this but most pools use check valves to prevent draining of the spa into the pool.

The spa also has an extra pump for spa jets. Which can be turned on from within the spa. This powers a loop pipe of 2" piping, which sucks air through an air pipe of 1.5" that has a syphon in it above pool level.

IMHO, the pipe is way too small for a spa unless you only have a couple of jets. How many jets do you have and what is the flow rate requirement for the jet?

The pool overflows into a small ditch with a stainless steel mesh that holds out large debris. It flows into two 2" pipes that gravity feed the 1.500 gallon buffer tank.

Generally, the plumbing to a balancing tank are quite large in order to handle the flow rate. Remember, the gravity fed flow rate has to be as high as the pump flow rate which is probably going to be quite high in order to get the edge effect you want. Is one of the lines directly from the pool? How deep is the tank relative to the overflow basin?

 

[Aaron B.]

Thanks a lot for your suggestions Mark.

From your comments I understand it is very hard to calculate things beforehand.
What pump would you suggest for a setup like ours? I'd love to have a variable speed pump, so we can change things depending on our needs, but I'm afraid they're too high tech for our location and noisy electricity.

Generally, the plumbing to a balancing tank are quite large in order to handle the flow rate. Remember, the gravity fed flow rate has to be as high as the pump flow rate which is probably going to be quite high in order to get the edge effect you want. Is one of the lines directly from the pool? How deep is the tank relative to the overflow basin?

The overflow from the infinity edge goes directly to the buffer tank, which is located about 15ft lower. I have two separate direct lines. I could make them 4" or so to allow for more flow.
I understand there is some required flow to make the water flow over the edge properly. Is there a formula to determine required flow, based on the length of the infinity edge?
Would this then be considered the parameter on which to determine the pump, flow, and diameter of the pipes?

Not sure what you mean by this but most pools use check valves to prevent draining of the spa into the pool.

What about the bottom drain of the spa? I can't put a check valve on the outlet, as it's supposed to go that way... ? If the pipe is full it will flow into the pool until both are at the same level (communicating barrels)? Which means it will lower the level in my spa to the pool level when pumps are out.
If I put in a curve in the piping, that goes up to the water level of the spa, and pumps are out, this 'siphon' will overflow until the level of the curve is reached, and stop draining the spa.
Or am I completely off, and do you not install a bottom drain in a spa? Or do you connect it to a skimmer for the same effect?

IMHO, the pipe is way too small for a spa unless you only have a couple of jets. How many jets do you have and what is the flow rate requirement for the jet?

I was thinking about 4 jets. It's a spa for 2 people.
Not sure what flow I need, I guess it depends on the type of jet and the effect I want? I'm trying to learn as much as I can.

I appreciate all the help, thanks!

 

[mas985]

I understand there is some required flow to make the water flow over the edge properly. Is there a formula to determine required flow, based on the length of the infinity edge?
Would this then be considered the parameter on which to determine the pump, flow, and diameter of the pipes?

Yes and yes. It depends on how level you can make the edge. If the edge is within 1/8" and you want 1/8" over the highest point, then you will need at least 5 GPM per foot of edge. A sloppier edge is going to require more flow rate.

The buffer tank is a concrete tank in the pool room, as we don't like to build a big and wide collector next to the pool.

Have you done a proper surge analysis to make sure the trough is both deep enough and wide enough for large water surges? Active pools require fairly large troughs even with surge tanks.

All of these things are quite critical so you might want to get a professional involved to make you are sizing things properly. An infinity pool design is not for amateurs.

What about the bottom drain of the spa? I can't put a check valve on the outlet, as it's supposed to go that way... ? If the pipe is full it will flow into the pool until both are at the same level (communicating barrels)? Which means it will lower the level in my spa to the pool level when pumps are out.

There are three modes for a pool/spa combination controlled by three way valves on the various suction and return lines. Pool mode (pool suction, pool return), spa mode (spa suction, spa return) and spillover mode (pool suction, spa return). Only the later will drain water from the spa to the pool when the pumps shut off. But you can stop that with a check valve on the spa return pipe.

Not sure what flow I need, I guess it depends on the type of jet and the effect I want? I'm trying to learn as much as I can.

Yes, you need to decide on the jets first.