16 July 2024 Finishing Up my OB Pool

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setsailsoon said:
I can do that but will require some plumbing changes. I have 3 suctions - infinity basin, main pool, spa.
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To heat the spa with the filtration system and run the jets with the 5 hp pump, you would need 2 spa suctions and 2 spa returns.

I would change the filter pump to 3 hp and install a 3.5 lb check valve bypass on the heater.

The check valve will stay closed until the water flow through the heater hits about 48 GPM and then it will begin to open.

At 120 GPM, you might have about 50 GPM through the heater and maybe 70 through the bypass.

Use a heater flow switch to be safe.

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JamesW said:
To heat the spa with the filtration system and run the jets with the 5 hp pump, you would need 2 spa suctions and 2 spa returns.

I would change the filter pump to 3 hp and install a 3.5 lb check valve bypass on the heater.
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My original plan (right or wrong) was to have the heater and swg on the 5 hp circuit. And use the filtration pump separate. So no filter on the heater and swg. Now after all the comments I think I should run them on the spa and pool circuit and keep the 5 hp for only the infinity and zero edges. I think I'll see how the 1.5 hp pump performs in this service and if needed upgrade to 3 hp.
 
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JamesW said:
It really depends on how much lift you want.

That's a subjective decision.

You might be happy with 1/8" and you might prefer 1/2".

You might be able to put both pumps on the 4" line and run them both at full speed and that is the best you can do and the flow is what it is.

It depends on where the pumps will begin to cavitate and what the actual head loss is on the suction and return.

If the pumps cavitate at full speed, you will need to turn them down until the cavitation stops.
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This is one of those things where bigger is definitely better.
 
By my estimates, with the heater in line the flow rate should be about 130 GPM at full speed which is a little above the 120 GPM manufacture specification. So an RPM of 3100 should keep it below 120 GPM. That would be around 7/32" over the edge.

The edge should be obscured due to reflections on the surface of the water. Water is very transparent so without any reflections, you will probably always see the edge no matter how deep. After all, you can see the bottom of the pool right? The only time you can't see the bottom is when the reflections off the sky prevent it.
 
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Absolutely. However, most of what you see at shallow angles is the reflections from objects above the water line and very little below the water line.

This is exactly what you would expect from the scattering of electromagnetic waves (i.e. Snell's law). The shallower the angle, the higher the reflection coefficient and the lower the transmission coefficient. At shallow enough angles, you won't see anything under the water due to the critical angle.

en.wikipedia.org

Snell's law - Wikipedia

en.wikipedia.org en.wikipedia.org

Take this picture. The further away, the more reflections you see from above the water line. The closer to the observer, the more you see underneath the water.

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An angle like this and you really can't see anything under the water:

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Here is another with a better mix. Some of the edge you can see while others you can't see.
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mas985 said:
By my estimates, with the heater in line the flow rate should be about 130 GPM at full speed which is a little above the 120 GPM manufacture specification.
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That will damage the heater.

It will cause excessive pressure and it will strip the copper in the heat exchanger due to excessive velocity.

Also, dirty water can clog the internal bypass and the thermal regulator.

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We must be getting a heck of a lot of flow out of the big pump. I am measuring between a quarter of an inch and 5/16 all the way almost all of it is right at 5/16. We do have a slight breeze blowing in across the pool. But even the infinity edge has 5/16 of an inch. This is without closing the gutters off. Maybe I'm getting more flow then I should be through the heater? This is without an external bypass I wonder if it has an internal bypass? I don't think it does, I will double check.
 

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setsailsoon said:
We must be getting a heck of a lot of flow out of the big pump. I am measuring between a quarter of an inch and 5/16 all the way almost all of it is right at 5/16. We do have a slight breeze blowing in across the pool. But even the infinity edge has 5/16 of an inch. This is without closing the gutters off. Maybe I'm getting more flow then I should be through the heater? This is without an external bypass I wonder if it has an internal bypass? I don't think it does, I will double check.
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What RPM are you running at?

How are you measuring it? That can influence the depth.
 
JamesW said:
That will damage the heater.

It will cause excessive pressure and it will strip the copper in the heat exchanger due to excessive velocity.

Also, dirty water can clog the internal bypass and the thermal regulator.
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So then why do they also suggest a maximum flow rate of 120 GPM in the heater manual. Forgot tom mention that if you run at 3100 RPM, the flow rate is below 120 GPM. This is what I actually had posted:

By my estimates, with the heater in line the flow rate should be about 130 GPM at full speed which is a little above the 120 GPM manufacture specification. So an RPM of 3100 should keep it below 120 GPM. That would be around 7/32" over the edge.
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Also, keep in mind that most of that flow rate gets bypassed in the internal bypass and does not even go through the heat exchanger.

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The copper looks to be about 3/4" diameter.

At 120 GPM with half going through the internal bypass, that puts the flow at about 15 GPM per tube, which is 9.5 feet per second.

To get below 6 feet per second, you need to drop below about 80 GPM.

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At 120 GPM with half going through the internal bypass
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How do you get 50%? If you look at the flow path, both the bypass and the loop path have valves. The loop path valve is a thermostat and from pictures, looks to be much smaller than the bypass valve. But still, if you even consider them the same, the loop path would have head loss in the loops and the thermostat while the bypass would only have head loss in the valve. So to me, it would seem logical that the bypass path would have much lower head loss than the loop path.


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It's hard to tell exactly how the water will split between paths.

In any case, it creates more pressure, stress and copper erosion.

In my opinion, it preserves the life of the heater if you keep the flow well below 120 gpm.

I would suggest 80 GPM as an upper limit, but I don't have any hard data to support that number.
 
How does the flow look at full speed?

How loud is the pump at full speed?

You can add a vacuum gauge and a pressure gauge to see what the head loss is.

You can add a flowmeter to see what the flow is.
 

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