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Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/27/2013 9:17 AM

I am planning on building a solar coil collector for my swimming pool using a 3/4 HP sump pump and 5/8" Pex Tubing strapped to 4'x8' black plywood. The tubing is rated for 75 PSI so i want to ensure that the Sump pump will work without cracking the tubing.

The 3/4 HP sump pump has a 1" hose that is 10' long which I will connect to the 5/8" pex tubing. The tubing will be 200' long and will be open on the output end where the warm water will flow back into the pool.

I would like to know how much PSI will be created using these materials.

Any help would be greatly appreciated.

Thanks.

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#1

Re: Total PSI created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/27/2013 9:52 AM

You'd need to find the particulars on your specific pump.

Flow vs pressure mostly. Total head, etc.

Start with the pump maker's website, or nameplate on pump and flow curve.

Also you'll need some idea of the elevation change.

Then there's the heat absorption quality of the tubing to consider.

Excessive pressure probably won't be a concern. Rate of flow vs heat absorption of water through the tubing is a consideration, too.

Build it, put a throttling valve on the output of the pump and experiment.

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#2

Re: Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/27/2013 12:03 PM

It would probably help to manifold the PEX tubing into four parallel runs of 50 feet each. This will better match the flow of the pump. You could also get by with less HP.

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#3
In reply to #2

Re: Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/27/2013 12:13 PM

Yep.

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#4
In reply to #2

Re: Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/27/2013 12:42 PM

Like Lyn sez, yep. Since the water is flowing back to the source, a lot of energy is recovered. Use a large pipe from the pump to the manifold, have throttling valves on each fifty foot run so they all get the same amount of water.

Solar hot water heaters have very small pumps. You don't want the water going too fast, it won't have time to get hot.

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#5
In reply to #4

Re: Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/27/2013 12:48 PM

If the runs are the same length/configuration, they will naturally balance to equal flow without needing valves.

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#6

Re: Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/27/2013 2:05 PM

Sump pumps are typically high volume low pressure pumps. Odds are it doesn't do much over 15 - 20 PSI and are very inefficient water movers when running at near dead head back pressures and low flow rates.

3/4 Hp is gross overkill and a total waste of energy for doing such a small circulating job.

What you need is a normal hot water heat circulator pump. A properly sized circulator pump for what you are doing would likely only be using 50 - 100 watts at the most.

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#7

Re: Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/27/2013 2:20 PM

The pump may not be your biggest problem. All PEX I'm familiar with should not be installed in UV (sunlight) exposure. Regular black polyethylene pipe might last about as long, but it too tends to crack with age.

From Wikipedia: "Degradation from sunlight. PEX tubing cannot be used in applications exposed to sunlight, as it degrades fairly rapidly. Prior to installation it must be stored away from sunlight, and needs to be shielded from daylight after installation. Leaving it exposed to direct sunlight for as little as 30 days may result in premature failure of the tubing due to embrittlement.

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#8

Re: Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/28/2013 3:31 AM

The operating point in the pressure/flowrate plane is where the pump performance characteristic curve and the system characteristic curve intersect. Not knowing the shape of either curve, it is impossible for the forum to determine the full answer to this question.

Overpressure downstream of a pump can be prevented by using appropriately-sized pressure relief valves, however it is usual for the downstream piping to be strong enough to withstand the dead-head pressure of a pump, thereby making the provision of pressure relief unnecessary.

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#9

Re: Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/28/2013 8:33 AM

Apart from all of the other relevant answers, it would want to be a really small swimming pool for you to gain any benefit from such a small collector.

It is generally acknowledged that a swimming pool solar collector needs to be roughly equivalent in area to at least 60% of the pool surface area (dependant on local insolation, wind loads, pool cover etc.).

I would also suggest using a smaller diameter pipe in multiple parallel runs, as it is the surface of water exposed to the sun which does the heating, and more, smaller pipes will expose more water for greater benefit without reducing the flow rate too much.

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#10

Re: Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/28/2013 9:55 AM

Having many sump pumps in my time I cannot imagine one that can create enough flow with restriction to achieve 75 PSI.

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#11

Re: Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

05/28/2013 10:38 AM

I have considered a similar plan except to use a manifold with up to 250 feet each of low pressure black irrigation line which is available in 1000 foot rolls and can weather the sun very well. Also I would use a white reflective surface in hopes of getting more reflected light onto the backside of the black plastic for improved heat gains. However after thinking about dealing with that much plastic and the likely kinking problems I have yet to try. It is however very cheap to buy about $150 US dollars/1000 ft.

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#12

Re: Total PSI Created from a 3/4 HP Sump Pump in 5/8" Pex Tubing

06/01/2013 11:34 PM

Beware the maximum temperature inside a solar collector can get above 100C (212F), and thus would be too hot for the PEX to retain its strength. I would choose copper, and paint it black, then cover with a layer of glass. Even in Scotland this damaged connection pipes made from domestic hot water feed pipes for a washing machine (rated for 95C).

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