Heating my kids pool - physics question.

[Nuro]

I recently got my 2 year old a blow up splash pool. I'm now hatching a plan to heat it using the sun.

My idea is to buy a garden hose, roll it up into a big spiral, and paint if with some form of durable black paint, stick it on the roof.
Both ends of the hose will be submerged in the pool, and the hose filled with water, so that the hose system will be air-free. I will then use a simple fountain pump to circulate water in the hose system.

My question is, considering that the heating loop is closed, do I still need such a strong pump? With a fountain, the water has to be pumped all the way to the top, into a open system, so the energy of the water moving down is lost. I'm hoping that with a closed system, the water coming down again will negate the need for a very strong pump. Or am I missing something?

I don't need the water to flow quickly, just circulate slowly.

 

[Valis]

The water circulating doesn't make any difference, you still need a pump strong enough that can pump water to the height of the roof. Also, unless you keep the pump running 24/7 or dump masses of chlorine in the pool your hose will soon be clogged up with algae.

 

[Carbon_Fibre]

How many litres is the splash pool?

I have solar heating (2 panels) for my 6x4m pool. Last year I thought about tinkering with the current system to include some copper pipes. But by October the pool temperature shot up to about 28 degrees. This year the warming of the pool water seems slower even though the (air) temperature feels hotter than last year. It's only at 20 degrees.

 

[porchrat]

The water circulating doesn't make any difference, you still need a pump strong enough that can pump water to the height of the roof. Also, unless you keep the pump running 24/7 or dump masses of chlorine in the pool your hose will soon be clogged up with algae.

+1 your pump still needs to push that water against gravity up onto the roof.

If you're going to do it you need to get a pump with the appropriate "head pressure".

"Head pressure" on the other hand is more complicated. "Head" may be simply defined as any resistance to the flow of a pump. When pump manufacturers list the head pressure, they are referring to the vertical discharge pressure head. Described in very simple terms, a pump's vertical discharge "pressure-head" is the vertical lift in height (usually measured in feet of water) at which a pump can no longer exert enough pressure to move water. At this point, the pump may be said to have reached its "shut-off" head pressure. When you look at a flow curve chart for a pump, the "shut-off head" is the point on the graph where the curved line becomes horizontal as the flow rate at that point is zero. The higher a pump's head pressure, the more powerful the pump.

You need to be sure the pump can actually get the water up onto the roof. Obviously if you keep the pipe lower then this isn't so much of a problem.

Those little blow up splash pools usually have a relatively small volume of water anyway. Doesn't the sun alone heat it up enough?

 

[Nuro]

Ok. I was hoping the head pressure would be lowered by the water returning down the hose, sort of like siphoning petrol from a tank with a hose. But strong pump it is
The pool is 2.5x2.5x.3, so about 1875 litres. I was going to do it as a weekend project, but will put it on hold

 

[BrokenLink]

Why do u actually need to pump it onto the roof? The sun on the ground and roof is the same.....its just usually placed on the roof to be out of the way. Might be easier just to find a sunny spot near the pool? Orconnect it to a small piece of copper pipe over the braai, pump it through that with a fire underneath

 

[HavocXphere]

Roof = 3m. The type of pump needed to do that is pretty strong & draws a lot of juice canceling any gains made by using solar.

I'd recommend: Fill pool 1/2 w/ tap water. Wait till it moves from tap water temp to air temp & top up with geyser hot water. You just need to take the edge of it so no need to use only geyser water. For kids in a splash pool a proper solar solution is overkill imo.

You're also missing a couple of tech challenges that will crop up. e.g. a painted gardenhose is about as close to perfectly insulated as it gets...it won't transfer the heat to the water effectively.

Some hoses also leech chemicals when the encounter heat. Not sure about garden hoses, but some do. Given that there are kids involved :/

OT @ tech people here: Wouldn't one of those old school fireengine style pumps require a lot less power for this type of application than the fan blade designs?

 

[alphabyte]

Hi Nuro, This is something I have never tried, so I cannot talk from experience.
BUT: common sense says to me that you are right in your assumption that the water flowing down from the roof in effect sucks up the water from the pool to the roof, i.e. a siphon effect, exactly as you say. So your pump only has to be strong enough to overcome the resistance of the water flowing through the hosepipe; the height does not come into it. Maybe you can borrow a small pump from somewhere to give it a try? Good luck.

 

[Nuro]

So it is a bad idea. But the pump question interested me

@alphabyte, I have an old pump with about a 2m head. Will try it with a bucket and see what happens.

 

[arf9999]

The water circulating doesn't make any difference, you still need a pump strong enough that can pump water to the height of the roof. Also, unless you keep the pump running 24/7 or dump masses of chlorine in the pool your hose will soon be clogged up with algae.

If you have a simple filter on the inlet it'll be unlikely to clog. There won't be any algae build up in the pipe itself because there isn't any light. Any algae would come from the pool itself. It's a blow up kiddie pool, if it starts getting ugly, just empty it and refill.

 

[ponder]

Put something with a black surface at the bottom of the pool. Rather buy black plastic pipe which you could either put on the ground or roof and circulate the pool water through it at a slow rate, this way you need a smaller pump using less juice.

 

[Leostar]

Lay black pipes used by farmers for irregation. Also lay pipes below paving stones so no need to lift water. The paving stones might not conduct enough heat though? Build a jacuci/sauna next to pool and lay pipes on the lower roof?

 

[UnUnOctium]

Hi Nuro, This is something I have never tried, so I cannot talk from experience.
BUT: common sense says to me that you are right in your assumption that the water flowing down from the roof in effect sucks up the water from the pool to the roof, i.e. a siphon effect, exactly as you say. So your pump only has to be strong enough to overcome the resistance of the water flowing through the hosepipe; the height does not come into it. Maybe you can borrow a small pump from somewhere to give it a try? Good luck.

<- this. only problem is initially getting the water up the roof, once you have full flow in a closed loop system with almost no air in it, the power it will need is only dependent on the height difference between the pump and the end point. The problem is at the start you need to have enough energy to get the water up the 3 m. This is the same as when you siphon petrol, you just need to suck so that you provide enough power to get over the peak height and then you keep the end point lower than the starting point.

 

[werries2]

Use black irrigation pipe, dont waste money painting a normal hose pipe... Category 3 or 5 pipe they have thiner walls so that you heat up the water faster.
Also use a pipe with a small diameter (~15mm should be perfect), the smaller the diameter the higher the surface to volume ratio become and you have more efficient heat transfer.
With the smaller pipe and lower volume it will also be harder to get air bubbles in the system that would nullify your siphoning effect.
Fill the pipe with your residential water pressure (~3bar is eneugh to pump water 30 meters into the air!).
Place your pump with a non return valve before it at the end of the pipe (just before you let the water back into the pool). If the water runs freely into the swimming pool you will form air pockets in the pipe, by placing the pump at the end of the pipe this should not be a problem.
Just take care the water in the pipe can get incredibly warm!

Alternatively and possibly cheaper just buy a black plastic cover for your pool and let the afternoon sun do its trick on the water directly.

 

[AstroTurf]

Buy one of those water heaters for camping, kettle element in an enclosure.
It will warm the pool up enough in about 15 minutes.

We have a 3.5x3.5meter above ground pool in direct sunlight, in Summer it gets to hot in my opinion so if you put the pool in the sun it will heat itself enough pretty quickly.

 

[ponder]

<- this. only problem is initially getting the water up the roof, once you have full flow in a closed loop system with almost no air in it, the power it will need is only dependent on the height difference between the pump and the end point. The problem is at the start you need to have enough energy to get the water up the 3 m. This is the same as when you siphon petrol, you just need to suck so that you provide enough power to get over the peak height and then you keep the end point lower than the starting point.

Something here is fishy. The end point will have to be in the water at a lower level which has higher pressure. Perpetual motion?

 

[UnUnOctium]

Something here is fishy. The end point will have to be in the water at a lower level which has higher pressure. Perpetual motion?

I forgot to add that for a closed system it makes no diff Was thinking of an open system at the time (which you get potential energy due to the difference in heigh between the 2 water containers).

 

[shogun]

Use black irrigation pipe, dont waste money painting a normal hose pipe... Category 3 or 5 pipe they have thiner walls so that you heat up the water faster.
Also use a pipe with a small diameter (~15mm should be perfect), the smaller the diameter the higher the surface to volume ratio become and you have more efficient heat transfer.<snip>

^^ This is your best advice. My dad did this as an experiment. The pressure is your main problem, but the irrigation piping works a treat and the water coming out is BLERRY hot if the flow is slow enough. The smaller diameter tubing might be better from a heat pickup... but be careful you don't pump the water through it too quickly. Stay away from a regular hose and paint... that's a mess for very little gain (garden hoses are perhaps a bit thick, and insulated for this task).

 

[wise_guy]

What pump are you planning to use?Have you considered a washing machine pump.

 

[clintoncoetzee]

you dont need a massive pump, take this into consideration : you have for arguments sake 2L of water in the pipe eading for the roof ,2L = 2kg , and you have 2L in the pipe coming back down,2L=2kg ,its balanced until you add something to tip the balance one way ie:your pump . i would even say a slower pump is better as the water has more time to heat up in your pipe.
hope this helped