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DIY solar pool heater

PostPosted: Thu Nov 05, 2009 5:01 pm
by rob_hi
G'day all,

I'm toying with idea of building my own solar hot water heater for my pool. I'm no expert on solar heating of water and might be barking up the wrong tree with my idea.

Having experience of backyard greenhouses and conservatories in cold climates, I know that they can become extremely hot even on a cold (<10c) day, so why not put solar collecting pipework inside a glass box ?. Direct exposure to the sun through glass would boost the heat significantly (according to my anecdotal evidence) compared to being exposed to the same sunlight but also the ambient air temperature and cooling breezes.

I reckon a long length of thin copper pipe (max pipe surface area per volume of water) in a "glass heat box" would bring the water up close to the air temperature in the box (40c + on any sunny day).

Anyone tried anything similar ?

cheers,
rob

Re: DIY solar pool heater

PostPosted: Thu Nov 05, 2009 5:40 pm
by Gordon-Loomberah
Some relations of mine used a big roll of black poly pipe to heat their pool back in the 80's. It worked quite well and cost very little to set up.

Gordon

Re: DIY solar pool heater

PostPosted: Thu Nov 05, 2009 7:43 pm
by Tracker
Yes - I have seen that done too..
just a big roll of poly-pipe and then spread it out like a spilt, pile of coins
(exposing all the loops) and then tie it down.. Aint beautiful but it works..
The neighbors can be told it's an "Artistic Creation" called the "Carbon Cycle"

Re: DIY solar pool heater

PostPosted: Fri Nov 06, 2009 10:45 am
by rob_hi
Gordon-Loomberah wrote:Some relations of mine used a big roll of black poly pipe to heat their pool back in the 80's. It worked quite well and cost very little to set up.

Gordon


A roll of polly pipe was/is my plan A, I just thought it'd be more effective to put the pipe under glass too, and then I worry that polly pipe would melt under glass.

Maybe I'll stick with plan A to begin with.

Re: DIY solar pool heater

PostPosted: Fri Nov 06, 2009 12:00 pm
by Tracker
Dont know that it would MELT, especially is water was flowing through it....!

Would be easy to make "Neat"

Build a pergola - Cover with Shade Cloth - ( Black Woven, 90% )
Spread the roll out over the pergola and down to the pool.

Unless the Mother-In-Law arrives by Helicopter, there will be no complaints..

GLASS ?-? A whole new dimension in expense and maintenance..

For the cost -- Plan A -- Wins hands down

Re: DIY solar pool heater

PostPosted: Tue Nov 10, 2009 7:36 am
by dynamictiger
Not to rain on your parade.

The copper idea is great for producing high heat water in small amounts. However the issue is pool heating requires loads of low energy to effect a temperature change.

Copper is also not the material of choice for pools. Chlorine attacks copper, and whilst in some instances e.g. gas heaters, copper is by default used, the copper often only lasts a few years before complete failure.

The poly pipe idea is more efficent for heating pool water however the heating outcome will depend on flow rates as well as area. Too high a flow rate won't add a lot of heat to the pool although it may make the water in the coil hot.

Of the two choices poly pipe is a better option. It is cheaper to build and would most likely be more effective at adding some temperature to the pool. However poly pipe is not made for pool water and will also degrade in a short period of time. I cannot be certain on the time line on this however given the price it probably doesn't matter.

Re: DIY solar pool heater

PostPosted: Tue Nov 10, 2009 8:23 am
by rob_hi
dynamictiger wrote:Not to rain on your parade.


rain away. You might save me a whole heap of trouble.

Polypipe it will be.

Re: DIY solar pool heater

PostPosted: Tue Nov 10, 2009 10:22 am
by duendigger
I had 2km of 1/2 light wall polly pipe ( the black stuff you use for low pressure watering of gardens ) siting on our veranda roof. I has the ends manifolded to balance the flow.

It worked a treat. Got the pool up to 37 degrees on one occasion before everybody said 'enough' ! If we had a solar cover on the pool it would have been a LOT hotter

Sadly we put on another story on the house and it was too difficult to relocate

Dunedigger

Re: DIY solar pool heater

PostPosted: Tue Nov 10, 2009 12:37 pm
by countrykid
The poly pipe idea is the way to go I think because it is cheep and easy to handle.
The trick to how good it will work is the length of pipe and the flow rate of the water.
The longer the pipe, the more water there is to heat.
If you have a shed or house near, put it on the roof.
Tap into your filtration system on the return side with a T connection,
and have a valve to control the flow rate.
Test the temp. at the outlet and adjust flow so that it is not too cold,
and not too hot either. Too hot will kill the chemicals.
Happy dipping.
Country-Kid.

Re: DIY solar pool heater

PostPosted: Tue Nov 10, 2009 1:52 pm
by FamilyMan
I bought the biggest roll of large diameter (I can't remember whether it was 25 or 35mm) irrigation black poly pipe and wound it into a big spiral so the gap between coils was about the same as the diameter of the hose. This meant that regardless of the angle of the sun through the middle hours of the day, about the same amount of hose was exposed constantly. I am in Brisbane and I achieved basically 1 degC per hour for 1000 litres per square metre of hose area. That is pretty close to the theoretical maximum for memory - certainly close enough for the money I outlayed. If you don't run the pump the water temp in the hose peaks about 70degC, so the previous comments about the chemicals means you would want to keep the pump running to keep the temp down. I was only heating a spa so my 1000 litres could be heated to 40degC in about 4 hours in summer with 4m2 of hose. A rule of thumb I have heard is that you want to have around 150% of the pool surface area as heating area (in Brisbane). Obviously more area gives you better performance and a longer swimming season into winter. A pool cover to minimise heat loss overnight also helps.
So, say your pool is 12x4m, and averages a little over 1m deep, to give you 50000litres, 70m2 of hose (25mm hose x 2800m, yes 2.8km) would give you about 1 x 70 / 50 =1.4 degC per hour peak rate of heating. You get about 6 hours of this in summer and about 4 hours in winter.

My heater never failed, or sprung a leak in about 5 years before the spa was decommissioned. Black poly pipe is good stuff. Don't underestimate the logistics of handling that amount of pipe, and remember that if laid close together, the black hose will weigh about 20kg/m2 when full of water, so don't underestimate the roof load.

Also remember that pumping water to the roof comes at a cost in electricity. Putting all of the pipe in one run is a good way to throttle back the pump output, reducing your flow rate, but be careful to not exceed maximum pressures. I put my heater coil upstream of the filter so the filter cannister was not handling the increased pressure. It also has the advantage of not needing to buy many connectors. However, for a great length of hose, you may need to adjust the number of series vs parallel runs to get the flow rate vs pressure reasonable. Remember also that the radiated losses from the coil will be dependent on the exit temp of the heater, so better to aim to keep the heated water entering the pool at around 35-38deg so you don't waste a lot of that heat you have gathered.

A good fun project with lots to think about.