A challenge - Solar heating for free?

[Nick]

Well it's OK for many of you good people, you are lucky enough to live in a climate where your pools warm nicely throughout the day But for me, being stuck in Blighty our pool is further north than all the US states except Alaska so the amount of solar benefit (even with a solar cover) is not brilliant.
Last year we actually managed to gain a 5 degree advantage using a solar cover during the hotest part of the summer and it even got warm enough to get my 2nd daughter in the pool last year. But this year I would like to try and get more heat in to the pool so I started looking at heating options including gas, oil, solar panels, heat exchangers etc but I need to heat the pool on a low budget and all the other options are quite expensive

So, here's the challenge I have set myself.

To design, source and build a self contained fully operational and effective solar water heating system for the pool without spending a single penny on any materials at all.

My design concept is to capture and convert solar energy in to usable water heating by using four old radiators donated by my sister who recently had her central heating system replaced.
The four radiators will be mounted on old chip board and wood panels etc which I am collecting from various sources for free. I will then connect the radiators in series using old pieces of copper tubing, washing machine hoses, old tap hoses and plumbing fittings I have lying aroung in the shed and will paint everything black in order to (hopefully) attract the maximum amount of solar energy. Then the radiators will be encased in common polythene sheet to provide an additional 'greenhouse' effect.
I'm looking to mount the radiators on a sun facing wall at an angle that shound maximise the suns rays.

Will it work? I have no idea.
But I'm looking forward to playing around with it and finding out. If it doesn't at least I have lost anything.

As things kick off I will try and post some pics so you can all have a good laugh at the endevour.
Don't build your hopes up, I know I certainly am not. It will just be interesting to see what improvements (if any) it makes

If anyone has any ideas, suggestions and criticisms then pease feel free to chip in as I'm totally open to comments good or bad

 

[Guest]

old pieces of copper tubing,

probably not a good idea unless you don't mind the possibility of copper stains in the pool. Not saying it will happen but it can!

 

[JasonLion]

For solar heat you want to maximize the surface area of the collectors. Radiators are not the ideal thing for heat exchange, they are designed for high temperature differences between the water and air, while for pool heating you want to run at low temperature differences. For low temperature differences, you want as much surface area as you can manage and relatively thin walls. Radiators will certainly work to some extent, but there are plenty of things that would be better. I don't know exactly what you can get for free, but lots of small thin walled tubing is ideal.

When using things that were free you need to pay some attention to what they have held in the past. You don't want to contaminate the pool with anything if you can possibly avoid it, so clean everything well before using it on the pool.

 

[Malcolm]

You may want to connect your radiators in parallel, not series. The amount of heat transfered is proportional to the temperature difference, so you'll want to get the water out of the solar heater before it heats up too much.

 

[Nick]

Thanks for the suggestions.
I took them all on board but unfortunately I failed in the challenge.
I was so close to having free solar but the one sticking point I had was a pump. I couldn't find a pump for love or money. Originally I tried using the existing 500 gallon Intex pump but going from 1.25 inch to 1/2 inch was impractical without spending loads on fittings to do the job. It needed too great a head of pressure for a bodged job to handle.

In the end I forked out for a small water fountain pump from a nearby pond store. Total cost £15.00 (about $20.00 I think). The pump feeds cold water straight from the bottom of the pool and pumps it out using common garden hose to the black painted radiators. The rads then return the water by garden hose to the filter sock we use.

The net result isn't amazing, but it has proved to me that it can be done and it can be improved upon. Now I just need to start polishing off the design a bit.

At the moment it's a sunny day, the pool temp is 71 and the water from the radiators is a nice 93 ^oF. Air temp is about 20 ^oF. The flow rate of the pump is about 102 litres per hour.
When I reduced the flow rate to about 30 litres per hour the water temp hit a scorching 115^o


I had to go for the serial connection instead of parallel which I do think would have been better but I ran low on tubing. When I get some more I hope to try the radiators in parallel and compare the results. I managed to keep the amount of copper to a minimum, less than a foot, so fingers crossed on that score.

 

[281]

I used a parallel configuration for four radiators (I would recommend only new units). Here is a photo of the inlet/outlet manifolds I built:[attachment=0:3r1aybje]CIMG2607.JPG[/attachment:3r1aybje].