Sunday, May 24, 2009

Solar Water Heater Prototype

Well, it has been a while, hasn't it? Too much work and house stuff have kept me from doing very much for the last few months. This project is a bit of a change since it doesn't actually involve any Arduinos or fancy microcontroller web stuff - just some good old-fashioned basic carpentry and plumbing! No fancy 3-D drawings or source code or nothing. I just eye-balled everything for this project and built it from scraps on the cheap.

Those one or two who have ever read this blog, will remember that all this started with my freezing cold pool and the need to find a cost-efficient way to raise the water temp a bit. Having worked out most of the Arduino software control issues I need to be concerned with, and with the weather being nice, I have built a small prototype of a solar water heater just to check out the heater characteristics and give me some ideas of just how big the final unit will need to be.

I decided to build this with CPVC (Chlorinated Poly Vinyl Chloride) tubing, which is cheap and amazingly easy to work with. First I built a collector element our of CPVC:

This is about 2 feet square and is about 10 feet or so of tubing. It really does go together amazingly fast. It probably took me all of an hour to get this cut and assembled. The glue is pretty foul, though! Next time I'll wear gloves.

This is the collector element installed into it's box:

From there, the collector & box were painted matt black and then got a Plexiglas cover:

Here it is all set up:

The water is circulated via a small submersible pump I bought off of eBay (click here for description). It actually moves a pretty good volume of water - it's rated at 200 gallons per hour. It still feels odd plugging in something underwater!!

So, does it work??

For a very small prototype, it does work quite well. When I filled up the collector with water and let it sit in the sun with no circulation, it heated the litre or so of water in the tubes up to 49°C (120°F) in half an hour. The water was too hot to put my hand into!

With the circulating pump running, it heated 14 litres of water from 18°C (65°F) to 29°C (85°F) in 90 minutes. This was in late afternoon sun (between 5PM and 6:30 PM) so that is probably on the low end of its performance. I'm going to do more testing tomorrow in full sun earlier in the day and see just how hot it will go. I will also have to do some Googling to find the formulae that say how many calories or energy this is and so on.

Presumably from this I can make some determination about how this would scale up to larger sizes and if a reasonable sized rig (i.e., one that is not too big to build or install - probably 10 times the size of this unit) would have any appreciable impact on the temperature of the pool, which is where this all started!

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