Wednesday, July 1, 2009

Weekend Project: Solar Pool Heater

We love to swim…a lot. Our boys swim no matter what the pool temperature is. Unfortunately with Maryland weather it is mid to late June by the time the pool is comfortable for me and Mrs. BelAirLife. So to be able to start swimming sooner in the spring and later into the fall I started researching heaters. But I’m cheap. It helps to know that up front. Some people call it frugal, but I’m cheap. So early on in my research, after I got over the shock that heat pumps and gas heaters cost $3,000-5,000 (some even more) and can cost anywhere in the $200-800 per month to run them, I quickly ruled them out. Then I started researching wood heaters. Wood heaters are cool because I could get all the free junk firewood I would need to run one. But, they still have a $3,000+ price tag, have to be fed wood every few hours (because of the size of the firebox), and would constantly be pumping smoke across my back yard (the top of the smokestack is only about 5’ high). So that pretty much left solar.
I started looking at different solar heating systems and at some point decided I just had to be able to make my own solar heater that was better AND (more importantly) cheaper. So I started researching plans on the internet and I stumbled upon a plan I really liked and starting thinking of ways I could improve it. Since my pool is in ground and about 22,000 gallons I decided to double the plans and make it 4’ x 8’. Our homeowners association forbids solar panels on roof tops (stupidity and another reason I hate HOAs) so this would have to be ground based.
I started by going to Northeast Plumbing Supply in Rosedale to see if they had irrigation hose. Irrigation hose is more like a flexible PVC pipe than a garden hose and my theory was that it would be cheaper, solid black and effect better heat transfer while withstanding the higher heat condition of asphalt shingles which I planned to use as backing. Northeast had tons of tubing and in various sizes. I bought 200’ (although I only used 150’) of 5/8” tubing at about $22 per 50’ roll. The guys at Northeast (who were extremely cool and helpful) also helped me pick out the fittings and adapters I would need to both connect one end of the tube to the beginning of the next and break the tube down to a standard garden hose. The picture explains it better than I can in words and I am sorry I do not remember the names, sizes or thread patterns of all the fittings.
Then it was off to Home Depot for a sheet of 4x8 plywood, 3 2x4s, 2 contractor packs of wire clamps and screws. The bill at Home Depot was about $40-50. Thankfully I have a ton of leftover black shingles from my roof.
So once home I laid out the plywood on sawhorses, then laid out all my shingles onto the plywood but I did not attach them. Next I cut my 2x4s and framed out the plywood over the shingles. I planned on setting up panel laterally so I used a 1” drill bit to drill holes for the hose to pass through the 2x4s, one for entry on the top right and one for exit of the bottom left. The idea was to get a little help from gravity. I then fed the hose and began coiling onto the panel. I decided on two 4x4 coils to maintain a circle, that way water was never travelling directly vertical for too long. Every so often I would affix the tube with a cable clamp and screw it down through the shingle and into the plywood. To save clamps I spaced them out and used wire ties between to keep it all secure. I kept this up until my spiral was complete and then moved over to the next one, then out the exit hole.
I also decided not to make permanent changes to my pump set up which is why I used garden hose fittings. On the out I just have a garden hose that runs the water into the side of the pool. For the intake I have a section of garden hose that runs from the heater long enough to reach a jet on the side of the pool. At the end of the hose I cut it off and shoved a 1’ piece of the irrigation hose into it. I can then slide the pool jet over the irrigation hose. Then I cut off two ¼ inch pieces of garden hose to slide over the irrigation tube and act as stoppers. I can then screw the jet back onto the pool. I have very little pressure increase at my pump this way when running the panel s so I have been comfortable doing it this way. I do recommend priming the whole system (at the beginning of the season) from a spigot at the house before running it off of the pool pump.
My pump is on a timer so the panel kicks on each day with the pump. It has been extremely effective and allowed us to swim in late May and early June this year. Should also help us swim much later into the fall. By August we will have to disconnect it to keep the water from getting too warm and reconnect it again in September. When using I also recommend using a solar blanket/cover to help retain the heat at night so you don’t lose what you have created during the day.
I’ve never measured the temperature difference before and after the panel, but you can feel a significant difference. I’ve contemplated covering the panel to avoid wind loss of heat on the panel itself. Plexiglass is expensive and loses clarity too quickly in direct sun. They make UV resistant plexiglass, but it is big bucks and in case you have not caught on by now, I’m cheap. Glass, even tempered, is out of the question for me near a vinyl pool. My solution was to position the panel so it is fairly well protected from a breeze but to also get as much daily sun as possible. The panel gets direct sun starting about 10:00 a.m. through to about 4:30 p.m. most of the summer.
If you make one of these, leave a comment. I’d love to see how you make yours and what improvements you make.

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