i am considering placing solar heater piping on my garage roof. i have some questions and would appreciate your insight/experience:
height - we have a 1.15hp pump. will it really be able to send the water up 12-15 feet to the roof? i imagine almost full power will be needed. i dont expect there will be loss of pressure at the returns because the water will gain some velocity in coming back down, right?
stagnancy - if you dont run water through the solar pipes, does the water which is sitting in there from being primed stagnate?
durability - i was shocked to see these tubing panels frequently come with 10 year plus warranties. how can black rubber that gets beat on by the sun not break down sooner??
in that same vein, i understand you can leave it on the roof for winter? wouldnt snow piling, and freeze thaw cause them to break down as well? we live in ontario, canada and can get quite harsh winters
thanks in advance for your replies
Your panels should be installed such that they have at least a slight angle to them. Not only from bottom to top, but from the lowest
corner to the highest, opposite corner. This ensures that they fill and flow correctly, for maximum heating efficiency, but also drain as completely as possible. If you're going to install yourself (or manage installers), be sure this concept is well understood and executed. Panels not sloped correctly (in both directions) will not drain properly and will not heat as well as they should. (I'll point you to the "how to" on that when you're ready.)
If sounds like your panels will be higher than the surface of your pool, and if so, the angle described above, and a special "solar valve" that will feed the panels, along with a vacuum relief valve included in the plumbing somewhere (the "non-sealing valve" Allen describes), will allow the panels to drain almost completely
each time the pump is turned off. So no, the water won't stagnate, because it will drain out after each use (typically every day).
The usual solar heater system is set up to engage and fill its panels each morning when a solar controller (computer) determines there is enough sun on the panels to add heat to your pool. The controller will start and stop the flow through the panels throughout the day based on the available heat. It might run straight through, and then stop when the pool reaches the desired temp, or it may start and stop multiple times a day if the heat availability is not steady (like on a partly cloudy day). But as long as the pump is running, the panels will stay full of water. Then when your pump is scheduled to turn off at the end of the day, the solar valve will allow all the water to drain off the roof back into the pool. The cycle repeats each day. If you keep your pump running 24/7, as some folks do, the panels will never drain, even if not being used to heat the pool.
At some point, either because it's too cold, or your swim season is over, your system should be turned off, drained one last time, and then winterized. There are a few ways to do this, but the point is you don't allow water to remain in the panels throughout the winter. My installation keeps the panel tubing well off the roof tiles. But it doesn't snow here, so I never have that kind of load on my panels. I don't actually know how that is handled in areas with a lot of snow. That would require some research, or a local installer to advise.
I expect to get at least 20 years out of my panels. I expect there might be some leaks, but repairable. My warranty is 12 years. They use UV-rated materials for the panels, so they should last at least 10 years without issue. I suppose some manufacturers skimp on materials, and might deliver a product that doesn't hold up (whether warranted or not), but a good set will last. Which is why I bought the best I could find (Heliocol). They've been around a long time, and wouldn't be if they couldn't honor their warranty. Consider that when buying the panels (or anything else), a warranty is only as good as the company offering it.
@mas985 is our resident pump expert. He can weigh in about your pump's capability. My pump is 3HP, so I can only say I know
that works (and doesn't require anywhere near full RPM to fill the panels)! But as Allen pointed out, it takes less pump and energy than you might think. Except for the initial fill, the pump only needs to overcome the pressure and the friction of the water through the panels, gravity does most of the work.
