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Forum Index : Solar : Passive Solar Water Heater
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MacGyver Guru  Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Crew As promised, I have begun building stuff again after moving to Texas. I have all the "necessary" projects out of the way and finally begin to play once again in my back shed. First up is a passive solar water heating application, which will provide me with 30 gallons of scalding-hot water every clear day. The only exception will be days when the mercury is down in the freezing area. On those days, I'll simply drain the system and use either gas (propane) or electricity to heat water. I have built this out of every-day, common materials, which anyone can either scrounge or purchase at their local hardware or big box store. I know there will be those who will want to jump in and tell me I should have made the manifolds out of larger pipe, but I did it this way for two reasons. First off, making the manifolds as well as the heating surfaces out of all the same-size pipe (1/2 " copper), the cost of fittings is manageable. A 1" reducing Tee costs in the neighborhood of about $7 with the price of copper sky high these days as opposed to a half-inch tee, which comes in at around $1.50 or so. By the way, I used a roll of 1/2" soft copper pipe I had lying around from my plumbing days. With the price of copper at the top of the mark, scrounging is the best way to get a lot of the parts. My motto is: Use if up, Wear it out, Make it do, or Do without! Secondly, from experience, I know using all smaller pipe, the pumping action (thermo-siphoning) speed is increased if the headers are small-ish. I've done these kinds of applications before and believe me, simple is best! Murphy is always lingering around a corner of the shed and will invite himself to any and all projects. Ii used lead-free solder and zinc chloride as a flux. Map gas makes things happen faster, which is about the only short cut I took on this project. Here it is in pictures: 
The size of this collector plate was limited to that of half a sheet of galvanized roofing tin, which I had kicking about the shed. I use it as a reflector (more later). I painted the inside as well as the outside to protect the enclosure from damp weather. The two open slits are nothing more than the result of running out of scrap plywood kicking about and my unwillingness to buy another sheet of plywood just to fill in the cavity. I'm cheap; I know it. 
Next, I lined the inside of the wood box with alumim-backed foam sheet wall insulation. I had some left over from my insulating my barn this last summer. I got it at Home Despot; it's not cheap, but it's not all that expensive and is necessary to retain the meager amount of heat this small, flat-plate collector can soak up. 
Here's that piece of galvanized roofing tin again. It was cut to fit snugly inside the box, just atop the sheet foam. I designed each leg of the heating surface to align with a pair of "trough" bends in the sheet metal. I chose the shiniest side to face outward. The idea here is to reflect sunlight onto the rear surface of the pipe as well as letting it soak up direct sunlight on the front face. 
Next, I drilled both an entrance and an exit hole in the side of the wood box, which each alignes with the inlet and outlet pipe of the tubing array. The color of the pipes, connected to a manifold at each end with a copper tee and an elbow at the terminal run are painted FLAT black with high-heat stove paint. I just happened to have a can of spray paint sitting around. I chose flat, because I want to "absorbe" heat, thinking glossy paint might "reflect" sunlight. At any rate, the pipes in the picture actually look like bare copper, but I assure you, they're flat black. 
I secured the terminal loop of pipe (last run) to the metal roofing material, in order to keep things from shifting position in transit. I want each of the several (8?) black, copper loops to be in position so as to accept the maximum amount of reflected solar radiation. If the whole thing shifts or slips, I might lose that modicum of an advantage. I'm sure it would still work even if the focus it a bit out, but I just want to give it my best shot. 
Lastly, I covered the whole thing with a sheet of Lexan plastic, which I purchased at Home Despot. It was only about 10 bucks for an 8-foot sheet. I used half a sheet here. Note the clever little plastic thingy (also purchased at Home Despot) which seals up the ends of the plastic sheet. I'm sure the sheet of Lexan has those troughs and valleys to make it stronger, but without sealing the ends, air flow through our toy would remove about 97% of all the heat. We don't want that. I might add here, remember to INSULATE all your pipes both arriving as well as leaving your solar heater. If you miss ANY pipes, leaving them exposed to ambient air, all your efforts are in vain. You MUST (read that: if you don't it won't work) insulate ALL your pipes. 
Here's the finished product propped against my new fence behind my back shed. It's a simple flat-plate solar collector. By using the lower pipe as the cold inlet, in a loop with your hot-water storage vessle and the upper pipe as the outlet, this thing will "pump" itself without the need for an actual pump. Remember to have as few bends (fittings) in your piping to assure the water flows with the least amount of resistance. Too many changes in direction make it necessary to add an electric-assist pump. If you build and install this as I've outlined here, it will give you many, many years of absolutely FREE hot water. Remember to INSULATE, keep your runs short and as fitting-free as possible and DRAIN THE THING if the weather freezes! As soon as it stops freezing at night around here (April?) I'll install this and add some pictures. ALL the water piping in my house (RV) is Pex. Pex pipe will not break if it freezes (although once this year already, the hydraulic forces associated with water freezing inside a pipe (frost wedging) was enough to completely strip off all the plastic pipe under each of 12 stainless steel knives designed to clamp onto the pipe and prevent ANY movement in it whatsoever. Expanding ice creates AWESOME forces, so to be fore warned is to before armed! . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Nice build Mac. Keep us posted on how it goes. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Mac, you can fit a simple frost protection valve to the lowest point of the collectors. These start to dribble when the temperature falls to a couple of degrees above freezing. This pulls hot water back down into the collectors and positively prevents freezing. I agree that the whole thing should be drained during winter, but a frost protection valve would be a very good precaution either side of the coldest winter months. http://www.avg.net.au/~avgcom/index.php/products/category/fr ost_protection_valve http://www.allvalve.com.au/newsFPV.htm http://www.solazone.com.au/hitachi-frost-protection-valves.h tml Cheers, Tony. |
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