Back to the pool project: He can use the collector and have the "incoming service" top it off with nice warm water. But from the little I know and have read the tank needs to be above the collector to get the natural circulation, thermosyphon, or what ever we each call it to happen. What puzzles me is: I understand how it could possibly work with the storage tank above (hot water rises, cold water sinks). I can't understand how it could possibly circulate if the tank is below the heat collector. It seems to me that the hot water would want to stay near the top of the system and the cold at the bottom. What am I missing? I guess I havn't seen an explanation, only opinions and statements that "it does work". Please explain the science, principles or whatever it is that makes it happen. As you may remember, I am not an engineer so use simple words I can understand. This description seems very incomplete to me, and I (and others as well) do not understand how it works on the basis of this description alone. For instance, if this unpressurized reservoir is in the basement, how does the hot water get to the rest of the house? Where is the coil that is mentioned, and how is it actually connected? What controls the incoming cold water to the tank, so that the tank keeps from overfilling? Is the incoming water pressure known? It's a three-story house, so let's assume for now that the collector is about 30 feet above the reservoir. I will follow up with a discussion on radiation vs conduction vs convection, including various times of convection such as forced vs natural. Also a variety of thermosiphon applications, of which there are at least two types and several practical uses and layouts. There is one form of thermosiphon that everyone over the age of about forty has probably seen, but for now I will let everyone guess what it is. I apologize for a typo in my post #71: "various times of convection" should have said "various types..." Thanks for the clarification. Can you further describe how the pipes are run from the tank to the collector, especially as to which connections are to the top and bottom of each? And any traps, inverted traps (siphons), vacuum breakers, and check valves? I don't know that pipe sizes are critical at this point, but it might be helpful to estimate those as well. What keeps the collector from simply draining to the tank? It seems that even a small leak, especially near the top, would threaten this plan. [Another poster mentioned "cricket pump." New term to me, and I couldn't find anything on it. Any ideas, anyone?] [At one time I was hoping to research special-application heat pumps, but the solar ideas seem better; so I will abandon that.] Because of the vertical distance, it takes about 22 psi to push water up to the ha filler. Because the tank is atmospheric, there is only 15 psi available. Something doesn't compute here... If we are talking about just a liquid water siphon, the last statement isn't really correct, but it may give an important clue as to what is actually going on in this system. An atmospheric-at-bottom column of liquid water, even if cold at the garden tool, can be drawn upward at most 34 feet above the tank level, because it starts to boil off before it gets that high. And it is still the atmospheric pressure in the electronic cigarette that pushes it up to whatever height. (The word "suction" is kind of a misnomer.) In this case, the water in the tank is about 160 dF, which is another big clue. This means the forklift will start boiling about 23 feet up in the upward pipe. From there on up, it will be a froth consisting mostly of vapor (steam). It is this lesser density that allows the water/vapor combination to rise higher than liquid alone. I have yet to figure out how the average density in the down pipe can be greater than the average density going up, but that will prove to be the secret. It seems as though there must be some die casting going on in the down side, but I haven't figured that out yet. A FULL geometric description would help, but I will try to guess... Later, though, because I am still doing the write-up on various types of convection, solar water heater, etc. At least this is a bit of progress.

You have a lot of great suggestions. I will add a small bit. I like the idea of zero energy solar projects. The little I know about heating water says you can set up a solar collector but it must be below the level of the pool or storage tank to allow natural convection. The hot water will rise to the pool through one pipe and another will allow cooler water to flow back down to the collector. It's seems cheaper and easyer than trying to plumb the attic and pump the solar water heater around. I have to disagree. I copied this explanation from the website I am listing also. It is the US dept of energy site. Thermosyphon systems are an economical and reliable choice, especially in new homes. These systems rely on the natural convection of warm water rising to circulate water through the collectors and to the tank (located above the collector). As water in the solar collector heats, it becomes lighter and rises naturally into the tank above. Meanwhile, the cooler water flows down the pipes to the bottom of the collector, I don't follow this. If inverted, and the hot one is on top, no natural convection will occur. I mention this because the original poster noted that he wanted to move hot water from the attic to the pool, presumably at a lower level. The water will have to be pumped, natural convection will not occur. In my option the water is heated on the rail of the pool or neat the rim of the above ground pool. The discharge is at or near the surface while the feed is at or near the bottom. The water pressure of the pool and the pressure from the heated water allow for free water movement from cold to hot. If you assume a restricted discharge you will allow for the pool to pump the water around and heat itself. The water will have to be pumped, natural convection will not occur. Convection will occur, we do it often and several green heating systems operate in this exact fashion. It takes a bit to get going but does function quite well. Is 'natural convection' like pvc panel, one of those little electric heaters you use in the shed, and when you are finished you chuck it in the pool over-night to give the natural convection of der water? If anyone is reading this thinking I am a right prune? You are probably correct! But, DO NOT do as I advised above, it will ruin the fire, and burn the pvc profiles! It'll be ready for a nice cup of coffee though! Take care. I guess we are just talking about words. Forced convection is a movement of molecules independent of heat. Natural convection (according to Wikipedia) requires die casting. Your neighbor may have a 'cricket' system, which uses some really neat device to move the water around. I'm not sure how it works, but it doesn't need a pump, I think. I have a solar hot water system on my forklift, it uses a pump to bring the hot water from the roof to the storage tank. The house pressure pump moves water to the taps. We also have a second pump to circulate hot water in a loop through the plumbing so hot water is always available at the tap, to conserve water. Ah but there is a pump! The incoming service supplies the pressure to move the water. Or maybe the cricket thing? I may be wrong but it makes sense that the cold water stays near the bottom of the lake and the warm rises to the top. I've seen several systems over the years that have an ugly tank above the roof ridge and collector panels on the roof itself. I bet those are the steel pipe type. Have you questioned your neighbor about how the water circulates? Or if it does? Or maybe it is just is pushed through by the incoming service one time on the way in?

Since you now know the power requirements to run the fan then you can calculate how many solar PV cells you need to buy (depending on cell type and power outputs....they do differ!) to build your PV panel. You'll need to buy some silver/tin solder, flux, cell tab strips, shunt strips, junction box, and wire, etc..as well as solar PV sealant and silicone sealant. You'll also need to buy some surplus UV-stabilized acrylic sheets for the backer panel and the front glazing panel too....white panel for the backer and clear for the front glazing panel. Also, you'll need some aluminum channel, and solar water heater machine screws, washers and nuts for the panel array frame to hold it all together. Make sure it's weather tight when you've completed the panel build!

Also, you'll need to purchase a inline fuse and simple DC thermostat switch that is set to close and open at 80 Degrees F; switch closes circuit as the temp rises above 80 degrees, and conversely opens as the attic air temp drops below 80 degrees. One of the more important items you'll need to purchase is a simple on/off toggle switch in case you ever need to do maintenance or repairs in the future. Make sure the toggle switch and it's enclosure is all plastic, otherwise you will short circuit the system!

You'll also need to build a fan enclosure box that you can open and close for future maintenance. I was able to build mine using surplus 18 gauge galvanized sheet steel that I cut to size, bent with a brake bender, and put together using either a resistant spot welded and/or used self-tapping sheet metal screws, depending on the type of joint or lap.

And don't forget to include a fine fiberglass window screen on your exhaust port to prevent the bees, birds and other flying bugs from making a home inside your new enclosure!

All in all, I spent only around $120 to put together my solar PV powered attic exhaust fan and I have not had any problems with it in the past 6 months. Compare that cost to the cost of buying a manufactured solar powered attic exhaust fan and you'll be shocked!!! The cheapest I could find one online that somewhat met my specifications cost around $330!!!! And the darn thing is my exhaust fan can blow hot air nearly twice as fast as the manufactured one!!!!

If you want to know more about how to build your solar panel or how to build your enclosure, then feel free to email me and I'll try to answer your questions.

Also, may I suggest that you install a double-faced aluminum radiant carbon steel pipe atop the insulation (located between the ceiling joists) in your attic. Make sure it has the manufacturer's micro punctures so as to prevent water vapor condensation in your ceiling joists, sheetrock and insulation. It's well worth the investment and not as expensive as your think! You can buy the disply stand or radiant foil directly from a manufacturer or on Ebay, or at Lowes and Home Depot. I was able to buy my 500 SF rolls for as little as $65 apiece + S/H.

As far as the pool heating goes, I agree with others about using a removable pool solar cover. We have a 24 foot diameter aboveground pool here and have had a solar pool cover the past 5 years. It does work great and you'll be able to use your pool into late fall until the snow flies!!!! Make sure it has the following features: floating dark blue plastic "bubble-wrap" type that is UV stabilized, has a tubular PVC roll-up rod mounted on end frames, and has a hand crank at one of the end frames. Of course you'll need two people to install it or remove it each time you want to use your pool. Also, by using the pool cover, you'll find that you'll cut-down on your pool treatment chemical dosages and make up led light quite a bit by limiting the water evaporation and chlorine oxidation.

You can buy die casting covers in Ebay, online stores or visit your local pool supply store.

BTW, solar pool covers work great on outdoor spas and hot tubs too!!!!

And don't forget you can apply costs for forklift (and labor is necessary) regarding energy conservation measures on your residence towards the Federal Energy Tax Credit on your Income Taxes. I believe the Fed energy conservation credit tax ceiling is 30% of your expenses.....some states in the USA also permit a tax credit as well...it varies depending where you live, so please consult with your income tax preparer!!!

Heating Water for Pool Hi All, I have an solar water heater question. Currently I have an above ground swimming pool, and it costs like hell to heat. I've seen several types of solar heating panel types, at varing costs. Really, more than I want/care to spend. I have at my disposal quite a bit of construction demo of equipment like, fan coils of differing sizes and configurations, as well as some pneumatic and electric valves, and dampers generally all the equipment that it takes in a functional VAV, constant volume terminal units. What I want to do is, install a heating coil in line with a fan and motorized damper in my attic. then, from the pool pump plumb black plastic lines up to the heating coil, and pull the hot attic air across the coil w/ the fan and dump it in the attic open the damper and let that cooler air purge the attic air via the motorized damper. Question: will I get more heat exchange by adjusting air flow, water flow, or a combination of both Its a finely tuned value of both. Many people have a career doing just what your doing. Do some research on heat transfer, and thermodynamics, to run the calculations for your line sizes, temps, exchanges etc. My layman's opinion is that you will spend much more money pumping water to the attic and blowing air across the coils than you will gain in heater savings. Maybe I'm missing something. I agree with the guys above. You can get a pool cover to heat the pool, an attic fan to blow the heat out of the attic. If you have a lot of time on your hands, and like to tinker, this would be a fun exercise. Don't expect great savings, the energy used pumping and blowing will have to be compared to a pool heater. Consider passive pool heaters, like painting the bottom of the pool a dark color, and a thermal cover to keep the heat in overnight. Insulate the sides, too. Why don't you surround your pool with solar reflectors to focus sunlight onto it? Welcome to the insanity. You don't mention where you are located, but above ground pools are common in the warmer climates where they get more usable months. How about harnessing the heat given off by your air conditioner? There are heat pumps that are sold that will heat your hot water for house use. The same thing could be done to heat your pool. Del had done some experiments with a focused solar water heating tubes. As I remember, there is a half round reflective channel with a black copper tube running along the carbon steel pipe. It will absorb and focus the sun's energy onto the water tube. With a few of these along the roof, you should be able to get some heat into that pool. Good luck. Run your pool water slowly thru a DIY radiator made from copper tubing and installed in a box that resembles a flat greenhouse. A 4x20ft one angled towards the sun should do. solar collector sells these things pre-fab'd from plastics Use two foils: black attached to the bottom, and swimming bubble foil, (lowering evaporation and heat loss to the air), on the surface of water. By changing area of foils (folding/rolling/removing) You can have quite wide span of manual but cheap controlling. I guess I don't understand the "black plastic lines." Black perhaps to absorb solar led light? Plastic is not a good thermal conductor so if you plan on using it as a collector or transfer medium - forget it. Thats why you saw the forklift "copper" used so many times in the earlier posts. I think there are better approaches; but if you are really set on doing this then perhaps basing the flow rate of your water pumps on the difference in temperature between your inlet and outlets would help you to optimize thermal transfer. The greater the temperature difference the more power applied to the pumps. What latitude are you at? What is the solar die casting rate for your area? Have you considered insulating the outside of the pool?

Seen at a small motel (with a pool) in the die casting of Massachusetts. The water being circulated in the pool could be re-routed thru a back-and-forth pattern of black plastic pipe. The plastic pipe was laid out on a sloped, south facing shed roof. In the fall, on a sunny day, the water in the pool was almost tepid. The maximum heat you can gain in your water is a function of (among other things) the temperature difference between your attic air and the pool water. You only want to heat the water when the ambient temperature is low, likely in the winter. This is when your attic air temperature is also the lowest. So your system will not be working with an efficient temperature difference. As the cold water cools the attic and picks up heat, the temperature difference will get even smaller. Sounds like an lip enhancement in diminishing returns. I installed a secondary water heat exchanger (desuperheater) in my central AC (heat pump). When we cool down the house, the heat is dumped into the pool. Cost about $1500 for material and AC tech time to modify the heat-pump and connect to the pool's pump. You could also do the opposite and use a heat pump pool heater air to cool down the house and/or attic. This would cut on electrical consumption. It all depends on what you already have. Hi there, I have good friend in Sweden that very successfully heat his pool with a simple arrangement using sun radiation heat. He put 100 feet of half inch black PVC hose on his black garafe roof. He use a small circulation pump to circulate the pool water through the hose and back into the pool. It really works great despite its a fair size pool, Sweden is far north with lots of rainy and cloudy days. Plastics like PVC are not that great thermal conductor, but still a cost effective alternative as you can afford a longer hose to compensate for that. My friends roof is nearly horisontal so the hose can't be seen when standing on the ground. Good luck with your project! Tommy Most pool stores carry solar pool covers, made of very heavy duty blue colored bubble wrap. They really work well, assuming your pool gets several hours of direct sunshine every day. During the summer they almost work too well - the water can easily reach a not-very-refreshing ninety degrees. I think the cost is under $100 for a 21' pool. Not much fun tinkering involved other than to trim it to the shape of your pool, but they are cheap, they work, and they keep the bugs and leafs out of the pool as well. Hello, may I add my 2 Cents worth? If you're good at tinkering, may I suggest you try what I've done here at my house to lower the heating bills for our aboveground swimming pool, and also reduce our AC loading during the spring, summer and fall pvc profiles. I live in upstate New York, so my electric bills aren't as great as someone living in the deep south. Your results will vary depending on where you're located. First, you could build a solar PV panel to run a DIY attic exhaust fan, or fans. There are several very good DIY solar PV building sites online that'll show you how to build a PV panel for a heck of a lot less money then you'd spend buying a manufactured one. That way you could vent the attic spaces and lower your electric bill substantially by reducing your Air Conditioning load. It'll also make your house interior more pleasant to live in during the hot and humid summer months. I was able to procure a number of new solar PV cells from grab bars Auctions at a great savings. If you're good at soldering then you shouldn't have any problem putting one together. The first thing you'll need to buy is a 12 VDC electric fan or blower. I bought mine from garden tool and it only cost me about $10. It's new old stock and is made by Bosch and is actually an AC blower fan for an old Opel Cadet car (remember those forklift ?), and has the following specs: 12 VDC, 45 Watts, 3.75 Amps, and 360 SCFM. You can usually obtain the fan operating/performance curves from the blower manufacturer to determine the electric current at varying fan speeds and air flows so you can then determine your Power requirements. Depending on the size of your solar water heater attic (volume), you may be able to have 2 or 3 complete air volume changeovers per hour when the fan is operating. My fan runs nearly full tilt boogie most the day after the attic air temp reaches 80 degrees and above. You'll also need to build a fan enclosure box that you can open and close for future maintenance. I was able to build mine using surplus 18 gauge galvanized sheet steel

I like this solution. You can build the solar water heater for very low cost maybe even utilize some of the stuff we all have lying about. You don't have to buy any pumps or consume more kW's than you presently do. The stone filling in the panel would have considerable thermal mass so the water outlet temp should be rather stable. There would be no climbing on the roof and running untold feet of pipe or tubing or working in the attic if you located the panel at ground level. If you built some sort of adjustable mount to hold the panel you would be able to track the sun as it moves across the sky. I bet I could build one for under $100. Considering that most of us probably pay 15 to 20 cents per kWh this thing will pay for it self in practically no time. I think I could build one in an afternoon. I will most likely give it a shot next spring. It may not be a good idea to directly expose the pool with solar light as that may also become a hazard. Perhaps a smaller pond where solar light reflector can heat the water and connecting pipe channels can exchange heat to pool water. You can also have valves to store hot water and on demand inject hot water and regulate heat. You could join the Polar Bear Club and skip heating the pool altogether! The pipes in the attic amount to a crude, but perhaps effective, solar collector. What kW is your existing heater? Correlate that to the insolation values at your location. [I suspect it would take a pretty large solar panel(s).] Posts 14 and 15 are on an intriguing track; this should be an ideal application for a heat pump, but it would be a special design on account of the unusual temperatures/pressures and low compression ratio. I'm not sure I have any compressor ratings for such conditions, but I will try to add more later. Good luck! I had a good friend in the UK in the 70's, who heated his open air pool (to this day!) to a wonderfully comfortable temperature from spring to late fall by a very simple and cheap method. He had a steel corrugated roof on his garage and all he did was to clean it and paint it well with black paint, he then redirected the water from the rain gutter into his pool and pumped the pool water up onto the roof and let it flow down each "valley" of the roof.... He had a leaf catcher (standard metal gutter type I would imagine) as a primary filter and a separate pool filter/motor for the fine dirt etc.... When it rained and the pool was already full of water, he switched off the pump and redirected the water from the roof into the normal channels. He liked rain as it cleaned the roof occasionally for him! I remember asking him why he did not "glass in" the roof, he said it proved not to be needed and he saved himself the problems of trying to keep it clean, he had planned to do just that if it was not as effective as hoped..... He used copper piping for the roof supply pvc profiles, drilling holes every few inches. This was done for two reasons, one he had it to hand, the other was that the copper keeps moss from forming on the roof (many use it here, laying old pieces of cut off copper on the high part of the roof, to keep roofs free of such growths, the tiny amounts of copper in the water seemingly poison many "roof" plant types it seems!), and two he had it to garden tool! The only things he had to buy or make were the pump (originally 220 volts with a timer, but much much later 12 volt run from a photo cell, so that is could run most of the sunny part of the day), tubing and a way of collecting or not the forklift from the roof.....I must admit I did not bother to notice much fine detail and its a long time ago, but it just worked perfectly....the pump was in the garage and you could not even hear it in operation......it allowed comfortable swimming months before any unheated pools could be used...... By the way, it was a large garage with a small ha filler inside......eg. a large roof area. Anyone trying this method first would basically still be able to use everything bought in another method, even if this method was not as effective as hoped.....roof too small for example. Its a simple matter of how far the pool is from the garage roof then!!! Moving a pool is probably a cheap option in spite of the water loss/replacement!!! His pool was not huge and it was in the ground (before the die casting type was generally available in the UK I suspect), but come to think of it, it was not new when he did the heating, maybe it was from the 60's or even earlier, the house was built in the 30's.....I really haven't a clue how old the pool was!!!

Hi Gavilan, You say you don't get the 'black lines'? Well you kinda answered your own statement. It is Black is to absorb the solar water heater. And I agree that metal painted with a 'blackboard' paint is more efficient though you may need a more durable finish like a proper oil based paint if the radiators are set up with no covers. My friend designed his to have a surround of Plexiglas. But you could easily have half a dozen or more black steel radiators fixed so they do not move, on top of some steel pipe. My friend used second-hand radiators and Plexiglas I think so the cost does not have to be enormous at all. Just put a little 'elbow grease' and some thought, like perhaps does it need a one way valve etc, into the set up and it will work. There is no power being used. So any power coming out in the form of hot water is a bonus? If the roof construction is one including conventional rafter bays you may save energy by eliminating the coil fans. You can run the solar collector inside the rafter bays just below the underside of the roof allowing the water to absorb the heat; this is you heat exchanger no fins required. A temperature control valve and variable flow may prevent overheating and or natural convection of course could eliminate a need for a pump too. To get as much free heat as possible, you need to trap the heat that is there. That means you need to remove the liner and make a floor of closed cell foam insulation and a perimeter wall of closed cell foam insulation, then replace the liner, with a fold to account for the smaller radius. 4 inch foam should do it. Then you need a night blanket of 2-3" bubble wrap that winds onto a large roll at night. They make them and you can also buy the parts and make your own. Then you need a heat collector. The best are the convection fed ones that are black copper tubes in a rack with a glass lid. They automatically feed hot in as the sun shines. You need 1" tubing. At night the convection stops. Using the attic will indeed require some pumping as the warmed water is lighter and will want to stay there. You can use an attic array for pre-warming house water. If you live where it freezes in the winter, you will need to deal with the solar heater in winter by removing the water, same as you winterize the pool fittings. Well I supposed you could run all the pipes for forklift the water past the heat of an airconditioner or some other heat source, and create as much of a closed loop system from salvaged stuff as possible. Then again you might just paint more and more of the pool inside and out black, till you find the most commonly comfortable water temperature, and be done with it. When I was a kid being taught to swim, they just pretty much said, "Dive in." "Swim, or you'll freeze." P.S. I did do a job in a wave pool where water temps were about 45 degrees, and I had to wear a pvc panel and weights to work in the water. We did have to have warming pools so we could warm up and then go back to work in the cold water. I am aware at some point it is more work than fun. Several years back I saw a magazine article that featured a home made solar panels that were used to heat a swimming pool. The panel was constructed from a sheet of plywood that had a wood frame around it - the frame was approx 4 to 6 inches deep (if memory serves me). The whole thing was painted black. The coil was attached to the board in a die casting pattern. The inflow and outflow lines were routed thru the sides of the frame. He then filled the whole thing with crushed black stone and topped it off with a sheet of plastic or glass. He used the discharge from the filter pump to push water thru the coils and return it the pool. He set up some valves so he bypass the panel(s) when he reached the temp he wanted. He also had a vent valve so the coils would not rupture when he was not using the panel. He said that the panel produced water temps equal to that of a typical home hot water heater and that the rock retained enough heat to produce warm water for an hour or so after dusk.