I'm in WA with annual rainfall about 350mm, all of which is in winter. However, I'm blessed with a dam fed by a year-round stream. I'm thinking of creating some form of heat pump, to use some of the high summer temps to get water up to tanks. Anyone with any ideas would be welcome. This is what I have in mind. I'd have a black collecting box floating on the edge of the dam. from there, it's a pretty steep slope up about 60 metres to where my rainwater tanks are. If I run a black poly pipe up the slope, I should get some evaporation going up the pipe. The pipe is exposed so the temperature should be maintained. If I bury the last 10 feet, and switch to white pipe, i will hopefully get condensation at that point. I'd need to figure out how to collect it, but that shouldn't be too hard. At this stage the water isn't for drinking, so I wouldn't need food grade tubing for collectors. Since the water I'd get would be minimal, and the stream flow is much faster, there wouldn't be an effect of increasing the salinity of the dam. Anyone got any thoughts on this? :?:
Re: Heat pump If I understand what you are suggesting, then I think the gains from this would not be worth the material or labour input. My guess is that it would be more efficient to scoop up a five gallon pail and walk it up the hill once a year. You'd be better off using wind power or, if the stream is big enough, a ram pump.
thermosiphon? Hi TonyC, I'm confused about your idea. Are you proposing to collect water in your black box by process of evaporation? If so, I agree with Dougie in that it seems like you might get some water into your tanks, but hardly enough to make it worth your while... But at first I thought you were suggesting to set up some kind of thermosiphon and it seems like that might work. Just like a passive solar hot water system. I am thinking you would take your black polypipe and tie a weight and a floast to the end so that it always stays below the surface of the pond. You would run your pipe up to your tanks and stick the end in so that it is completely submerged and then somehow fill your line with water, purgin all the air bubbles. A solar collection plate placed around the intake in the dam would heat up the water in the pipe so much that it would try to rise and force its way up the the pipe until it got to your tank, no? You might need to set up some means of circulating the water in the tanks to always make room for the hotter water though? I don't know how much head a thermosiphon could deliver, but if it worked it would definitely be the least energy intensive way of getting your water uphill! It might be totally unrealistic, I don't know. Perhaps the thermosiphon effect of hot water systems relies on the pressure of the water system it is connected to... If you have enough flow rate and head in your stream a ram pump would be the next thing I would look into, as Doug said. If not, I would probably look at a DC electric pump and a small photovoltaic panel before I tried to put up a windmill. I think they are cheaper and less hassle. You get plenty of summer sun in WA, no?
For the thermosiphon to work, the force generated would have to be greater than the acceleration of gravity (9.8m/s2) times the mass of water in the hose. It wouldn't be. The water would flow from the top 60 metres above (a very great distance) to the bottom dam and it would do so very quickly. The municipal water tanks in most Canadian towns are abound 30 or 40 metres high, and there's no way one could use a thermosiphon to go against the pressure they generate. Again, I recommend a ram pump for the stream: https://www.animatedsoftware.com/pumpglos/ram_pump.htm
gravity is so heavy a-ha! Of course you are right DOuglas. I suppose on my part it was a case of wishful thinking. We have these solar hot water tanks that are much higher above the panels, but of course they are assisted by the gravity feed from the supply tank which is much higher again... So TonyC... what is your next move?
thermosiphon I'm not convinced it couldn't work. Definitely a closed airless pipe between a high and low source would siphon all the water from the higher source. But if there were one-way valves at both ends of the pipe (allowing only uphill flow) this would not happen. The upper end would not need to be submerged either (but I think it would work better if it was) Yes the solar energy captured would not be a great amount. But I think of the number of times I've burned myself on water that's been sitting in black hose pipes in the sun, and think that the energy must be able to be used for something. What am I missing? Why can't the expansion of the water in the pipe create a pumping effect? How hot would it need to be? Boiling? Solar energy can easily directly make water that hot, given time. I think it's time for an experiment on a small scale...can I get water from a low point to a high point using only heat on the pipes and controlling the valves?
You would still have to be going against the force of gravity and the force generated would be trumped by the force of gravity. It is my understanding that thermosyphons are used for water circulation in a closed system, not for water transport. I think that you've got a great idea here. That is a really big part of design. Annidation of elements in a design means that from a human perspective, less goes to waste. There is all this solar energy trapped in the water, as you say; and it could be put to use, if the designer can only figure out how. My thoughts would be to use the pond as a thermal regulator and take advantage of the microclimate heating effect of the pond to grow plants that might otherwise not survive. I suspect that other people here could come up with a more sophisicated usage, though. The first problem is that fluids don't expand or compress very much. More accurately the expansive and compressive capacity is very minute - almost immeasurable. This is why the brakes in a car are controlled by a fluid system. When you hit the brakes in a car, the fluid in the brakeline (virtually) does not compress; and this makes the break pads sqeeze against the brake disc. Since the capacity of liquid to expand or contract is extremely small, cars today use fliud brakelines and not cables - the cables will stretch more that the fluid will compress. The apparent compression in a fliud brakeline comes from the expansion of the lines itself, not from the fluid. Were that the thermal expansion of water greater, you would then be faced with the problem of expansion and compression of the line carrying the water. Boiling is a whole other game. Then you are dealing with a gas, not a liguid. The problem is getting the water to this temperature. You might use a central receiver system in which an array of mirrors reflect sunlight onto a central tank containing water. The heat would then turn the water into steam. The problem is the energy it takes to get the water into the central receiver and the expense of the system, which realistically needs to be computer controlled. If the aim is just to transport water, then the costs in energy would be far greater than the gains.
