thermosyphon

[dylan Biofuels Forum Newbie Find all posts View Profile Close dylan]

Hi all .
I was wondering if anyone out there has had much to do with thermosyphons. I've just bought a small spar and am toying with the idea of using a thermosyphon method of heating the water. Its in a perfect position for a roof mounted type of system. The sort of thing i was thinking of is using the sun to circulate the water up out of the spar onto the roof and back to the spar using black small diameter pipe without having to use the pump .

I have the basic idea in my head but have come to a dead end. I've tried the web but all i can find is pump powered units. Surely the hot water rising principal can be applyed here with a check valve thrown in somewhere ?

If anyone has any ideas or leads i'll be happy to hear them.
happy new year . Dylan .

[G.A.Pster Biofuels Forum Newbie Find all posts View Profile Close G.A.Pster]

Re: thermosyphon

I have no idea how you’d go about it but it sounds like a good idea.

I’d try making a miniature prototype for testing before you go to the trouble of making a full sized system.

[Peda Senior Member Find all posts View Profile Close Peda]

Re: thermosyphon

Dylan hot water rises and cold water sinks, so, you would have to have the black pipe some distance below the spa for this effect to be usefull in heating. If you just have the black pipe on the roof above the spa without a pump to circulate it, the water will certainly get hot in the pipe but will stay up there. There are plenty of swimming pools heated this way but they all use a pump to get the water up onto the roof and back to the pool.
Solar hot water systems use thermosyphon and if you look how they are arranged you will see that the tank is always above the solar panels so any cold water will settle into the solar panels to be heated and rise into the tank.
Hope this helps
Peter

[dillyman Senior Member Find all posts View Profile Close dillyman]

Re: thermosyphon

Hi Peda,

A solution ,or, though not perhaps a very practical one would be to put the spa on the roof. Lateral thinking eh. It would get some great publicity.

Rgds

Dillyman

[Jacka Senior Member Find all posts View Profile Close Jacka]

Re: thermosyphon

Go to your local newsagent and buy a copy of Grass Roots, Dec/Jan 06/07 Edition 178. On page 54 and 55 is exactly what your looking for.

[Captain Echidna Senior Member Find all posts View Profile Close Captain Echidna]

Re: thermosyphon

Hi Peda,

A solution ,or, though not perhaps a very practical one would be to put the spa on the roof. Lateral thinking eh. It would get some great publicity.

Rgds

Dillyman

I dont know what I find more disturbing, the fact you suggested this, or the fact it was my first thoughts also.

I guess realistically it wont need a heap of pump power to move the water, so long as it can siphon down.

[Fat Man Junior Member Find all posts View Profile Close Fat Man]

Re: thermosyphon

Hi All

Here is a few attachments that anyone that is interested in SHW may find useful

Cheers
Fat Man

[Fat Man Junior Member Find all posts View Profile Close Fat Man]

Re: thermosyphon

Here is 2 more, I couldn't fit them all in the one post

Cheers
Fat Man

[Guest Close David]

Re: thermosyphon

I am in the process of collecting some components to test a solar system for my swimming pool. It will be a bit different to most systems but I think will also be a lot cheaper and easier to build.

My idea is to get a length of black builders plastic and support it on some frames so it is held open like a tube or tunnel. At one end will be a 12V fan ( although you could use a 240V one as long as you protected it from the weather) and at the other end will be a couple of car radiators I have aquired from people that have replaced them.

The idea will be the fan will blow air through the length of black plastic which will be heated up as it travels through and will then be blown through the radiator which will be plumbed into the pool pump to circulate the water through it.

The black plastic is far cheaper than the traditional black plastic piping that is used in solar setups and going on a 4m width with unlimited length off the roll( up to 50M anyway) a very large surface area can be set up for the best heating power. The radiators I have were leaky in the car but I have patched them up with some fiberglass resin which I think will hold fine given the minimal pressure they will have to endure unlike in a car. any leaks won't be worth worrying about anyway.

I am going to try tapping off from the return to the pool from the pump but I may also use a smaller pump so I can run it independent of the main pump. I don't think the flow required will be very great and the slower the water passes through the radiators to a point, the better anyway.

I think Dylan in the end the simplest and cheapest thing for you to do would be to use a pump but I would also reccomend you install a " solar controller" in the system. These things have a couple of temp sensors for the heated water and the pool or spa. If the water in the spa should be warmer than the water the solar heater is producing, the controller will switch the pump off so the heater dosent act like a radiator and actually cool what you are trying to heat. They will also cycle so if the heat from the solar isn't enough to heat the pool continuously, it will give it time to heat up and then pump that water through and stop to heat the next batch.

When I first became aware of this bio thing I was in the process of building a burner that would run on WVO to heat my pool. I am now running veg fueled car but the pool heater has taken bit of a back seat but I am planning on developing it more over the next couple of months.

My ultimate DIY project would be a complete WVO fueled co gen system. I would like to use a small diesel engine from a car most likely and power a generator to supply electricity to heat my home and Pool. The pool could be used as a giant heatsink so the generator could be run through the day and the heat stored to be used to warm the house at night. An electric pool heater could be powered by the generator and used to supply heat additional to what came from the engine coolant and exhaust.

Anyone know where I can get an old running diesel engine for next to nothing?

[Captain Echidna Senior Member Find all posts View Profile Close Captain Echidna]

Re: thermosyphon

I think I read somewhere diesels like operating at about %75 of their full load. For a house system you would want to keep it at full load. If you had a 50KW engine this would mean it should be putting out about 38KW. Either make sure you have a big pool, or probably better of to use a small diesel engine, say an old lighting plant or diesel generator would be ideal.

And if you find two let me know..........

[Guest Close David]

Re: thermosyphon

This is a good point you make Chris and the 75% load factor I have heard of too. I Believe I heard it stated as being the max power an internal combustion engine should not exceed for maximum longevity.

I always wondered what exactly is 75% power? Certainly in the old days one could take a stock car engine and add a significant amount of power just by changing a carburettor and putting on a free flowing exhaust. Would the 75% power level then be what the engine was capeable of after modification or when it was stock bearing in mind none of the engine internals were touched?

Anyway, your point is still valid on a stationary diesel application in consideration of the thing fouling and glazing the bores etc. especially if it were to be run on WVO. You would have the space to set up a heat exchange system to get the WVO temp to anything you wanted it to be though!

Thinking about your point, if the electricty generation was not a prime factor, one could just run the engine for a short time at a good load to produce the heat required. One could use a battery bank to store the generated power and utilise that with an inverter system but even in my imagination my pet project has budget constraints and a battery system just adds a whole 'nuther level of complexity and expense to something that would already be pushing the limits of justification for a big "toy" which is all it would be living in surburbia rather than somewhere " off grid" such a setup would in fact be an extremely justifyable thing to do.

I have read of people using the VW golf or " rabbit" engines in such co-gen systems and they run them at the relatively slow speed of 1800RPM and seemingly well under 75% load. Perhaps there is a point where they will run long term at less than ideal power output without problem.

I do have a big pool ( 80,000L) but I can well imagine it wouldn't take long to get it quite hot fairly quickly if one were to dump say 20KW of heat into the thing for any amount of time.

Until I find an engine (or 2) all this is just brain food thinking about how to set up and design such a system so I'll keep enjoying it for what it is at the present time

[dylan Biofuels Forum Newbie Find all posts View Profile Close dylan]

Re: thermosyphon

Well i got hold of Grass Roots magazine . I think i can do it without having to put the spar on the roof . I could plumb into the spar's plumbing and have the water pumped up to the roof through a coil of polypipe with a gate valve to control flow and heat . Or alternatively i could put the coil lower than the spar and let the syphon effect take place ,also with a valve . This would mean i would'nt have to turn on the pump to heat the water. I'll try this first i think . Thanks guys. I'll let you know how i get on . Dylan .

[Captain Echidna Senior Member Find all posts View Profile Close Captain Echidna]

Re: thermosyphon

I would take a ballpark figure of if the throttle is at 75% of the maximum, then its operating at about 75%, if it is holding the same revs (regardless of what the revs are) if its increases its rpm, then its underloaded (which would require the throttle to be reduced to stop overreving)

Wether its 75% of power at the revs at the time, or 75% ot the total power for longevity I dummo?

I would presume using the generator for "big loads" like the washing machine, (and charge the batteries as well) and run the smaller loads from an inverter. Of course a few car alternators could also be a good way to charge batteries as well?

What no spa on the roof? I am sure of the local council would let you if you said it was energy efficient?

If you find 2 engines, I hve a 2.5KW 240V alternator sitting in the shed awaiting an engine.....

[Guest Close Marc1]

Re: thermosyphon

David, your idea to use solar heated air in stead of water is interesting, however I think you should work out first if it will be feasible.

The specific heat of air is very low compared to a very high specific heat of water, so your flow of heated air must have to be enormous. Also the heat pressure or rather the differential between heated air and water must be high to go through the car radiators. If you have chosen copper/brass old radiators they are very inefficient conductors due to the tin/lead soldering that insulates the copper fins from the brass tubes making them poor conductors. An aluminum radiator would help yet I am afraid the differential temperature you can obtain will make the system rather slow. Try to figure out dimensions and heat output before you embark in a big construction.