Author Topic: CS thermosiphon  (Read 4112 times)

mikenash

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CS thermosiphon
« on: August 14, 2017, 08:38:18 AM »
Hi guys

I'd be interested in tapping into someone's experience here, as I know several of you folks use the heat from the Lister cooling water for things like heating houses, or for domestic hot water . . .

I have just poured a concrete pad and bolted down a base for my CS and genset.  It will see the base of the CS bolted down on top of the steel base about 400mm (16 inches?) above the top of the concrete pad.  The plan is to then pour the floor at a level about 100mm (4 inches) above this pad, so that the feet and lower section of the steel base are encased in the floor of the shed as a vibration-damping device.

Local Councils here don't care about a shed if it's less than 10 square metres; so I guess this one will end up being maybe 3.3 metres on a side (say ten feet-ish)

The other things that need to go into the shed (diesel tank, cooling water tank, battery bank etc etc ) will determine whether the CS sits central, off to one side, or sort of up against a wall.  I favour "central" for ease of access at this stage of planning; but we'll see

Now, every house I have ever built or modified has had a woodstove with a wetback, so I'm comfortable with thermosiphon processes . . .

I have been thinking of using a 135-litre (30-gallon-ish) copper hot water cylinder as a cooling tank for the CS; and using the "in" and "out" plumbing and the internal riser on the "in" of the hot water cylinder as they would be laid out for use with any other thermosiphon system, so that I can have a low-pressure feed of water to the hot water cylinder at about half or maybe two-thirds of a bar (think, say, seven metres or twenty feet of head)

That would mean I need to mount the cylinder so that the base of it is a little above the "top hose" point of the Lister's cooling system, so that the hot water feed pipe is level or slightly rising between the head of the CS and the base of the cylinder, but actually terminates  about 800mm (two and a half feet-ish) above that, at the open top of the riser inside the cylinder.

I'm just kicking this around as where the cylinder sits has some bearing on the shed layout, see . . . .

Basically, I'd like to be able to have a "hot tap" pipe coming off the top of the hot water cylinder once the CS has put some heat into it

If there's half a bar or so of pressure in the cylinder (no different to a radiator with, say, a ten-pound pressure cap) do you think the thermosiphon will still work OK?  It works fine under identical circumstances when the heat source is a wetback . . .

Or maybe that bit of pressure is asking for trouble with the CS's water jacket?

I'd be interested in any thoughts or experience

Thanks, Mike

AdeV

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Re: CS thermosiphon
« Reply #1 on: August 14, 2017, 10:20:13 AM »
I mocked up something similar a while back, but my copper cylinder (foam lagged) has a "heating coil" inside of it, thus the engine coolant (which may contain glycol of course, if you don't want to be faffing around draining it every night in winter) is kept completely separate to the water being heated. I didn't dare try to thermosyphon with the heating coil, I figured even if it did work, it wouldn't work well enough to avoid boiling in the head, so I used a standard Grundfos central heating pump to pump the coolant. I found that, with the tank full of cold water, it took around an hour of steady running under load to get the tank up to 50C (at which point, my thermometer runs out of scale...). As I had no further plumbing attached to the tank I couldn't then use it for anything except "ooh, aaaah" factor.

One thing I never did (which I should have done) was checked the temperature at the engine head, I have a feeling I ran it too cold for too long; when I come to play with it again, I'll probably put a small circuit in with a thermostat, so the engine can get up to full working temp before the entire tank does.

Also, based on my experiments, if you plan to run the engine for more than an hour at a time under a decent load, you'll either need more water tanks to store the heat, or some method of dumping excess heat once the storage tank is up to temperature... or you'll cook something. A UK-sized domestic HW tank (lagged) doesn't shed heat fast enough, so eventually you'd get boiling, which I suspect would be A Bad Thing.

You can see a bit of my old setup in this video: https://youtu.be/9Y5iUHfBdFQ?t=1m30s I've since moved (three times!), and the engine's not set up to run just now... but I've still got the tank, and all the plumbing etc.

Cheers,
Ade.
Cheers!
Ade.
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1x Lister CS Start-o-Matic (complete, runs)
0x Lister JP4 :( - Sold to go in a canal boat.

dieselgman

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Re: CS thermosiphon
« Reply #2 on: August 14, 2017, 11:59:46 AM »
I am not aware of any thermo-syphon problems due to pressure in the system, but the CS head gasket is not known for a very robust performance with pressure in the system. They are not built well for a pressurization of the cooling system and often have some tendencies to easily leak. Some of the modern composite head gaskets with silicone will perform better under these conditions and that option may become necessary in your proposed case.


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Hugh Conway

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Re: CS thermosiphon
« Reply #3 on: August 14, 2017, 05:00:36 PM »
@mikenash
We are using a thermosiphon set-up for our domestic hot water in winter.......this with a coil inside the wood burning stove. Circulates into a brass tank of about 115 litre capacity. That system is pressurised to about 50 psi and works fine. In a closed system, the thermosiphon is unaffected.
With the Listeroid 6/1, I used to run a thermosiphon cooling system also with a 115 liter tank. Tank is vented to atmosphere. The engine and tank were in an open shed. After 2 hours of run time at a fairly high load (around 2800 Watts gen output) the tank was still not very hot, in fact cold at the bottom half. The system was properly set up with the bottom of the tank well above the bottom outlet on the cylinder. I have now changed to an old 10 fin cast iron radiator which seems just about right for use in same circumstance.  Heats up quickly, does not boil. Thermosiphon is a very trouble-free system. I use a 50/50 anti-freeze mix as the whole set-up is exposed  to outside ambient temps and used daily in winter. It can reach down to -15*C here.
As has been said, you may have a problem with pressurising the CS cooling system due to the head gasket leaking. Some have been successful though.
Cheers,
Hugh
« Last Edit: August 14, 2017, 09:10:48 PM by Hugh Conway »
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Tom

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Re: CS thermosiphon
« Reply #4 on: August 14, 2017, 06:11:58 PM »
Our system uses a 30 gal tank with hot water being pulled off the top hose to heat the hydronic floor of our house. There are no head exchangers in the system. Once everything was balanced it works great. Most of the info on my system is on the Micro Cogen board.
Tom
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mikenash

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Re: CS thermosiphon
« Reply #5 on: August 14, 2017, 09:09:30 PM »
Thanks for the insights on that, guys.  It seems as if pressurising the CS head is potentially asking for trouble.

The smart thing for me to do is probably just to fit the cylinder, give it a wee ballcock-filled tank at the right level to keep it topped up, and leave it at atmospheric pressure.

Once I have a handle on how much - or how little - heat is generated, and the volume of cooling water required, then I can have a play with pressurising it.

Really, I was just attracted to the copper cylinder because it won't rust

I was away from site for a month or so recently and the winter frosts burst a small fitting between the gas hot-water califont and a "hot" tap.  Water began to flow through the califont which obligingly switched itself on and ran for however long it could before emptying a 9kg tank of propane . . . . there was only a small fire; but there was a substantial flood.  I can now add "replace flooring" to the to-do list

Clearly I'm going to have to consider frost-protection for the CS.  Probably simply draining the water when not in use will be easiest

Where I live we get lots of grey, crappy, winter days but no real hard frosts.  However, my new site, where the CS is, has a different climate

No-one to blame but myself for that one . . . .

Thanks for the thoughts on thermosiphons

dieselspanner

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Re: CS thermosiphon
« Reply #6 on: August 15, 2017, 08:55:43 AM »
Would it be practical to use a tank with a coil 'the other way round'?

By which I mean use an unlagged, unpressurised, copper tank as the 'radiator' and then either circulate or run the incoming cold water feed to the heating system's domestic water through the heat exchange coil to pre heat the supply.

There would still be the frost issue, antifreeze or drain down in winter conditions for the cooling water, and if you anticipated cold weather and were not planning on running the CS, a bypass with a drain down valve on the coil would protect the domestic feed.

If one went down the pre heat route the cooling system would work as per normal, and the cold water feed to the hot water tank would require no pumps etc. resulting a simple system for the sake of a couple of hours plumbing and lagging.

Not that any of this is my intent, well, not at the moment.............

Cheers Stef



Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

mikenash

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Re: CS thermosiphon
« Reply #7 on: August 15, 2017, 09:58:21 AM »
Would it be practical to use a tank with a coil 'the other way round'?

By which I mean use an unlagged, unpressurised, copper tank as the 'radiator' and then either circulate or run the incoming cold water feed to the heating system's domestic water through the heat exchange coil to pre heat the supply.

There would still be the frost issue, antifreeze or drain down in winter conditions for the cooling water, and if you anticipated cold weather and were not planning on running the CS, a bypass with a drain down valve on the coil would protect the domestic feed.

If one went down the pre heat route the cooling system would work as per normal, and the cold water feed to the hot water tank would require no pumps etc. resulting a simple system for the sake of a couple of hours plumbing and lagging.

Not that any of this is my intent, well, not at the moment.............

Cheers Stef

And, of course, as soon as you build anything like this which is effectively a heat-exchanger, you can run 50% antifreeze I guess, too

Good thinking, cheers

ronmar

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Re: CS thermosiphon
« Reply #8 on: August 20, 2017, 05:29:46 PM »
I don't use a tank at all on the primary loop.  I have my 6/1 thermosiphon thru a small(5" X 12") 10 plate brazed flat plate heat exchanger with 1" ports.   Because of the now low mass in the cooling side of the thermosiphon loop I did have to mount the heat exchanger about 30" above the 6/1 cylinder head but it functions well at all loads.

The primary loop has a 195F thermostat at the cylinder head outlet so the engine rises to and maintains op temp quickly.  The primary loop is unpressurized with a small expansion tank at the top of the system near the heatex. The primary loop has propolene AF(non toxic) and the secondary loop is dom water circulated by a pump to a domestic water tank. 

I put a 120F outboard motor thermostat on the outlet of the heatex secondary to modulate the flow of domestic water so the heatex outputs 120F water. The heatex is rated to 400 PSI so I can run domestic water pressure on the secondary. The water circulates into the tank from the top down and the return to the heatex is from the bottom of the tank.  Once the tank is hot, and hot water starts flowing out of the bottom port, I dissipate the heat from the tank return to the heatex thru a fan-coil unit.  Because of the modular nature of the assembly, I can place the fan-coil unit inside the house near the tank if I want the heat there, or out in the generator shed to dissipate the heat outside...     
PS 6/1 - ST-5.

starfire

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Re: CS thermosiphon
« Reply #9 on: August 24, 2017, 12:59:09 PM »
I have an old wall type hot water school radiator heater in my lounge, this is fed from the cooling water. The engine is 3 to 4 meters away giving an 8 meter circuit.  I didnt think it would work, but work it does very well. If you think in terms of the return to the engine, any circuitous path seems ok. The top engine outlet must rise higher than the engine to initiate the water movement. I have a small water cylinder near the engine the bottom level with the cylinder head. The water rises approx 700 mm into the top of the tank, the tank is open to the air and the water level must be above the pipe.
The bottom outlet from this cylinder or tank then diverts to the house radiator, then returns to the engine bottom intake.
When the engine warms, the water has to rise, and in doing so sucks water in from the house radiator. The house radiator is replenished by the slightly cooler water at the bottom of the first tank. This small tank and pipes are  lagged to heat faster, all pipe is 2 inch plastic PVC waste pipe as the water never exceeds around 70/80 degrees C. The house radiator is roughly at the same level as  the engine.
Its great for taking off the winter chill. My experiments with collecting exhaust heat were a failure, there seems to be little heat here to grab unless the engine is working hard for long periods.
Really, this headgasket thing is nonsense, in my case, the pressure is slightly above atmo.... the height of  a 700mm column of water . The only minor problem I had was initially purging the air, as the interconnecting pipes to and from were underground to insulate them with dips and hollows. A blast of water from the hose at the start fixed this. There will be no circulation with air pockets.
Basically, if there is an unrestricted  head of water above the engine cylinder head, then a thermo syphon will occur.

dieselgman

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Re: CS thermosiphon
« Reply #10 on: August 24, 2017, 01:47:53 PM »
Quote
Really, this headgasket thing is nonsense, in my case, the pressure is slightly above atmo.... the height of  a 700mm column of water .

Your water column will not result in any real pressure in the cooling system as in Original Post proposal with a closed pressurized system. Thus no problems with water leaks.  :laugh:

Your experimental details and triumphs are good to hear!

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