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Post by gadget on Feb 8, 2019 10:17:52 GMT -8
What size tubing are you running in your system? I have seen lots of reference to 1/2 copper or bigger. I have done some testing with 3/8 copper tubing 25 feet in length with good results. I'm moving about a gallon a minute and getting 10-15F rise in temperature.
Is larger tubing better or safer? less pumping loses?
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Post by coastalrocketeer on Feb 9, 2019 12:59:23 GMT -8
Smaller tube has a higher risk of flashing water to steam, with a lower amount of heat input... larger surface area in proportion to volume of water and flow rate.
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Post by gadget on Feb 9, 2019 20:45:55 GMT -8
Smaller tube has a higher risk of flashing water to steam, with a lower amount of heat input... larger surface area in proportion to volume of water and flow rate. Thanks for your input. The 3/8 copper I'm testing with is working really well. It seems to have lots of buffer room. The rocket I am using it with has low output. I'm running the line in the barrel coiled up above the riser. I'm actually having trouble with condensation dripping from the tubing, Even with the top of the barrel hitting 500F. I guess if your pump dies does it really matter what size tubing? Its going to flash either way right?
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Post by gadget on Feb 9, 2019 21:42:00 GMT -8
So I did some math on surface vs volume and got the following for type L copper tubing assuming a 10' length. All number are inches surface squares and cubed volume. 3/8 Copper type L tube Surface area 377.4 Volume 24.5 Ratio surface to volume 15.4 to 1--------------------------- 1/2 Copper type L tube Surface Area 471.8 Volume 35.2 Ratio surface to volume 13.4 to 1--------------------------- 5/8 Copper type L tube Surface Area 566.2 Volume 44.8 Ratio surface to volume 12.6 to 1--------------------------- Using these specs
This area and volume calculator And this ratio calculator
I bought some 1/2 tubing for using in my next heater. in theory, it will not be as efficient in transferring heat as the 3/8 tubing.
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Post by coastalrocketeer on Feb 10, 2019 12:01:15 GMT -8
I think the low pressures of passive thermosyphon driven systems are where the increased tube sizing becomes most critical...
Seems like you’re ok with your current burner’s heat output with 3/8’s tho, so that’s good. :-)
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Post by johnjorgensen on Feb 10, 2019 13:13:59 GMT -8
The water in my system is being pumped through a wall radiator in the barrel. I plan to find a pressure relief valve, so I know where the steam will go, just in case....
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Post by gadget on Feb 12, 2019 8:24:35 GMT -8
The water in my system is being pumped through a wall radiator in the barrel. I plan to find a pressure relief valve, so I know where the steam will go, just in case.... Is this setup up and running? If so, have you had any issues with water condensing on the radiator?
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Post by dirtdevil on Jul 7, 2019 6:06:48 GMT -8
What would be the optimal place to put a coil in a heater. Seems like it would be to have the tubing wrapped around the outside of the heat riser allowing for a longer run of tubing and more surface area to absorb heat. My understanding is the point of the exposed metal bell is to cool the gases from the heat riser so that they sink to the bottom of the bell. Having a water storage tank, something like a 100 lb propane tank, welded into the top of the bell and protruding to just above the heat riser would heat a lot of water fast. That would mean the rest of the top of the bell would be maybe six inches higher than the normal 2 inch setting above the riser. I don't know if that would be a problem. I still think that even with a pressure relief valve a closed system is dangerous. 20 years with an open to the atmosphere, wood fired hydronic system heating over 2000 sq ft and never one problem other than pump replacement and flushing the calcium out of the system about every three years.
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Post by patamos on Jul 7, 2019 19:18:43 GMT -8
Ya, gravity cap vented is the way to go. nothing intricate to malfunction - and intricate valves will eventually malfunction. SOme masonry heater builders put big 1.5" or greater tubes into the harvesting mass wall of a bell or flue run body. Slow ramp up. Risk of flash way low. The sheer volume in the tubing also offers some storage capacity for showers and such....
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Post by gadget on Jul 8, 2019 17:20:41 GMT -8
What would be the optimal place to put a coil in a heater. Seems like it would be to have the tubing wrapped around the outside of the heat riser allowing for a longer run of tubing and more surface area to absorb heat. Part of the problem with bare tubing is the lack of surface area. A higher temperature gradient is needed to make up for the lack of surface area. I had good results putting some tubbing above the riser about 8". It was just under the top of the barrel. Still took forever to heat water and I was seeing 900F+ on the outside of the barrel just above the coils so they where seeing some very high temps.
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Post by dirtdevil on Jul 9, 2019 4:37:21 GMT -8
That's why I was thinking about around the heat riser. It would allow for a much greater length of tubing. Of course around the inside perimeter of the barrel would also allow for more length but I thought perhaps there would be more heat generated on the heat riser itself. I have a friend that is off-grid and has a 3/8 copper coil inside a four inch sch 40 riser on a rocket heater. It feeds a 50 hot water tank. It makes a lot of hot water very fast. He fires it once a day for the last three years. So far there is very little deterioration of the steel riser.
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Post by gadget on Jul 9, 2019 20:06:58 GMT -8
I have a friend that is off-grid and has a 3/8 copper coil inside a four inch sch 40 riser on a rocket heater. It feeds a 50 hot water tank. It makes a lot of hot water very fast. He fires it once a day for the last three years. So far there is very little deterioration of the steel riser. That is a wild water heater setup. I bet the tubing sees 1500F and higher inside the riser. I'm guessing the fact that the water coil is pulling heat out of the riser is helping to save the steel.
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Post by dirtdevil on Jul 10, 2019 3:19:33 GMT -8
He has pictures of this set up on another forum but there is no way to transfer them. The coils in the pipe and the fact that he only has to fire it for a short time each day surely helps keep the riser from breaking down. He did have to weld extra quarter inch plates on the burn tunnel because it tended to glow red hot. He feeds the hot water into an heavily insulated salvage water heater tank and has enough hot water for him and his daughters to shower, wash clothes and dishes. There are a lot of on demand wood fired water heaters in Europe. Most of us think we need to keep that water heated 24/7. Not so. It just fattens the pockets of the utility companies.
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Post by gadget on Jul 10, 2019 17:30:35 GMT -8
He has pictures of this set up on another forum but there is no way to transfer them. The coils in the pipe and the fact that he only has to fire it for a short time each day surely helps keep the riser from breaking down. He did have to weld extra quarter inch plates on the burn tunnel because it tended to glow red hot. He feeds the hot water into an heavily insulated salvage water heater tank and has enough hot water for him and his daughters to shower, wash clothes and dishes. There are a lot of on demand wood fired water heaters in Europe. Most of us think we need to keep that water heated 24/7. Not so. It just fattens the pockets of the utility companies. I'm heating an insulated 55 gallon barrel that is used to heat a water storage battery(6 55gallon barrels that are surrounded with soil). Also heating grow beds. I can get the main barrel from about 50F to 100F in about 2 to 3 hours if I'm remembering correct. I would like to get that down to about an hour. Getting the whole 385 gallons up to temp takes many hours. Do you have a link to the forum where the pics are? I would like to check it out.
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Post by dirtdevil on Jul 12, 2019 3:55:06 GMT -8
It's a private homesteading forum and can't be shared but I'll ask him if he will E-mail me the pictures so I can post them here. I have seen similar set-ups on You-tube though. Just a simple J tube heater made of welded plate and pipe. I think the trick is getting the coil bent tight enough to fit inside the riser. I tried to bend a half inch copper tube around the outside of a six inch pipe last winter by freezing water inside the tubing but I must not have gotten all the air out because it kinked in a couple places.
I'm interested in your heated grow beds. I'm setting up a greenhouse with a poured in place 500 gallon aquaponics tank and drain down grow beds on one side and then a dutch bucket set up on top of the RMH bench on the other. A few others I know and myself are convinced that conventional growing is about at the end of the line. We are trying to move all our food production inside in hoop houses and other structures.
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