Development of a rocket water heating system
Oct 16, 2017 16:45:02 GMT -8
matthewwalker and ronyon like this
Post by permaculturebob on Oct 16, 2017 16:45:02 GMT -8
First, I'm not a very together/organized experimenter, no verified temps or rigorous tests, just the gradual development of a fairly reliable and safe water heating system using a rocket barrel and copper coil.
I started with a 6 inch riser in the barrel and 50 feet of copper coil, connected directly to a water heater tank with Pex pipe. The hot water input (to the heater) was through the fitting for the tpr valve--yes, I was working without a net--boom squish as they say at Permies.
I would put up pictures, but keep getting errors of oversize even with a 40k jpg
the cold water output was through the drain fitting. The regular cold input and hot output on top of the heater were used to connect to the house plumbing.
My plumbing had the option of turning off the pressure to the hot water heater, while still connected on the hot water side, opening the shower hot water valve effectively took pressure off the system.
Anyone experienced with this sort of loose experimentation borne out of necessity immediately sees multiple ways this can go wrong, and almost all, if not all are operator error, so I will immediately enter a disclaimer--don't try this at home....
Over the course of several years I blew holes in the hot water pex pipe where it connected to the copper from the stove perhaps 5 different times, I came to appreciate that section of pipe as my new TPR and started to tiptoe around it whenever I was uncertain.
To say this was an experiment is really not exactly the whole story, being off grid and relatively poor (in money) this was actually my only hot water source. So it was subject to all the stresses of living, that inadvertently gave many variables in the equation.
For instance the time the water was gone from the coil, with no pressure (i forget exactly how that happened) and the primary damage was one of the soldered joints started to leak.
I started out by looking through the internet for verified explosions, the worst was a water valve turned off on the tank of a cast iron stove, a legitimate shrapnel type explosion. I figured a copper coil would not explode like that, but would burst at a seam and send a hot jet into the room. Not especially healthy, but not exactly a house leveling explosion either. Yes I saw the water heater shooting through the roof of a house in that famous training video, but to my mind that looked like something that was staged, with water heater full of water and ALL the valves shut down tight confining the pressure to the heater.
After all this about the unnatural fears around steam release, at this point I will advise anyone thinking about this sort of thing to get a steam whistle or emergency pressure valve of some kind, but maybe not a temperature valve-- I found that importing water at 150F would set the thing off, even if most of the tank was cold
The hot water tank is not really designed to layer the water, hot water goes off at the top, cold water comes in at the bottom. But in a gas heater the heat comes in at the bottom, and mixes the water--- in my arrangement I could get really hot water without having to heat the whole tank.
As time went on I have devised plumbing to more or less provide water directly from the stove, bypassing the tank, a couple loads in the 48 sq inch firebox and there is a small amount of hot water in the coil, and doing dishes or some other task that requires sporadic use of the hot water can keep the coil from getting too hot.
There are all sorts of options. In bypassing the tank I can send the water directly into the floor radiant system if I choose, and then take a bit to wash my hands.
I used a 20$ circulating pump from china with 1/2" mpt (male pipe thread) and a thermostat (10 -20$) also from china, everything is 12 volts. Yes, I'm off grid.
My plumbing is full of valves for lots of different functions and option, but if they are not needed, the fewer valves in the system the better (a valve in the wrong position caused that shrapnel explosion when people operating the stove were ignorant of the valves' existence.
My system does a small amount of thermosiphon activity ,but being 10 feet away from the RMH it is not enough to count on, with no pressure on the system the water would boil out through the tank and then the shower. Which brings me to another safety feature, a bucket of sand to douse the fire immediately in case of a catastrophic failure in the water supply.
The evolution of the system- start with 6 inch riser, too small, especially the firebox which would not hold enough wood--6 inch batch heater will likely be good enough--my longest continuous burn was probably not more than 4 hours, burns were mostly 1-2hrs --
40 feet copper coil- too short for efficient heat transfer add 40 more feet, better, 40 more feet even better, goal would be 160 feet --with a tighter wrap probably approaches instant hot water. Even though I had about ten feet of clay mass bench, the bench seldom got much heat, most of the heat seemed to be extracted by the water coil--exit temps at the outside--100-120 F Top of stove glowing so red at times it scared me
I burned lots of damp wood, lots of rough sticks, occasionally real nice pieces of oak, but mostly trash wood--doing the smell test there was some smoke, but mostly pretty clean.
After about an hour of burning (depending on how on top of keeping the fire going I was) I would have enough hot water for a long luxurious shower, with water left over for dishes or whatever. It took several hours to warm the radiant concrete floor mass of a 12x12 room by 5 or 10 degrees.
The pump was www.ebay.com/itm/Solar-DC-12V-24V-Hot-Water-Circulation-Pump-Brushless-Motor-Water-Pump-700L-H-/182748855975?hash=item2a8cae3ea7 or www.ebay.com/itm/DC-12V-Solar-Hot-Water-Circulation-Pump-Brushless-Motor-Water-Pump-/201985169076?hash=item2f074116b4
the thermostat was also from ebay (china), but I can't find a link, adjustable almost to boiling, I usually work in the 150 range, sensor placed between top two coils, close to the barrel, but usually not touching it so it is mostly reading water temps. it could turn stuff on or off, but mine turned on the circulating pump, ran for 10 degrees F then turned off, but by that time the cold water had infiltrated the coil almost completely. This is something I figured out as I went along.
I actually operated the pump manually for most or maybe all of the first year, that was when most of the blow outs occurred.
Like I have mentioned, remembering to have all the valves in the right position is essential.
Oh, one interesting thing with those small centrifugal pumps--they will stop if there is any air in the line. Having the intake to the pump come out the bottom of the water heater allows any air bubbles in the system to rise and fill the tank first.
They also clog pretty easy-- I had one stop pumping, and took out the four screws,took off the cover and pulled out a wad of hair, then put the screws back and started pumping again. If I had known what to do it would've taken five minutes and no lost water or anything. As it was I went into emergency mode, suffocated the fire and ran around like a chinese fire drill for 1/2 hr before I got up the nerve to take the pump apart. overall I have been impressed with how rugged and reliable. I had one motor fail when it was energized while submersed --burned up the circuitry -these are brushless motors-- and one pump failed when I broke off the outlet--both were actually my fault.
Even though these pumps are rated for hot water, I thought it prudent to operate them on the cold water side, pushing the water through the coil.
After three or so years with the thermostat and wiring that is always substandard, I devised a safety sort of thing, so when I'm starting a fire there is an LED light right next to the firebox--If it's not on, the pump circuit is not energized (even if I have thrown the switch.
I also have the plumbing set up so I can use the house water pressure used to empty a hot coil of water if anything on the pump circuit fails, also a place where I can by pass the thermostat and start the pump if it seems wonky.
At some point maybe I can figure why this thread won't let me upload pictures, but for now I think I'll stop and do some more reading.
By the way have I mentioned just how much I have gotten out of all the contributions, and hope in some small way I can maybe contribute something to others --at least in saving them some of my dead ends
I started with a 6 inch riser in the barrel and 50 feet of copper coil, connected directly to a water heater tank with Pex pipe. The hot water input (to the heater) was through the fitting for the tpr valve--yes, I was working without a net--boom squish as they say at Permies.
I would put up pictures, but keep getting errors of oversize even with a 40k jpg
the cold water output was through the drain fitting. The regular cold input and hot output on top of the heater were used to connect to the house plumbing.
My plumbing had the option of turning off the pressure to the hot water heater, while still connected on the hot water side, opening the shower hot water valve effectively took pressure off the system.
Anyone experienced with this sort of loose experimentation borne out of necessity immediately sees multiple ways this can go wrong, and almost all, if not all are operator error, so I will immediately enter a disclaimer--don't try this at home....
Over the course of several years I blew holes in the hot water pex pipe where it connected to the copper from the stove perhaps 5 different times, I came to appreciate that section of pipe as my new TPR and started to tiptoe around it whenever I was uncertain.
To say this was an experiment is really not exactly the whole story, being off grid and relatively poor (in money) this was actually my only hot water source. So it was subject to all the stresses of living, that inadvertently gave many variables in the equation.
For instance the time the water was gone from the coil, with no pressure (i forget exactly how that happened) and the primary damage was one of the soldered joints started to leak.
I started out by looking through the internet for verified explosions, the worst was a water valve turned off on the tank of a cast iron stove, a legitimate shrapnel type explosion. I figured a copper coil would not explode like that, but would burst at a seam and send a hot jet into the room. Not especially healthy, but not exactly a house leveling explosion either. Yes I saw the water heater shooting through the roof of a house in that famous training video, but to my mind that looked like something that was staged, with water heater full of water and ALL the valves shut down tight confining the pressure to the heater.
After all this about the unnatural fears around steam release, at this point I will advise anyone thinking about this sort of thing to get a steam whistle or emergency pressure valve of some kind, but maybe not a temperature valve-- I found that importing water at 150F would set the thing off, even if most of the tank was cold
The hot water tank is not really designed to layer the water, hot water goes off at the top, cold water comes in at the bottom. But in a gas heater the heat comes in at the bottom, and mixes the water--- in my arrangement I could get really hot water without having to heat the whole tank.
As time went on I have devised plumbing to more or less provide water directly from the stove, bypassing the tank, a couple loads in the 48 sq inch firebox and there is a small amount of hot water in the coil, and doing dishes or some other task that requires sporadic use of the hot water can keep the coil from getting too hot.
There are all sorts of options. In bypassing the tank I can send the water directly into the floor radiant system if I choose, and then take a bit to wash my hands.
I used a 20$ circulating pump from china with 1/2" mpt (male pipe thread) and a thermostat (10 -20$) also from china, everything is 12 volts. Yes, I'm off grid.
My plumbing is full of valves for lots of different functions and option, but if they are not needed, the fewer valves in the system the better (a valve in the wrong position caused that shrapnel explosion when people operating the stove were ignorant of the valves' existence.
My system does a small amount of thermosiphon activity ,but being 10 feet away from the RMH it is not enough to count on, with no pressure on the system the water would boil out through the tank and then the shower. Which brings me to another safety feature, a bucket of sand to douse the fire immediately in case of a catastrophic failure in the water supply.
The evolution of the system- start with 6 inch riser, too small, especially the firebox which would not hold enough wood--6 inch batch heater will likely be good enough--my longest continuous burn was probably not more than 4 hours, burns were mostly 1-2hrs --
40 feet copper coil- too short for efficient heat transfer add 40 more feet, better, 40 more feet even better, goal would be 160 feet --with a tighter wrap probably approaches instant hot water. Even though I had about ten feet of clay mass bench, the bench seldom got much heat, most of the heat seemed to be extracted by the water coil--exit temps at the outside--100-120 F Top of stove glowing so red at times it scared me
I burned lots of damp wood, lots of rough sticks, occasionally real nice pieces of oak, but mostly trash wood--doing the smell test there was some smoke, but mostly pretty clean.
After about an hour of burning (depending on how on top of keeping the fire going I was) I would have enough hot water for a long luxurious shower, with water left over for dishes or whatever. It took several hours to warm the radiant concrete floor mass of a 12x12 room by 5 or 10 degrees.
The pump was www.ebay.com/itm/Solar-DC-12V-24V-Hot-Water-Circulation-Pump-Brushless-Motor-Water-Pump-700L-H-/182748855975?hash=item2a8cae3ea7 or www.ebay.com/itm/DC-12V-Solar-Hot-Water-Circulation-Pump-Brushless-Motor-Water-Pump-/201985169076?hash=item2f074116b4
the thermostat was also from ebay (china), but I can't find a link, adjustable almost to boiling, I usually work in the 150 range, sensor placed between top two coils, close to the barrel, but usually not touching it so it is mostly reading water temps. it could turn stuff on or off, but mine turned on the circulating pump, ran for 10 degrees F then turned off, but by that time the cold water had infiltrated the coil almost completely. This is something I figured out as I went along.
I actually operated the pump manually for most or maybe all of the first year, that was when most of the blow outs occurred.
Like I have mentioned, remembering to have all the valves in the right position is essential.
Oh, one interesting thing with those small centrifugal pumps--they will stop if there is any air in the line. Having the intake to the pump come out the bottom of the water heater allows any air bubbles in the system to rise and fill the tank first.
They also clog pretty easy-- I had one stop pumping, and took out the four screws,took off the cover and pulled out a wad of hair, then put the screws back and started pumping again. If I had known what to do it would've taken five minutes and no lost water or anything. As it was I went into emergency mode, suffocated the fire and ran around like a chinese fire drill for 1/2 hr before I got up the nerve to take the pump apart. overall I have been impressed with how rugged and reliable. I had one motor fail when it was energized while submersed --burned up the circuitry -these are brushless motors-- and one pump failed when I broke off the outlet--both were actually my fault.
Even though these pumps are rated for hot water, I thought it prudent to operate them on the cold water side, pushing the water through the coil.
After three or so years with the thermostat and wiring that is always substandard, I devised a safety sort of thing, so when I'm starting a fire there is an LED light right next to the firebox--If it's not on, the pump circuit is not energized (even if I have thrown the switch.
I also have the plumbing set up so I can use the house water pressure used to empty a hot coil of water if anything on the pump circuit fails, also a place where I can by pass the thermostat and start the pump if it seems wonky.
At some point maybe I can figure why this thread won't let me upload pictures, but for now I think I'll stop and do some more reading.
By the way have I mentioned just how much I have gotten out of all the contributions, and hope in some small way I can maybe contribute something to others --at least in saving them some of my dead ends