Help on plumbing for thermosiphon

Thanks Freddy, it's not really a big deal to put it back on at the tank. Just wanted to check. As long as I have it off, I will also replace it with a new one. I'm not sure how old it is.

Jeff

I GET IT....I GET IT PHEEEEW
I've been losing sleep over this.That seems like a good system to me for a boiler.I wouldn't have any concerns about cold water going through the coil first(coils in boilers do this all the time).Check valve on the bottom of the tank stops cold water from entering the bottom of tank when
hot water tap is open.Check valve on cold water inlet forces cold water from the bottom of the tank(when graviting)to go through coil

The thermosiphon only happens at the bottom of the tank(because of drip tube)but thats OK because the hot water in the tank will rise and keep the tank hot.

I see now that if you hook the hot comming out of the coil to the hot of the tank the thermosiphon MIGHT work better(hot water durning thermosiphon wouldn't have to go through drip tube).
DON

And 1 other thing to debate,
Hooking the hot from the coil(thermosiphon mode)to the hot or cold on the water tank.
Hooking it to the cold I think would be better.The thermosiphon only takes place in the bottom of the tank(because of the drip tube) so it is like (self tempering the hot from the coil).
I LIKE IT
Anytime you can do something passive I like.
DON
Sorry it took so long to get my brain around this.See you can teach an old dog new tricks!

Richard S. wrote:

BIG BEAM wrote:like a good system to me for a boiler.I wouldn't have any concerns about cold water going through the coil first(coils in boilers do this all the time)

And that's really the only thin that is debateable, is it worth for a small coil and/or can the cold water damage the smaller coil.

I don't think the benefit on a stove or furnace would be that much.And as I posted before sweating MAY be an issue.
I don't think the SS coil would be affected by the cold water(thermal shock).
Are thoes SS coils made of tubing or pipe?

I look at some of the proposed thermosiphon piping and wonder where in the world these ideas came from. A fluid thermosiphon works by the fluids density decrease when it is heated. The less dense fluid will rise and flow to the highest point. When it cools, it falls to the lowest point. The pressure force created is small so every effort should be made to reduce piping friction and temperature loss. When using a regular domestic hot water heater as a storage tank the supply from the stove coil should enter the top of the tank in an unobstructed tapping. Usually the only one present is the PRV tapping. You can't use the cold water inlet because it has a dip tube. You don't want to use the hot output because when you turn on the hot water, the house water pressure causes flow out of the tank stopping the thermosiphon action. Removing the PRV from it's own tapping will violate the plumbing code. But, before water heaters had tappings for the PRV only, the PRV was installed in the straight end of a tee mounted with a close nipple in the tank's output. Pipe the stove coils supply side to the previous PRV tapping. Hot water supply is taken from the side port of the tee that now mounts the PRV. Be sure to use a long temperature sensor PRV. You want it to reach into the tank water if possible. Insulate around the tee. The object is to reduce heat loss so the PRV sees the tanks water temperature.

The return to the stove coil should come from the tanks bottom drain tapping. Remove the boiler drain and replace with a tee. The side port of the tee should go to the stove coil return. The boiler drain should go in the straight through port of the tee.

Remember the thermosiphon force is small, so use smooth wall pipe, i.e. copper to minimize viscous friction. Consider using a larger pipe size, 3/4" or larger. Use long sweep 90 deg el's. Consider using a pair of 45 deg els to turn a corner. Do anything to reduce pipe length and internal flow restrictions. Insulate the hot supply line between the stove coil and the tank.

Pipe the rest of the storage tank as you would normally. Backflow dual check on the cold inlet, bladder tank, etc. if required by your local plumbing code.

Ok here we go again. This is how it is currently setup. If this will work, it's going to stay. Hot & cold in and out of tank like a regular water heater. Water out of drain to bottom of coil. Out of the top of the coil and into the opening for PRV. Added PRV at hot out of coil and replaced PRV at the tank with a new one. Old one had a little build up in it so I just replaced it. Pic is a little blurry but you should be able to see ok. P.S. I have not soldered the connections yet just in case. Also don't pay any attention to the angle that the PRV at the tank it's not soldered in place yet and keeps falling out.

Jeff

yanche,
These systems are simple but if you look at some of the stuff thay did years ago it's interesting.Stove on 1st floor tank in cellar.This may be useful to some people.

Richards system is also a GREAT idea.The water going into the tank is hot enough to be used as DHW.All the thermosiphon has to do is keep the tank hot.If I had a boiler that's the system I would use.(NOW THAT I GET IT).It's better than thermosiphon alone.
DON

You could but the P+T(Freddy) valve closer to the tank but that's fine.
OPEN THE WINDOWS AND FIRE THAT BABY UP!
DON

Lets see close up pics of the solder joints,you should be a pro at this by now!
DON

Cecil, that is perfect.

Big Beam: this statement is incorrect: "The water going into the tank is hot enough to be used as DHW" This is not the case with a simple 'U' pipe in a stove.. that is what this topic is about.. the only way that statement is correct is if the coil is an instant water heater imersed in a boiler's hot water.
The simple Hilkoil 'u' pipes can only add a few degrees to water flowing through the tube.. it is the slow and steady, repeated flow through the tube that gets the water ever hotter and brings a tank full of water up to 140*+. Depending on stove temps, water flow rates, water volume and temperature rise needed, this may take an hour or two or all day..

Greg L.

It's looking close, but the T&P on the tank should be closer doncha think? It's not going to sense temp from the tank very well way up there. Of course after it's done the T&P's will be piped to someplace safe? I think back along you mentioned piping them down. Good.

Wooohooo! Big Beam got his head wrapped around it! (Me too, I learned a thing or two)

Greg
I was talking about a coil in a boiler.Like Richard's parents system.
DON

Does any body know why they put a flow controll valve on hydronic heat systems? Because without one the heating system would be a thermosyphon system. You cannot put check valves on thermosyphon sustems, they block the stratification action of the whole process. As far as how long it takes to heat a tank of water, HilKoil web page has diffrent size coils for diffrent size tanks, but all say it takes about 8 hr to heat the tank of water per coil size. Putting the cold water directly to the coil will cause undue metal fatigue, and would possibly cause the coil to split or rupture. In my early years as a plumbing apprentice I dismantled a couple of Bucket-a-day thermosyphon systems, none were as complicated as what you are trying to do. They are very simple systems to st up, and maintain if done correctly. Cold water in to the tank, Hot water out of the tank, 1 simple loop through the heater in and out of the tank. Thats it. The only diffrence since the turn of the century is now we add relief valves for saftey. Anything more is just a waste of time and money.

ps. I even saved on of the systems, and use the tank on my dads DHW system with a small Grundfoss pump and a tankless heater on his large oil steam boiler. It works so well that the oil waterheater rarely ever runs in the winter. Did i mention his house is a 4 unit complex.