Thermosiphon and tank placement advice

[scottinkn]

Hello

I am FINALLY about to hook up my wood boiler after an injury last fall woodcutting.(tore my achilles, double ouch)

I am going to build a tank for storage and add solar later. I have 3 choices for tank placement.

2 outside 1 inside.

Inside would be next to the boiler
outside 1 - in the ground on southwest side of house near future hottub (bottom of storage tank would fall about half way up on boiler(22' supply line run)
outside 2 - Above the ground under a deck, bottom of the storage tank will be 1 foot above boiler level.( will have to run lines and feed from the from top of tank (12' long supply line run)
(outside 2 could have attached solar collector right to it)

Piping size looks to be 1-3/4" - 2"

So my first question: is there a great loss in efficiency by trying to thermosiphon?( as outside 2 being the highest tank)
AND is there a great loss in general with outside storage?

Which tank and why?

If pics are necessary let me know.


Thanks,

Tink

 

[Singed Eyebrows]

My tank is less than 3 feet from my boiler, in the basement & works perfectly. What kind of tank are you going to "build"? Sorry on the injury, one of the TKD students snapped out a roundhouse kick & fell down after with a torn achilles. It didn't heal fast, Randy

 

[DaveBP]

Scott, I'm confused. But then, that's not uncommon.

When you say you want to thermosiphon to storage are you talking only in an emergency (when the electric power failed) or all the time the boiler is running? Thermosiphoning doesn't use electricity so will be more efficient than pumping, on an electric bill basis. But transporting all the output of the boiler at full tilt would be something to behold. How big a boiler are you considering? (You used the term 'furnace' which implies a hot air appliance but I assume this is a wood-fired boiler you're talking about).

Is this to be a vented unpressurized tank? Or are you thinking about a propane tank or some other type of pressure vessel?

Outside storage can be insulated so well that the heat loss is small but that will cost more than the same loss indoors. And heat lost indoors is still being used to heat your living space so it's not 'lost' the same as outdoors.

 

[scottinkn]

I want to build a plywood tank for the boiler and I was hoping to thermosiphon to storage while it is running...I know that the tank water level above boiler would be better to do that, thats all.
I just HATE to give up valuable cellar space to a storage tank - but I think there may be no choice. I did just find another option for tank placement and that is under a workbench in the cellar. I would not be really giving up much space but it would be 10 more feet of piping, ah well. As for thermosiphoning - thats probably out as well with the tank being level with the boiler.

(I was hoping to use thermosiphoning to completely circulate the storage but now I do not think that is possible)

 

[Singed Eyebrows]

I want to build a plywood tank for the boiler and I was hoping to thermosiphon to storage while it is running...I know that the tank water level above boiler would be better to do that, thats all.
I just HATE to give up valuable cellar space to a storage tank - but I think there may be no choice. I did just find another option for tank placement and that is under a workbench in the cellar. I would not be really giving up much space but it would be 10 more feet of piping, ah well. As for thermosiphoning - thats probably out as well with the tank being level with the boiler.

(I was hoping to use thermosiphoning to completely circulate the storage but now I do not think that is possible)

From what I have gathered on Hearth, thermosiphon is driven by the heavy cold water running down. You wouldn't have much force with a tank under a bench as you say. You are running unpressurized, could you find a steel oil tank etc that would be tall enough to allow an angle on the pipes? Randy

 

[EffectaBoilerUser (USA)]

I was under the assumption that the tank needed to be at least as high as the boiler to thermosiphon but didn't need to be above the tank.

I will soon be installing an effecta woody lambda 35 with a 500 gallon storage tank placed next to it.

I will be using a laddomat 21 loading valve which has a feature built into it for thermosiphoning in the event of a power failure.

It is my understanding that hot water will flow from the outet on the boiler down through the tank (as it gets cooler) and back into the inlet side of the boiler, thus creating an actual flow which will remove the potentially dangerous hot water from the boiler.

My reasearch has lead me to believe that the most critical item for good flow is to have minimal distance from boiler to tank and minimal restrictions in the piping from boiler to tank.

Can anyone confirm my findings?

Thanks,

 

[Singed Eyebrows]

I was under the assumption that the tank needed to be at least as high as the boiler to thermosiphon but didn't need to be above the tank.

I will soon be installing an effecta woody lambda 35 with a 500 gallon storage tank placed next to it.

I will be using a laddomat 21 loading valve which has a feature built into it for thermosiphoning in the event of a power failure.

It is my understanding that hot water will flow from the outet on the boiler down through the tank (as it gets cooler) and back into the inlet side of the boiler, thus creating an actual flow which will remove the potentially dangerous hot water from the boiler.

My reasearch has lead me to believe that the most critical item for good flow is to have minimal distance from boiler to tank and minimal restrictions in the piping from boiler to tank.

Can anyone confirm my findings?

Thanks,

The boiler output pipe needs to go at an upwards angle to the top tank fitting. The lower(return) should go at a downwards angle. My tank is less than 3' from the boiler with 1 1/2" piping & no problems at all. I run a Lado 21G & couldn't be happier with it. I do run a vertical tank & this is less problems all around. You do not need your tank above the boiler, as mentioned the piping needs to be at an angle though for thermosiphen. Good luck, Randy PS, My secondary loop is thermosiphen going through a non running Grundfoss & some 3/4" copper tubing & moves more water that I ever thought possible.

 

[Chris Hoskin]

thermosiphoning to a tank requires not only vertical rise, but also minimal flow resistance. Because of the huge pipe lengths involved in the heat exchange coils, thermosiphoning to an unpressurized tank is not practical. A vertical, pressurized tank located right next to the boiler will work best.

Also, this is only something to consider for power-outage heat dump when you are trying to dump, say, ten percent of the boiler's output. At full output you cannot expect to see enough flow from gravity alone to charge the tank or keep the boiler from cycling.

Unless you are off-grid, I would suggest that the electrical consumption of this pump is not worth worrying about.

Chris

 

[ewdudley]

...

Also, this is only something to consider for power-outage heat dump when you are trying to dump, say, ten percent of the boiler's output. At full output you cannot expect to see enough flow from gravity alone to charge the tank or keep the boiler from cycling.

Unless you are off-grid, I would suggest that the electrical consumption of this pump is not worth worrying about.

Chris

A gravity-flow boiler with storage system could be realized under the right circumstances, but it would take some tank altitude and planning. It must be possible; a John Deere G with a thermo-siphon cooling system rejects over 100,000 btu / hour out its radiator with only an 18 inch rise of 3" pipe from the top of the block to the top of the radiator.

When I considered the idea, a ballpark design for a 120,000 btu / hour boiler was to have at least about a five foot, straight-shot rise from the top of the boiler to the bottom of the tank. This was using 2" pipe with two elbows in both the supply and return lines, plus necking down to a 1.5" Danfoss located in the return line up at the bottom of the tank. This was for a worst-case scenario of 180 degF at the bottom of the tank and 215 coming out the top of the boiler.

Doable in the right situation, but it wasn't something I could accommodate.

--ewd