1,000 Gallon Storage Tank as Dump Zone

[DenaliChuck]

Would two 500 gallon propane tanks on end be suitable for a power failure dump zone if half the tank is higher than the Solo 60 boiler?

Since the Tarm is about 4' high and I could place the tanks so there is 4' of tank above the boiler top, could gravity be used to pull the cold water at the bottom of the tank into the boiler during a power failure?

Could this work as a pump-free way to charge the tank during normal operation?

Thanks for your advice!

 

[pybyr]

seems like a sufficiently big tank could serve as a dump zone as long as you have short, large diameter pipes that rise from both the inlet and outlet of the boiler to their respective connections to the tank- hot water has to be able to rise, with no intervening in-line dips, from the hot outlet, and cold water needs to be able to fall, again, with no intervening dips, to get active assured gravity flow.

I am thinking of maybe doing something similar with a smaller tank, still not sure

gravity _might_ be a way to charge a storage tank- but again, you'd have to follow the above principles of effective gravity flow- and the same would go for some BIG pipes between the 2 vertical propane tanks-- and you should ask Tarm to be sure whether gravity flow will provide enough flow to avoid hot spots internal to the boiler. I know Econoburn says gravity-based operation is a no-no except for the "fallback" of a dump zone to be used only in power outage conditions

and it also seems like you'd not want to use your regular storage for the dump zone. If murphy's law strikes and the power fails when your storage is already quite hot, but you've got a big fire going still, then the storage is not going to offer much of a ready "heat sink" for BTUS to quickly go

 

[DaveBP]

I think Trevor has it right. To put numbers to it, if the top of the tank is ten feet above the boiler and the tank is completely filled with 60F, and the boiler is gushing boiling water the pressure driving the thermosiphon is only going to be about 1/6 PSI. Even with big pipes this isn't going to suck up the full heat output from a Tarm 60. If the power fails, the draft damper will close, but not completely cut off the air so it will continue to burn. How hot, I don't know. Tarm says to plan your emergency dump to take 10% of the full capacity. That's almost 20K BTU for your boiler. I'm in this situation in my design (still in the planning stage). I have a Tarm 40 and 1000 gallons of propane tank pressurized storage to hook up. I want to set it up to use the tank to help take the emergency load but not rely on it to take it all in case everything goes wrong all at once. A lot of the European systems I've seen schematics of online use the boiler "loading unit" circulator device which has a flap valve which opens when the power's out and allows whatever thermosiphon the system has to work. I don't know if that's all they rely on that in emergencies. Hansson might answer this question.
But I don't think I'm too far out on a limb to say there's no way a thermosiphon/storage tank setup will replace circulator pumps in a boiler system.

 

[DenaliChuck]

Thanks...once again, if its too good to be true, it probably isn't!

 

[pybyr]

The Econoburn manual does specifically reference and endorse use of a gravity-configured system for, but only for, power-failure dump zone purposes. Not sure what the other makers say.

so gravity for a dump zone is not necessarily out of the question - it's just dubious as to whether your storage tank is the way to go, or to count on, for dump purposes

I recall one evening last week I bumbled across some portion of the HeatingHelp Web site that had various scanned documents of a historical nature, and one of them was a dozen-page or so well written excerpt from some _old_ book SPECIFIC to how to design well-functioning gravity hot water heating sustems. I am sure you could track it down, and it might offer some good food for thought on what you could do for some form of gravity zone for dump purposes.

 

[mtnmizer]

In a conservation I had with the boiler tech at Econoburn about configuring
a powerout dump zone, he said to just tee into the biggest zone(provided it
is of sufficient capacity) with an automag
valve/check valve and it would take the load. In my case the largest
zone (1" line) is over 50'@ 600btu's/ft =ing 30k btus. Will there be
enough flow via thermosiphon?

I dunno. The piping going up and down to each heater is the worry.

My plumber/installer suggests using a "garage heater" for the powerout zone..

Battery backup+a 25' zone? Double safe? MM

 

[kgryder]

If you have two tanks just have one well above the stove and the 2nd tank empty and below the boiler. With power loss the water could just flow from one to the other through the boiler. When the power returns you can just pump the water back to the upper tank. If you plumbed it though one of your zones you could still heat the house during the cool down.
If you have plenty of water you would only need the one tank and just dump the water into the woods or yard. When the power returns you could refill the tank.

 

[pybyr]

If you have two tanks just have one well above the stove and the 2nd tank empty and below the boiler. With power loss the water could just flow from one to the other through the boiler. When the power returns you can just pump the water back to the upper tank. If you plumbed it though one of your zones you could still heat the house during the cool down.
If you have plenty of water you would only need the one tank and just dump the water into the woods or yard. When the power returns you could refill the tank.

in terms of flow, that'd work nicely, and I have been thinking of something along those lines

what I wonder and am concerned about, though, is, taking a near boiling-hot boiler and suddenly, almost instantly, hitting it with a large volume of water about 120-140 degrees cooler, seems like quite the thermal shock- with associated physical stress- for the metal itself, and any seals and gaskets

as I understand it, the goal of a dump zone is ideally a gradual "soft landing" for the boiler once it loses the powered systems that normally dissipate its heat output, and as the fire settles down (more slowly than the loss of the circulators) and eventually slowly burns out without the air that the gasifiers' electric blower was feeding it.

The 2-tank system to hit it with a big whoosh of room temperature water seems like it'd risk being nearly as physically harsh on the boiler as letting it hover at/ near boiling (what you risk without a dump zone)

 

[pybyr]

Denali Chuck and others- see the prior thread that I'd started, titled "dump zone suggestions please"

the more I think about it all, the more I realize that Hot Rod nailed it, in terms of overall short run and long run simplicity and effectiveness and cost, with his idea of a "fallback" 12 volt battery + 12 volt circulator

 

[8nrider]

i just recently but a used tarm mb 55 (oldy but hopefully a goody) i live in the new england woods and i rely on my generator for power back up. very little kw but saved my butt many time.