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Dump Zone design

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by timberr, Nov 15, 2012.

  1. timberr

    timberr Member

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    Finally getting around to adding a thremalsyphone dump zone to my set up for a failsafe incase my back up power has an issue or if the circ on the boiler dies. Looking at baseboard output, looks like 3/4" will get me 680 btu/ft @ 200*. I seem to remember reading somewhere on a post that the dump zone should handle 10% of boiler output, I have an EKO 25 so 10% is 10,000 btu's or about 15 ft of base board, I have plenty of base board so I will probably do 20 or 25 depending on space. Does this all seem reasonable, also is it worth adding some pitch to the dump zone to aid in the flow? If so any suggestion (1/4"/ft?)?

    Thanks for any input.

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  2. 91LMS

    91LMS Member

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    would you really get that many btu/ft though with no circulation other than gravity flow? i am currently designing and piping the same scenario on my install. not trying to derail the thread but possibly my questions will help get you more answers?
  3. stee6043

    stee6043 Minister of Fire

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    You have storage. How is it arranged relative to the boiler? Higher/lower in elevation? I have stacked 500 gallon storage tanks and I get plenty of thermosiphoning through the tanks to make up a "dump zone" with no additional zones needed. I too have battery backup, however.

    Just a thought...perhaps you're already good to go depending on your storage configuration.
  4. timberr

    timberr Member

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    My system is in the basement and the return runs from the bottom of storage up to the 1st floor joist and then down to the boiler so thermalsiphon won't work. 91LMS I agree with you observation, 680 btu/ft is at 1 GPM, I was hoping for some guidance on the length, I think I have 30' of baseboard at my disposal.
  5. heaterman

    heaterman Minister of Fire

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    My humble opinion is that 10% is pretty light for a dump zone. Consider for instance that power off occurs at a point where the boiler is at full output. Is the heat going to dissipate in one minute, five minutes, 15 minutes before the fire dies out? Who knows? Once you get the mass of the boiler itself and the water up at full trot I would think that 10% would be adequate to absorb maybe a few minutes (6?) of output. I would be inclined to think that it will take a bit longer than that to unload the "flywheel" in the boiler. I'm guessing that it would take maybe a half an hour to get the boiler output shut down. Anything however is better than nothing.
  6. Nofossil

    Nofossil Moderator Emeritus

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    It has been shown that the pressure relief is the dump zone of last resort ;-)

    Since most dump zones of the type you describe are installed between joists, I've often wondered if you quickly get a layer of really hot air surrounding the baseboard, further limiting the heat transfer capability. I have no actual experience with this - just wondering.

    I have battery backup for my circ and controller - never got around to installing a dump zone.
  7. maple1

    maple1 Minister of Fire

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    Where are your load supplies/zone pipings in relation to the top of your boiler?

    Mine are pretty well right above the boiler, so I just have my dump circuit plumbed into my house rads. Lots of dumping capacity there.
  8. Bob Rohr

    Bob Rohr Minister of Fire

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    Baseboards need to have the enclosure around them to set up convection currents and I agree on the ceiling mount they really do not have access to that cold air layer that they find when mounted floor level. I'd reduce that output number a lot for ceiling mount, especially if the enclosures are left off.
  9. Floydian

    Floydian Feeling the Heat

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    This is all very interesting. It seems in Euroland they really prefer short runs from boiler to storage with good potential for ThermoSiphon in a power outage. And loading units with low resistance swing check valves to also maximize TS in a no power or pump failure event. Also maintaining good stratification in storage should further help the situation.

    To Heaterman and HR, It would be great to hear your opinions on this type of approach Vs. the N.O. valve with a fin tube gravity dump zone. Or maybe in conjunction with? Basically what would be your ultimate overheat protection plan?(Heaterman, you can't answer Garn,;) I know it solves this problem by it's inherent design).

    Thanks,
    Noah
  10. BoilerMan

    BoilerMan Minister of Fire

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    I thought in Europe they use the cold water coil in the boiler for the dump zone. I assume they also have blow-off valves as well.

    TS
  11. Floydian

    Floydian Feeling the Heat

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    You are correct. I think this is mostly used in places that have "city" water. I am using the coil in my Vedolux 37 because its there and my inspector thought it was a good idea. I can see it helping in a pump failure but not so much in a power outage as I don't have that much water in my system once my well pump is without power. I'll remedy this as funds allow.

    I have had my misgivings about the suspended fin tube dump zone approach and Heaterman and HR have kind of reinforced that. I know I'll have decent thermosiphon from boiler to storage, I just don't know if its enough or if I should add some additional dump zone. I can't say I'm looking forward getting my boiler up to temp and killing power to see what happens, but I am going to. I'll be batch burning as my boiler only feeds storage and the Vedolux can't idle so I figure I'll always want to keep some overheat capacity in storage.

    Sorry to the OP for the hijack,

    Noah
  12. maple1

    maple1 Minister of Fire

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    My ultimate plan was a storage layout like you describe (right next to & top a little higher than the boiler), a laddomat that is conducive to gravity flow to storage in a power outage, and a section of 1" pipe out the top of my boiler tied into my existing zones with a NO zone valve in between. The zone valve is also wired to an aquastat that will break on rise & open it if the boiler gets too hot. My boiler has the cold water coil built in but it's not hooked up.

    Realistically, I don't think I'd need more than the storage/laddomat thing for adequate overheat protection.
  13. Bob Rohr

    Bob Rohr Minister of Fire

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    I tend to agree that a storage tank connected with a 3 way valve/ pump that has an overheat protection gravity check should be plenty of protection. I did install this device on my system and will give it a try on the next fire. I think most modern gasifiers shut down fairly quickly with a power outage, fan and or dampers will close down.

    I installed quite a few Aquatherms and they shut down quickly when the power failed. Unless the door gaskets leaked enough air to keep a small fire going, or someone forgot to latch the door. Most owners needed to learn that lesson only once :)

    Make sure the expansion tank is sized large enough to allow some wiggle room. If you maintain 12 psi in the boiler it will run to about 244°F before it steams. Which is another reason why you don't want to use plastic or pex pipe for near boiler piping. So the expansion tank could be sized from 50°- 240° range and provide some extra cushion.

    I think a large cast iron radiator would be much better than 3/4 fin tube baseboard for a dump, we know those work well on gravity systems and they emit heat energy via radiation and convection, fin tube is a convection only transfer. Unless you have good air movement there is very little energy transfer from fin tube.

    A small fan powered convector would dump much more, but you are back to a backup power source requirement, may as well add the battery powered circ.

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  14. Fred61

    Fred61 Minister of Fire

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    My overheat protection serves two purposes. My overheat aquastat is mounted into the auxillary well on the top of my boiler and is powering a zone that circulates water though a coil in the bottom of my unpressurized storage tank. It is set to launch at about 198 degrees and up until this spring was powered by a 1500 watt pure sine wave inverter/charger with auto switch which was powered by three large deep cycle batteries from my RV. I now have a standby generator but the inverter isn't going anywhere. It's actualy being used as an expensive battery maintainer for all six RV batteries.
    My system only charges the storage so when temperatures in the tank start approaching my high limit which is set at about 185 and the boiler temp starts approaching it's high limit, the overheat circuit kicks on and gives me two sources for transfer of heat from boiler to tank thus reducing idling and speeding up the transfer process.
  15. maple1

    maple1 Minister of Fire

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    I'll also add that my boiler continues firing full hump when the power goes out, since it doesn't have a fan. That's why I've gone what some may think overkill on all my dump stuff.
  16. BoilerMan

    BoilerMan Minister of Fire

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    Maple, I think you have it done right. The only other way would be to have a power-open damper, to shut down the natural draft in the event of a power failure.

    I'd do it exactly as you have done, dump/overheat ZV in a large existing heating circuit that will gravity flow well.

    TS
  17. Floydian

    Floydian Feeling the Heat

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    So, Maple, have you put it to test yet?

    Noah
  18. maple1

    maple1 Minister of Fire

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    Sort of but not exactly. I ran for the first bit with the NO zone valve not wired up, and the flow through that kept my house plenty warm. So I'm pretty sure I'm OK. But I haven't done the 'trial by fire' of loading the boiler up when storage is up to temps & killing the power to everything to see what happens.
  19. timberr

    timberr Member

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    Hi All,

    Been busy in the woods deer hunting, sorry I have been absent in the conversation seeing as I started it. Lots of good stuff has been discussed. Guess I will have to rethink my dump zone plan. No way to use existing plumbing, it would be tough to get a cast iron radiator above boiler.

    I am going to go with the thought that circulators don't just fail, they usually start to male some noise before hand. I have the runaway fire covered, the nobody home when the power goes out and the long term power outage covered. These are the real possible scenarios, the circ failing without warning pretty remote?

    Thanks for the input!
  20. maple1

    maple1 Minister of Fire

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    I did have a circ fail before, once - it just silently stopped turning. I don't know how long it was down before I noticed it since my zones still flowed by gravity.
  21. mmudd

    mmudd Member

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    Here is another overheat scenario for you. Not power related or pump failure. I recently installed a loading unit for return protection. Been working great for past several weeks. Last night I fired up system. Just before bed I checked status and was shocked to see temp at boiler over 210. My overheat aquatstat on fan coil had kicked on as it should I was getting no flow to or from storage. I was getting minimal hot water (140 deg) thru fan coil because it was drawing mostly from and returning to storage. Turns out, my loading unit thermostat stuck. Would not let return water circulate and would not let flow to or from storage. I gave it a couple of slight bumps with a screwdriver handle, and it opened up and cooled down immediately. I'm going to diassemble tonight to see if there is gunk in there since I did considerable pipe work recently. Anybody out there have this type of issue with a theromstatic return protection unit? Don't have dump zone completed yet but it is coming soon after this!
  22. maple1

    maple1 Minister of Fire

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    What type of loading unit is it? Was the pump on it still running?

    These laddomat/loading units are new to me, and I'll admit I don't really know how they work inside - just that there's some kind of thermostat inside. I think in my case, if my NO dump valve at the very top of the boiler opened up, the hot water would work its way up around my zones & back down into the boiler via the supply port of the boiler if the laddomat was somehow blocking flow to the return port. Not ideal, but the hottest water would be going out the top & somewhat cooler water would be coming in not quite at the top. Or, it would come into the bypass loop T then go down the bypass loop & into the boiler return port that way.
  23. mmudd

    mmudd Member

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    Came from Tram Biomass USA. Seems to be a nice unit similar to the caleffi and easy to service with isolation valves & unions at each port, . Can't think of actual name on unit. It has a plug in it to prevent circulation when boiler is cold, so no heated storage water flows thru when fire is out The pump was still running. Because thermostatic valve was stuck, there was no circulation in or out of boiler. Just a couple of light taps opened it up thankfully. I was sure wishin I had my overheat loop in place. At first, I thought boiler temp guage was reading wrong since all other temps were not reading hot, but the fan coil overheat loop on and a very hot pipe caused me to investigat further.
  24. BoilerMan

    BoilerMan Minister of Fire

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    There was a thread about this a few months ago, Heaterman was the one who said it's still a mechanical piece of equiptment and therefore subject to failure. It's basically a thermostat in a car, wax motor pushing against a spring with sheetmetal dick in between. When "closed" the sheetmatal diverts supply water through the bypass pipe back to the return, around and round through the boiler, and no where else. As this water heats up the wax motor opens the sheetmetal disk and closes off the bypass loop as it opens proportionatly the return oprt. This allows water to be sent to the load as well ar some bypassed. Once the water is up to temp the bypass is fully closed by the sheetmetal disc and water is fully sent to the load and fully returned to the boiler.

    TS

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