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Why "no storage tank"?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by jklingel, Dec 4, 2007.

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  1. jklingel

    jklingel Feeling the Heat

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    I have gotten emails from two of the boiler manufacturers often mentioned here, and both say "Storage? Most of our customers never ask for/about that." One even said "Storage is over-rated." Any idea why these two folks aren't hot about storage tanks? (Both of these guys have + feedback from some of you). This just seems odd to me. The concept sounds excellent to me.

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  2. Nofossil

    Nofossil Moderator Emeritus

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    I would hesitate to try and second-guess the reasons behind the responses that you mention. The first may be quite true - I'll bet that very few customers ask for or about storage. It's not exactly a mainstream concept yet. It adds considerable cost and complexity to an installation, so it might well put people off if they thought that it was a necessary part of an investment in wood heat.

    We're lacking in hard data about increased efficiency from the use of storage, but I'd say that in my case it will never pay off in terms of wood savings.

    It may be that some boiler designs don't experience a large difference in performance (efficiency, creosote production, fumes) between idling and full-bore operation. The prevailing theory is that gasification boilers shouldn't idle too much, so heat storage is a way to accomplish that. Perhaps it's no big deal for other boiler types.

    For my part, my EKO seems to idle pretty well. I used it my first season without storage.

    The huge benefit of heat storage for me is that the house temperature stays constant. I'm sitting here at 6:30 in the morning in my t-shirt and the fire's been out since 9:00 last night. At some point I'll have to build another fire, but I'll decide based on storage tank temp, not complaints from the inhabitants. I'll also have a pretty wide window for building the fire. I could do it now, or wait until late tonight. It's 15 degrees right now, so I probably can't skip a day, but if it were a bit warmer I could got two or sometimes three days between fires.
  3. Eric Johnson

    Eric Johnson Mod Emeritus

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    As nofossil suggests, I think if you're trying to compete with OWBs, which typically don't use storage, it's probably best not to bring it up until you get the potential customer committed to gasification. Like nofo says, you can get by without the storage, but most people will want to add some eventually. I look at it like air conditioning and cruise control in a car: You don't need them, but they sure make long drives in hot weather a whole lot more tolerable. The nice thing about hot water storage is that you can add it later.
  4. verne

    verne Member

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    At what temp. of storage tank do you start a fire?
  5. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    That should be determined based on what sort of radiation you have, and the outdoor temperature. Baseboards need higher water temperature than something like radiant floor heating. Under full load, baseboard heat is going to be sized for 180-degree water, whereas radiant floor heating will be sized for something in the 100-degree range (depending upon the actual system).

    Outdoor temp also plays a role. You don't need the full "design" water temperature (sized for 0-10 degrees outside, in your area) when it's 50 outside.

    It's best, initially, to wait until you start to notice an indoor temp drop, and then make note of the storage tank temp and the outdoor temp. Do this a few times, and you can make a graph. It should end up being a pretty straight line that you can extend in either directions to handler warmer/colder outdoor temps than your "sample" conditions.

    Then just look at the outdoor temp, find the water temp that matches, and that's your "start a fire" temp. Plan for some lag time between starting the boiler, and it actually bringing the tank up to temp.

    Joe
  6. Nofossil

    Nofossil Moderator Emeritus

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    It's pretty simple - I just plug in wind speed, sunlight intensity and direction, outdoor temperature, tank temperature and predicted outdoor temperature six hours in the future into a handy fourth-order polynomial and calculate the heat extraction curve. When the first derivative approaches zero, I start a fire ;-)

    Actually, I've learned what to expect pretty much as Joe describes it. I don't have any radiant zones at present, and baseboards can't keep up if the tank temp is below 120 or so. The 'or so' depends on how cold it is outside. I'm at about 130 now with an outside temp of 17, so I'll run out of heat in a few hours. Since I'm by myself, I'll put on a sweater and plan to buiid a fire mid-afternoon so it'll be toasty when the girls get home.

    When I add my radiant zone, I'll be able to keep the main floor comfortable down to a tank temp of 100 or so, and I'll have more flexibility.
  7. Jim Post

    Jim Post Member

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    I have a Tarm Solo Plus 30 that I installed in 2005. We didn't add storage for a variety of reasons...primarily cost...but also space...finding room for 500 gallons of water inside our house would be difficult. I figure we can always add storage later if we found stoking to be overwhelming. So far, it has been manageable, we definitely had a learning curve to overcome that first year...anticipating the heat needs for the house and loading accordingly. Even last season, there were times when we'd let the Tarm get too cool before reloading...leading to slow recoveries. This season has been much better...we are using more seasoned (drier) wood and have been running the boiler a little hotter. I say if you can afford storage go for it...storage complicates installation but simplifies operation.

    JP in WI
  8. Nofossil

    Nofossil Moderator Emeritus

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    Welcome to the forum. You installed your Tarm at about the same time I installed my EKO. In my view, the primary benefit of the storage is to improve the livability of the system. We have more flexibility about when to build a fire, and temperature control is via the thermostat. Major increase in WAF - search the forum if the acronym is unfamiliar ;-)
  9. Eric Johnson

    Eric Johnson Mod Emeritus

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    Welcome to the Boiler Room, olpotosi. It's always good to have another Tarm user around here.

    I would second your thoughts on timing without the benefit of storage. A little experience and advance planning goes a long way, I've found.

    Heating with wood is all about momentum and using it to your advantage.
  10. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    My house is nothing but radient, and my experience has been that it's not 'the greatest thing since sliced bread" I think there are a plethora of heating contractors out there that only have experience INSTALLING it and the BS the suppliers feed them. You need at least some sources of hot air - note: if ya drop the WAF way down, you get either hot air or cold shoulder - especially near entrys and in rooms with cathedral ceilings.

    I will say that I think - obviously I ain't no 'spert :lol: - that a storage tank makes sense for allowing full-throttle clean burns. Also for timing your burns around your schedule and for using wood when the outdoor temps are warm. But storage will not appreciably help an undersized boiler unless the heat demand is only high for a short time. Run the numbers on the BTUs in your storage tank and see how long the tank alone could heat your house. After that amount of time, your boiler is solo.

    Can I get some change back from my two cents??
  11. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    A properly designed radiant system does not need supplemental air, unless the geometry of the room prevents the installation of sufficient radiant surface.

    The design should account for entry losses and ceiling height. Proper radiant isn't simply "staple some tubing to the floor and run water through it." It requires an engineered plan and it needs to be installed according to that plan.

    Joe
  12. Nofossil

    Nofossil Moderator Emeritus

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    Dang - that WAS my plan!
  13. Eric Johnson

    Eric Johnson Mod Emeritus

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    I couldn't do that in the greenhouse even if it did have a cellar underneath it.

    I'm wondering if I need to pour a concrete floor and then put the cement board with the pex on top of that, and tile on top of that, or if I can get away with not using the concrete. I also need to put a drain in the floor.

    Any suggestions on the best way to do this? Right now the floor is a combination of bricks and gravel.
  14. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Insulation first, then cast the pex into the concrete, then put tile on top of that.

    Alternately, build the floor up - install pressure-treated joists and use WarmBoard as a subfloor on top of that.

    Depends on your ceiling height.

    Joe
  15. Nofossil

    Nofossil Moderator Emeritus

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    I was waiting for Joe to chime in, just to make sure that I didn't suggest anything he'd have to contradict.

    My analysis says that heat loss is a problem only around the edges, and that the mass of the concrete is a Good Thing. A couple of inches of foam board under the slab and some sort of thermal break between the slab and the outside, and you should be good to go. Warmboard is neat stuff, but the mass of the slab is great if you have (or can make) the headroom.

    My brother's workshop and house are made that way - works great.
  16. Eric Johnson

    Eric Johnson Mod Emeritus

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    I can make as much headroom as I like with a shovel, but I like the concrete-over-insulation board idea. If I put 2 inches of good foam board down on top of a tamped gravel base, how many inches of concrete should I put down? Any need for stress relief in the slab?

    And as I understand Joe, you put the pex in place and pour the concrete over it?
  17. Jim Post

    Jim Post Member

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    Thanks for the welcome...WAF....seems like it should be Wife Acceptance Factor but I am just guessing....could be Wild A** Fluctuations too I suppose :)

    My wife is on board....she sees the $$ saved with no LP heating and electric hot water heater costs with the Tarm going. Wear and tear on my old bones laying in the wood supply doesn't seem to enter into the equation though. ;-)

    I was recently surprised by how much electricity it takes to keep our heating system going....we were working hard to conserve kwhs and got down to 2 overnight...but couldn't get lower. That was with our refrig, tv, computer, unplugged. Heating system only...two b&g;pumps and the draft fan on the Tarm.

    In a power outage, what do you folks do to keep your boilers going?

    JP in WI
  18. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    You should have a vapor barrier, too. Barrier, then insulation, then concrete. Make sure the vapor barrier is good quality, and preferably use a couple layers, as you don't want ground water sapping heat away from the slab.

    As nofossil mentions, you definitely want to use the edge barrier, as well (typically, more foam that is installed as part of the form, which simply stays when the slab is done). Dig a trench around the edge, allowing the foam to extend down vertically into the ground.

    Typically, the pex is zip-tied to the wire reinforcing grid. If not, it will float.

    For a greenhouse, we typically use 1/2" tubing, 6" on-center. You'll not that the bend radius would prevent that, which we solve by alternating at one end. In other words, if the mechanical layout of the rows is 1-2-3-4-5-6, the actual tubing will go down row 1 then up row 4, then down row 2, then up row 5, then down row 3, then up row 6. That eliminated risks of kinking the tubing (even if you have it set up perfectly, the flow of the concrete might push it too far), and helps to reduce any temperature gradient across the floor.

    As I've also mentioned, you can case tubing into raised planting beds/tables if you want. Warm-rooted plants don't mind cooler air temp, and that saves fuel by reducing heat loss through the glass.

    As far as the thickness and type of concrete, I'd suggest talking to someone with experience pouring slabs. I just tie the tubing to their reinforcing grid, then stand back and let them work. I've never seen stress relief used in a radiant slab, though, and I expect it would need some precautions to prevent tube-shearing, if it were mechanically necessary.

    Regarding the "mass," radiant works best as either a high-mass (concrete) or low-mass (Warmboard, etc.) system. The first works best when the whole system is high-mass (eg, with a storage tank), and is sometimes even set up for continuous circulation, with hot water injected into the loop on an as-needed basis. The low-mass radiant allows for quicker response, if you want to turn the temp down and them back up. Re-heating a slab wastes energy, so it's best to keep those sort of installations at a constant temp.

    Joe
  19. jklingel

    jklingel Feeling the Heat

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    The system that is most commonly used up here, apparently, is (1) good vap barr (2) blue foam (3) pex, stapled to blue foam, (4) wire mesh (5) 4" of concrete, unless you are driving rigs on it, in which case an engineer decides the thickness of the slab, the amount and size of mesh and rebar.
  20. Eric Johnson

    Eric Johnson Mod Emeritus

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    Great information, Guys. Thanks. And sorry for hijacking your thread, jimbo.

    With the low water temps possible with infloor radiant, I would think that constantly circulating from a tank with some kind of mixing valve makes a lot of sense. On sunny days, you probably wouldn't need to circulate water through it, however, as the greenhouse can get up close to 100 degrees. Maybe I should use black floor tile and try to recover some heat during the day.

    On the WAF, I think that can go either way. And sometimes, they go together, as in: The WAF is subject to WAF.
  21. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    If you use a mixing valve system, the pump is usually controlled by a thermostat.

    And yes, you can use the greenhouse as a heat source, to a certain extent. Only when the slab is hotter than the water temperature, obviously. But not much hotter - the sheer amount of tubing makes for efficient heat transfer, even when there is only a few degrees of difference.

    Putting radiant tubing in the concrete patio around an in-ground pool is becoming popular in some areas. It heats your pool and cools that roasting-hot concrete at the same time.

    Joe
  22. rreihart

    rreihart New Member

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    Sliced bread is pretty hard to compete with, but I put radiant under the floor in an addition and the entire family loves it. The thermostat on the wall says the same as the rest of the house but the radiant is definitely more comfortable. I did use aluminum plates to sandwich the tubing to the floor which I think helps a lot. I think the plates are often skipped because they can be kind of pricey. Working in a fabrication shop gives me access to some pretty good equipment so I was able to form my own.

    I know this has no relevance to a poured slab in a greenhouse, but I felt like throwing in $.02.
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