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Storage Benefits and Idling Concerns...

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by KenLockett, Dec 21, 2012.

  1. KenLockett

    KenLockett Member

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    OK, I have maybe what some might consider a stupid question, but I am a little confused as to why idling for reasonable periods of time (i.e 30-60 minutes versus 2-4 hours) at specific conditions is so bad for a gassifier type wood boiler. By specific conditions I mean correct draft and dampers closed/draft fan off such that combustion is inhibited in firebox.

    I have a Tarm Solo 40 Plus with Storage and have been up and running for a little over a hear now and other than a good coating of shiny creosote in the firebox (which I have been told by other users and the OEM is normal - was very concerned in the beginning), have no issues with creosote in my secondary chamber or flue.

    When my unit idles I assume combustion is inhibited since I have absolutely no smoke from the chimney and the metal flue section from the appliance to the chimney cement flue is cool to the touch (obviously not immediately but into the idle cycle).

    After much time spent on the forum with many members citing the benefits of storage and issues with idling I have become obsessed with proper loading such that idling time is reduced even to the point of adding a temperature controller and micro-PLC to allow me to time my firing and idle periods including counting number of firing/idle cycles. Also monitors temperature of boiler supply with time delay to drive an alarm buzzer alerting me when it is time to reload the boiler with fuel.

    I actually enjoy the tinkering and daily loading of the boiler. Have considered storage but actually think I might get bored only building a fire once or twice a day if that. In addition, what if your burn time for the storage capacity is say 3 hours and you miscalculate and add too much fuel after your storage is at setpoint? Would you not idle then for say the next 12-24 hours? Just trying to decide if storage is all that it is cut out to be and if for some maybe it is not the best strategy. Any thoughts?

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  2. I've been burning for a year without storage. Just cleaned the boiler and no creosote. Just a fine coating of ash on everything. I'm adding storage mainly for convenience. I burn pine and need to reload at 5 am on really cold nights. Hopefully storage will allow me to get through the nights without reloading.

    As far as idleing if storage is up to temp and I overload the boiler my piping will send the water from the boiler to heat the house and not draw from storage until the fire is out. So no more ideling than without storage. And probably a lot less.
  3. KenLockett

    KenLockett Member

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    On those cold nights when you have to reload at 5am, at what time in the evening do you make your final load and do you fill the firebox to the brim? Would seem in your case as with me no issues with idling and that storage would be simply for convenience. If I did put storage in I would plumb it so I could run in a bypass mode to storage if I so chose. Again, not sure if the investment cost of the storage in my case is worth the return. In your case are you unable to find hardwood for longer burns? To me seems cheaper at least in the short term to invest in purchasing quantities of hardwood versus adding storage. I for one am short on additional real-estate for the storage tanks and am not even absolutely sure how I would get them into the basement assuming long length. Had a bear of a time getting the boiler in.
  4. maple1

    maple1 Minister of Fire

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    I think storage is more about convenience than anything else - but I also think it adds to efficiency if the boiler can burn unrestricted until the fuel is gone.

    After living with my old unit for 17 years and having to either get up early to re-load with wood, live with a cold house in the mornings if I didn't get up early, or listen to the oil burner sending money out my flue if I didn't want either - having a warm house 24/7 with only having to tend to the boiler in the evenings is priceless. Throw in the ability to make it through a couple of days in the winter with no fire (with proper planning) when nobody is home - even more priceless.

    Add in the reduced wood consumption I'm pretty sure I'm seeing and I'm sold on the benefits of storage.

    Having said all that, I would also agree that it is not always 'the best strategy', depending on ones personal situation & preferences - as can be seen by all the various heating system layouts being used quite happily by everyone on here.
    woodsmaster and KenLockett like this.
  5. Fred61

    Fred61 Minister of Fire

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    I run with storage and build one new fire a day. My boiler will idle for about 10 munutes once during the charging of the tank, usually toward the end of the burn when tank temperatures approach boiler temps. Usually by then the fire is mostly all charcoal and doesn't deposit much tar on the fire chamber walls. My walls are not shiny but are coated with a dry crumbly black coating. I don't know if it means anything or not but I became a little gun shy about that shiny surface. It looks like wet tar and that's what the firebox looked like on my Wood Gun which started weeping water through the walls in 8 years.

  6. On cold nights (10* or so) I fill the boiler at 10. Fire will be out by 5 but the house is still warm. On below zero nights I use some hardwood. 90 % of what I burn is pine that a tree service drops off already cut to length. I have to cut my own trees if I want hardwood, just takes me more time. It is much easier for me to use the free pine.

    I also find on many sunny winter days that I'm waiting untill 5 or later to start a fire since I have good solar gain. I have to judge the wood load right or I can't reload at ten when I want to go to bed. Storage will allow me to load the boiler up at more convenient times of the day.
  7. heaterman

    heaterman Minister of Fire

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    From what I hear, the latest emission testing has revealed that the outdoor gassers and even top notch indoor gassers get quite "dirty" when idling and coming out of an idle period. The powers that be are now talking about minimum size storage capacity for all gasification units with pellet burners being a possible exception. This is due to the fact they can shut down with an empty fuel chamber with each cycle. We will be hearing more about this in the future I'm sure.
    Idling is something to be avoided.
  8. That doesn't sound good for future wood gunners that don't want to use storage.
  9. KenLockett

    KenLockett Member

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    Heaterman, my gasser unit is 140K BTU output and my heating load based upon baseboard length is roughly 65K BTU and not sure about my indirect hot water heater adds. What do you think the minimum size storage capacity I could go with is? I have seen on here storage as little as 400 gallons and as high as 1000 gallons. Water capacity of my boiler is approximately 50 gallons. Do you think adding as little as 200 gallons of simple storage would even be worthwhile or is there some magical minimum number that yields reasonable return on investment.
  10. avc8130

    avc8130 Minister of Fire

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    Maybe Wood Gun will lobby.

    I'd be more concerned with a carte blanche ban on wood burners. That is essentially what happened to the outdoor guys. Before the outdoor gassifiers could even make it, many towns banned OWBs altogether.

    ac
  11. Fred61

    Fred61 Minister of Fire

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    I'm no expert but I do have some experience with no storage, 200 gallon storage and 500 gallon on my 85000 btu unit. Even with my little boiler, 200 gallons is like no storage. A waste of time and money. With 140,000 btu I would recommend 1000 gallons. 500 gallons is still borderline for me with my unit and I have a real light heat load. I know it's expensive, a pain in the you know what to install and a gross piece of hardware to be looking at for the duration but once you experience the benefits, which won't take long, you'll overlook all the negatives.
  12. KenLockett

    KenLockett Member

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    I'm sure those of us without storage would be grandfathered in and not be subject to new regulations. There are regulations pending for outdoor wood boilers in NY state but pre-installed units are exempt, or so I've heard. I'm sure if the radical environmentalists had their way we'd all be heating with electric!
  13. Fred61

    Fred61 Minister of Fire

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    As long as it's not generated with coal, oil, wind, nuclear or those damn hydroelectric dams.
  14. KenLockett

    KenLockett Member

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    'Tis the irony I suppose
  15. Tennman

    Tennman Minister of Fire

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    Ken, now in my 4th season I've finally gotten to the point of having well seasoned wood and I'm amazed at how much excess energy we now have. In previous years the boiler struggled to keep up with the demand, but regardless of temp this year it's easily staying ahead. Consequently lots of idling now which we only saw when it was mild outside. Before I thot storage would be nice but now I see I need it.
  16. Nofossil

    Nofossil Moderator Emeritus

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    I ran my first year without storage. I was pretty careful about loading, did lots of small fires, and let the house temp fluctuate quite a bit. The boiler was clean at the end - no creosote.

    I can't say that I've seen an increase in efficiency after adding storage, but there's a HUGE increase in convenience. I'm skipping a day right now - third time this week. For me storage lets me build a fire when it's convenient for me, and allows me to maintain much more even house temperatures.
  17. That is pretty much how I've been running my boiler with out storage. And how I hope to run it with storage.
  18. heaterman

    heaterman Minister of Fire

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    ........and only when the wind was blowing or the sun was shining.
  19. heaterman

    heaterman Minister of Fire

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    Storage should be of enough capacity to absorb the heat from an entire load of wood from whatever boiler you are burning. A rough rule of thumb would be that 100# of seasoned wood can generate about 735,000 btu's @ an efficiency of 70%. Considering that factor would be a good place to start in sizing your storage. If your boiler holds 50# size to that, if it holds 100# size to that.
    The next thing to consider is the temperature swing you can live with. Can you run your storage from 130 up to 180* or do you have to stay at 160* and up. The heating systems ability to use lower temp water will be a big factor in the sizing question also.
    For example; if you used the 100# scenario and needed to bank 735,000 btu, the storage capacity would have to be twice as big with a 20 degree diff as it would a 40*.

    Other factors to consider would be the heat loss of the building and how often you wish to load the boiler.
  20. jebatty

    jebatty Minister of Fire

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    Heaterman, I think this is over-stating the btu's from a load of wood. My research shows that one pound of wood at 20% MC and 400F stack temperature will generate about 6,050 btu's, or 100 lbs will generate 605,000 btu's. A change of 100F in stack temperature will result in about a 2-3% change in btu's, so that 300F stack temperature and 100 lbs of wood results in about 623,000 btu's, and 500F stack temperature about 587,000 btu's. Energy in Wood

    Next is a reduction resulting from the inefficiency of the boiler in transferring that energy to the system. These inefficiencies result from losses through the boiler skin, piping, storage tank, etc. For my Tarm, using the 6,050 btu/lb, and measuring the increase in water temperature in my well insulated 1000 gal storage tank, the efficiency is about 81%. So, 100 lbs of wood results in btu increase in 1,000 gal of storage of 490,050 btu's, which is a 59F rise in temperature; or 1.7 lb of wood will raise the tank temperature 1F.

    I load my Tarm based on the degrees I want to raise the temperature in my storage tank. If the storage tank average temperature (determined by 3 sensors on the tank with digital read-outs), is 120F, and I want to raise the temperature to 190F (+70F), I weigh out and burn 1.7 x 70 lbs of wood = 119 lbs. I burn mostly pine and some aspen, and that then results in 2-3 loads of wood over a 4-6 hour period. My storage tank is located right next to the Tarm, a 15-58 is the circulator whose only function is to load storage from the Tarm, and flow rate is about 14gpm on HI. This burn method results in charging the tank as determined with no idling, because as the last load burns down and delta-T closes, btu output from the Tarm also is falling so that all output is being transferred to storage.

    I agree completely with nofo's experience, and in my case I only need build a fire at most every other day and at a time that is convenient. The number of times a fire needs to be built is of course based on the heat load to be satisfied, and my experience is related to heating my 1500 sq ft shop, well insulated, and maintaining an in-floor radiant temperature of 61F. In my case the Tarm and storage also is located my shop, so nearly all system heat losses also heat the shop. Based on my calculations in this situation the overall efficiency of my system is raised from about 81% to 89%.

    Although I can't say I've seen (or measured) an increase in efficiency from storage, logic tells me that the efficiency has increased due at least to fewer boiler initial start up times and idle shut-down and re-start times. I believe a fire is least efficient in converting the fuel to energy during these times, and that the most efficient fire in a gasification boiler is when the fire is allowed to burn at the maximum rate based on the design of the boiler.

    Happy Holidays to all.
  21. KenLockett

    KenLockett Member

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    Tennman, in your case, you're keeping up with demand with excess energy and subsequently have lots of idling. My point is that what is the problem with the idling as long as there is no creosote formation. Plenty say no gain in efficiency with the storage. Only reason I can see for the storage assuming there is no creosote formation is convenience. If your objective is not convenience then why do you say you need it? Not trying to be critical just trying to understand your reasoning.
  22. KenLockett

    KenLockett Member

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    Over the past 24 hour period, I have run approximately 10 firing/idle cycles, and my total firing time was approximately 900 minutes and my approximate idle time was 540 minutes. Outside temps were 30-38 degF so not even close to the coldest nights. Would expect the ratio of firing to idling to increase with colder temps. Not building super large fires at this time but that does not bother me. Any thoughts from anyone on this ratio? Too large, Too small? Would assume this is typical for the past year although only now able to measure times with the PLC and temperature controller.

    By the way, house temps for non-setback areas remain consistent during this period at 72 Deg with no observable swing (i.e. downstairs 68, upstairs 72 during night and downstairs 72, upstairs 68 during day). I run two heating zones.

    By the way, can get a 8-12 hour burn depending on outside temps with full load of wood (5.1 Cu Ft firebox). Don't normally fully load other than when very cold outside.
  23. maple1

    maple1 Minister of Fire

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    The past couple of weeks, I've only had one firing cycle every day. My boiler does not idle. My firebox holds 3 cu.ft., I've ben starting with just under a full firebox (with lots of airspace for firebuilding), then topping up if necessary about 3 hours later - so I think between 4 & 5 fu.ft./day.

    There has to be an efficiency gain in going from 10 firing cycles to just one. Every one of those cycles has some start up smoke, and things (chimney & refractory) have to get hottened up again for full burn efficiency each time.

    I haven't seen any good data that really shows increased efficiency with storage on here, but my seat of pants is saying there has to be some?
    Taylor Sutherland and Fred61 like this.
  24. Nofossil

    Nofossil Moderator Emeritus

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    I believe that there has to be some efficiency gain as well. Certainly there would be if you burned without storage by loading up to the gills and then letting it idle.

    However, data doesn't generally lie. I haven't seen data from my own (highly instrumented) experience or from anyone else that quantifies a measurable improvement from running a gasifier efficiently without storage, to running it with storage. I'm still a big fan of storage - wouldn't want to give it up, but if you're already minimizing idle time I wouldn't suggest that you cut less firewood based on adding storage ;-)
  25. KenLockett

    KenLockett Member

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    I agree that perhaps there is some efficiency gain. I'm just suggesting that overall it may be so little to be negligible and not warrant the monetary investment required for installation of storage. I can see the benefits of storage relative to convenience depending on how much time one has to 'tinker' and load firewood for heating purposes. I think my main concern relative to the idling periods is am I creating creosote and/or operating the appliance in such a manner that might reduce the life of the unit.

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