For those running without storage - never stop (re)thinking
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Thanks for the link to the side-by-side study, DVD. I agree that it's intuitive that setback should save at least some fuel, but it's still interesting to read about the results of a controlled experiment. Pellets sound more like fossil fuel boilers in terms of gaining from t-stat setback. With the capability to auto-feed just the right amount of fuel, it's easy to imagine how pellets can get the same setback benefit as with an oil or propane boiler. And for the folks who gain from setback with wood boilers, every system is different. My 150 is a slight bit over-sized for the design day load, and that translates to way over-sized on milder days. So filling the boiler with more wood at bedtime is a complete mismatch to reducing the heating load via setback. Ihookem, you're focused on the amount of wood used, which is definitely #1 for most folks. My big issue with idling is the possibility of creosote forming in the boiler HX tubes (problems with this a couple of years ago). I've seen an amazing reduction in creosote (using the door as a barometer), as a result of no setback/much less idling. The bonus in my case turns out to be less wood used - same amount at night and nothing extra needed for recovery in the am. What we need is an auto-feed wood boiler, where a conveyor sends in a split, as needed, maintaining a right-sized fire. I'll go back to doing setback when one of those comes along ;-)
And that's why I get creosote in the morning. The only thing left to do is put small pieces in and run it hard to clean the box out and get the house back to temps a little faster. Does anyone think creosote takes a toll on a boiler? I think it does to some degree but I always have a hot boiler. I also think a hot boiler will last longer than a boiler going from cold to real hot to cold almost daily. What do the rest here think? Also, I asked about how long boiler lasts. Any stories on how long they last and how they were used?
A thin hard layer of creosote in the primary chamber is normal and expected, and many feel that it actually seals and protects the steel from corrosion. But when too much accumulates on the door, it can become a problem for the gasket. It would be unusual for any quantity of creosote from a gasser to make it into the flue, but the "hidden" location for creosote formation is the boiler HX tubes. Again, a hard creosote layer in the tubes probably isn't going to do any permanent damage to the boiler, but it does impact the efficiency by reducing the heat transfer of the HX. If the tubes are never cleaned, it may also be possible for one or more to become completely blocked with accumulated creosote. I noticed that you posted today in another thread dealing with this issue, and would recommend (since you have a lot of idling) that you pull the top plate of your boiler and check the tubes for creosote. I speak from experience on this :sick:ihookem said:
Thanks Workforwood,do I get to the top plates by taking off the left side panel? I do have the super so I can clean the tubes but it sounds like stuff still needs to be cleaned in there.
I don't have an EKO, and can't give you the exact details on getting at the HX tubes in your boiler. Maybe another 25 owner will jump in and provide the specs for you.
There are times when setback does work with radiant. We have a customer with a 3000 sq ft shop - 17' ceilings - all radiant slab. The system is hooked to 1000 gallons thermal storage. (along with a house -forced air - and 24 x 24 boiler shed with radiant slab) The slab in the shop gets a 5° setback at night... This creates a flywheel effect, allowing the wood boiler some free time in the evening to stack some 180 or 190° water in the tanks for the overnight cycle. The trick is to time the setback so things get back up to temp when he needs it, as well as making sure there is always available heat at the top of his tanks for the house. This works well because we have storage set up that is able to carry the entire load that is induced when the slab comes online - a load that the boiler could never carry on it's own when the thermostat comes out of setback. We also keep the water temps up close to maximum through the slab (around 124) to make it react to the setback more quickly when the thermostat calls for heat.
The biggest reason that people tend to use setback along with their gasifier is to keep the fire from going completely out overnight. It's much nicer to throw wood in on top of some coals than it is to start from scratch, even at the expense of some additional idling. One of the issues I think people face though with an idling wood boiler is their draft. If you're getting too much air through the boiler in idle, you're going to produce additional creosote. The bottom line is... if you're going to idle, your best to do it for longer cycles in order to produce lower deeper idle states and longer hotter burn states. Its the same idea as using a buffer tank.
I will always agree that short hot fires are the best way to efficiently run a gasifier without storage. Many people, however, want to produce heat 24/7 with their gasifier in order to justify the return on investment, and not have to suffer from the house cooling down in between burns and having to restart the fire all the time from scratch. It's a balancing act for sure, and I suspect everyone will have a little bit different take on what works best for them.
cheers
The biggest reason that people tend to use setback along with their gasifier is to keep the fire from going completely out overnight. It's much nicer to throw wood in on top of some coals than it is to start from scratch, even at the expense of some additional idling. One of the issues I think people face though with an idling wood boiler is their draft. If you're getting too much air through the boiler in idle, you're going to produce additional creosote. The bottom line is... if you're going to idle, your best to do it for longer cycles in order to produce lower deeper idle states and longer hotter burn states. Its the same idea as using a buffer tank.
I will always agree that short hot fires are the best way to efficiently run a gasifier without storage. Many people, however, want to produce heat 24/7 with their gasifier in order to justify the return on investment, and not have to suffer from the house cooling down in between burns and having to restart the fire all the time from scratch. It's a balancing act for sure, and I suspect everyone will have a little bit different take on what works best for them.
cheers
Piker said:
That seems contradictory. A buffer tank should even things out. But you're saying longer off and on cycles is better.
I need more explanation.
I think Piker is saying that : if you can keep longer idle times that the tar is generated in the early stages and when the air is removed for longer period that it will go dormant and make less tar. I am little confused on the 124 slab set back thing. I boils down to GPM x split, the temp is not a variable.[assuming there is sufficient load] More cooler water will work as fast has less hotter water and if thanks are low then more cooler water available. I know every one is different.
My 32 x 48 radiant slab, 6 loops of 1/2" pex, is supplied with 100-105F water, slab sensor is set at 61F, 1F differential, and typically delta-T = 30F +/-. The flow meters on the manifold show 0.5 gal/loop, 3 gpm total. That works out to 45,000 btuh. Typical run time on the slab circ is 2 hours 20 minutes +/-, which is 105,000 btu's. The slab is heated from storage, and storage temp drops right around 12-13F on each cycle, which also (the miracles of data collection and math) is 100,000 - 108,000 btu's.
Time between heat cycles (start of one cycle to start of next cycle) varies a little based on outside temp, but based on my last data set and outside temps +5 to +25F, the cycle times were right around 8-9 hours, which is about 13,000 btuh heat load.
This use would present a difficult operating scenario if there was no storage. My Tarm, at 140,000 btu rating, averages less than that, but fully meets slab heat demand plus excess to storage during burns. Firing the Tarm for only a 2-3 hour burn, and then off for about 5 hours, would mean refiring the boiler each cycle. With storage, however, I am refiring only every 2-3 days, burns about 6 hours each (pine slab wood).
I don't use setback on the slab. At 61F inside air temp ranges between 55-60F, which is very comfortable, shirt-sleeve working conditions.
Time between heat cycles (start of one cycle to start of next cycle) varies a little based on outside temp, but based on my last data set and outside temps +5 to +25F, the cycle times were right around 8-9 hours, which is about 13,000 btuh heat load.
This use would present a difficult operating scenario if there was no storage. My Tarm, at 140,000 btu rating, averages less than that, but fully meets slab heat demand plus excess to storage during burns. Firing the Tarm for only a 2-3 hour burn, and then off for about 5 hours, would mean refiring the boiler each cycle. With storage, however, I am refiring only every 2-3 days, burns about 6 hours each (pine slab wood).
I don't use setback on the slab. At 61F inside air temp ranges between 55-60F, which is very comfortable, shirt-sleeve working conditions.
ISeeDeadBTUs said:
Gasifiers are at their least efficient when they smoke. They tend to smoke the most right at the points where the draft fan turns on before the coals and refractory are up to temp, and then again immediately after the fan turns off. By allowing the cycle times between fan on/fan off to be extended, you create a situation of higher highs and lower lows with less short cycling. This can be achieved by using some additional water volume on the system in the form of a buffer... or using a setback at night to allow the boiler to reach a very low state of idle where things cool down and minimal gas is escaping out the stack... when the temp comes back up again, the boiler has to work harder and longer to produce the required heat load, and thus a hotter burn and better secondary combustion is achieved.
I am not saying that idling is the best case scenario...
cheers
bigburner said:
We are not setting back the temperature of the slab... only the thermostat for the building. The higher water temps in the slab will transfer more btu's/hr into the slab than cooler water say at 80 or 90°. (130° is about the max you want to go into concrete) This is to allow a faster recovery of the temperature inside the building after the setback is removed. We have been running the building at 50° with a 5° setback at night... so far so good... though some more expiramentation might yield other scenarios that would work as well.
cheers
musclecar joe said:
joe,
Stretching burn times by an hour or more just by adding a buffer is probably an unrealistic goal. The best analogy I have heard with regards to a buffer tank is to compare it to a large flywheel on an engine. It does not add or subtract energy, just provides inertia to overcome obstacles.
Likewise, a buffer does not add btu's to a system - though it can actually subtract them if you are losing excessive heat through the tank or piping. It also allows you to overcome "obstacles" a little better, such as a mass of cold return water coming from a zone that has been down for a while, and the on the other side, it allows the boiler to fire longer when it fires, and idle longer when it idles. The increase in efficiency that we're talking about is pretty hard to nail down, but more than likely wouldn't be more than a couple points once you factor in transmission losses, etc. Best case scenario, lets say you added 5% efficiency to the system by adding a buffer... you're burn times might increase 30 minutes. The real benefit is probably more in the operation of the boiler itself with regard to creosote production and keeping the unit clean... which, if you think about it... a clean boiler can transfer btus into the water better than a dirty one... and 5% isn't an unrealistic gain from a dirty boiler to a clean one.
cheers
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