Measurable benefit of adding storage to updraft boiler?

[Hydronics]

Has anyone added storage to their updraft boiler after running a season or more without it? How much has wood consumption decreased? How much longer (average) between loadings/firings.
I have a cast iron updraft Buderus in an out building which is a quality unit but obviously never achieves the combustion efficiency of a gasifier. I can currently get 6 to 9 hours burn time with a 1.5 ft3 firebox loading depending upon outdoor temps.
Thanks, Jeff

 

[Nofossil]

I don't have any hard data, but other people's experience might not match your own anyway. The improvement from storage (if any) depends on how you run the boiler. If it spends a lot of time running mostly damped down, then storage would probably help quite a bit. If it tends to run flat out most of the time, then storage will not likely make much difference.

In the gasifier world it's much the same. Some people talk about a huge increase in efficiency with storage. When I ran without storage, I always did short hot full-throttle fires. I saw almost no increase in efficiency when I added storage. Convenience is another story, though....

 

[Hydronics]

Understood, it obviously spends more time idling when outdoor temps are higher, therefore would be most beneficial at warmer temps. Based upon what I observe for wood consumption when idling, I'm not convinced that it's wasting a significant quantity of wood at idle.
When you ran short full throttle fires you must have been always home or allowed the building temps. to swing up and down. When you say convenience you're referring to duration between loadings, correct?

Assuming non-stop burning: the potential efficiency increase in a gasifier with storage is greater than thst in an updraft with storage because the delta in efficiency is (we'll say) 0 vs. 85 for a gasser & 0 vs. 50 for an updraft. I think it's important to note that the tighter the firebox (sealed), the less waste at idle because the negative flue pressure will draw less smoke (unburnt fuel) up the chimney. Another note, in an updraft some of the creosote deposited at idle gets burnt during the next full burn cycle, in a gassifier it's gets deposited in the fuel box & cannot get reused.
Ultimately I want to upgrade to a gasifier, probably with storage, I'm just trying to determine the potential benefit of storage with my updraft.
I've read some of your posts, you're doing things right based upon your wood usage.

 

[Nofossil]

Understood, it obviously spends more time idling when outdoor temps are higher, therefore would be most beneficial at warmer temps. Based upon what I observe for wood consumption when idling, I'm not convinced that it's wasting a significant quantity of wood at idle.
When you ran short full throttle fires you must have been always home or allowed the building temps. to swing up and down. When you say convenience you're referring to duration between loadings, correct?

Assuming non-stop burning: the potential efficiency increase in a gasifier with storage is greater than thst in an updraft with storage because the delta in efficiency is (we'll say) 0 vs. 85 for a gasser & 0 vs. 50 for an updraft. I think it's important to note that the tighter the firebox (sealed), the less waste at idle because the negative flue pressure will draw less smoke (unburnt fuel) up the chimney. Another note, in an updraft some of the creosote deposited at idle gets burnt during the next full burn cycle, in a gassifier it's gets deposited in the fuel box & cannot get reused.
Ultimately I want to upgrade to a gasifier, probably with storage, I'm just trying to determine the potential benefit of storage with my updraft.
I've read some of your posts, you're doing things right based upon your wood usage.

You're absolutely right on all counts. Without storage, you either idle a lot or allow wider temperature swings. You're also right to look for real data on the efficiency benefits in your case. I'm convinced that there's a fair amount of wasted energy at idle even in a traditional boiler, but I don't have the data to prove it.

It's also very true that gasifiers stand to gain more from storage. An idling gasifier is presumably very similar efficiency to an idling conventional boiler, but the full throttle efficiency is much better.

The creosote deposits in the upper chamber of a gasifier seem to be self-limiting. It's not the case that the upper chamber will continue to get smaller and smaller until you can only get one log in....

 

[pybyr]

here's my $0.02++-- making a few assumptions, which I'll try to disclose so you that you and any readers can decide if you agree with them in your circumstances

if your existing updraft boiler can heat your house under coldest conditions, then it is at least big enough, output wise, and most heating professionals do a lot of "rounding up" in such variables, as no one suddenly calls up screaming at them over a about the marginal incremental inefficiency of an over-sized appliance, but people do (rightly) call and scream if it's a cold day, the heating system is runnin' to beat the band, but the house is getting colder inside

and I will assume that no one with the patience to study and tend the fire is home during the day to feed the boiler a carefully measured diet of just enough wood, timed/ spaced right, for the varying weather conditions

based on that set of assumptions, if you are feeding the fire enough wood to keep it going the whole day while people are away at other things, then your boiler _must_ be idling a significant portion of the time, during significant portions of the heating season, in order to not be delivering too much heat to the heated space.

whenever you are idling, and for the % of the time your are idling, your next efficiency is at or near 0% whether you're sitting at the red light and idling in a sedan (non-gasifier) or a sports-car (gasifier)

all combustion appliances take a big dive in overall seasonal efficiency (compared to steady-state continuous test efficiency) when being put through varying on-off cycles that go with the territory of the real world - it's just that solid-fuel appliances (other than pellet devices) take a particularly big dive in this regard, because you cannot turn the fuel off once it is lit and while it is burning, you can only put the burn into a really inefficient idle until you can revive it.

someone could develop some really interesting and sophisticated models of how much storage will benefit different people depending upon given locations' peak and average BTU demand, and how much of the overall heating season time an appliance sized for peak demand will spend idling, without storage, in order to be ready to respond, when heat is needed, during times of the heating season when there will never be a need for peak BTUS output (which means the vast portion of the time). My former English teachers would beat me with a stick for the last sentence, but hopefully the concepts got through...

then they could add a parameter to the models that allowed a person to plug in the "full bore non stop burn full tilt boogie" efficiencies of various potential combustion appliances.

then they could add a "switch" to the model to see how the variables run with and without storage of varying BTU capacities (after allowing for some significant intervention of of entropy in the process of cycling the BTUS into and out of storage).

Unfortunately, that someone (to make and refine such models) is not me - math class was not my aptitude; I do well with the concepts but poorly at turning them into numerical practice

 

[cguida]

my 2 cents on this subject... more 'aspirational' than factual, -- but here goes...

I am in your position -- an old up-draft wood boiler (Memco 100). We've used it for several years without storage. It works, but you have to keep putting wood in it (Surprise, Surprise). The fire gets hot, and water temperature goes up, and we have more heat than we need at the moment... only to feel a chill (or worse -- hear the oil burner come on) 2 or 3 hours later. At 3 in the morning, this is an annoyance.

So this year we installed storage -- nominal 1000 gallons. We don't expect to actually save wood this way, although we might get some modest thermal efficiency by burning hotter fires and letting them just go out. But we do expect to gain something in convenience and comfort, and we hope for a significant improvement in 'financial efficiency,' as follows.

Tree length hardwood around here costs about 100 bucks a cord. We might go through 10 cord in a winter, which is a thousand bucks (!). At the same time, we have all kinds of junk softwood within sight of the house. All we have to do is go out and get it. Junk wood usually means a lot of stove loading, and a lot of creosote. Our hope is that with the storage, we can safely burn hot, short junk wood fires at our own convience, and store the surplus heat in the tank for use at 3am. So far (not much data or experience), it seems to be working out that way. House is warm when we wake up.

So if we can cut our expensive-hardwood consumption in half, and replace the BTUs with a cheaper ('free') alternative, then the tank will be worth it. We don't expect to save wood, but we might save some money.

Everybody's circumstances are different. If your boiler goes well all night, and high-quality wood is cheap (or 'free'), you might not experience much improvement with storage -- except maybe for hot water in the summer time. But for us, so far we like it.

 

[Hydronics]

Smee,
Truck length hardwood is $100/cord here also.
You mentioned only getting 3 hrs. burn, what are the firebox dimensions? Mine holds 1.5 ft3 & burns about 7 hrs. on the coldest nights.
Could you give more info. on your setup? s.f.? Insulation? How long can you go between firings now with the storage? Did you make the storage tank/ system?
Encouraging, please keep me abreast on your progress/experience.

 

[Bad Wolf]

Hydronics
Who are you getting your wood from? I'm in Colchester and I'll be looking for truck length wood come this spring.

As for storage, I have a new Tarm and 1200 gallons unpressurized storage and on the coldest nights when its 14* overnight (like this past Sunday) I fire it once in the morning and once in the evening and load it up just before bed. Plenty of heat. On warmer days (like today) I skip the morning burn. I built my tank myself with lots of insulation, look for my post for a $595 tank.
This supplies my DHW as well, which is a side benefit.

 

[Hydronics]

Greg,
I'm in Willington, I'll send you the contacts tomorrow, I have them @ work.
Did you ever operate the Tarm without the storage? If so, did you burn steady? Burn times?

 

[Bad Wolf]

No, I had storage from day one. Since it heats my DHW the wife kinda wanted that as soon or sooner than the furnace. My first ten hours did nothing but heat the tank.

 

[Hydronics]

Greg,
How did you determine that 1200 gallons was the appropriate volume? Tarm's recommendation based upon boiler output?

 

[Bad Wolf]

1200 gallons was the biggest tank I could get in the space I had. That and listening to the folks on the board here that up to a point "bigger was better"

 

[LarryD]

Greg,

How are things going? Did you ever get the low water shut off issue squared away?

What temp do you run your tank down to? What is the highest temps you've gotten into your tank and how long did that take? I am interested because you have the excell 2000 and 300 gals more storage than I have. I wonder how much difference there really is between the two units

 

[Bad Wolf]

The building inspector didn't seem to feel there was any rush. I found a couple of TACO units that I think I'll put in one of the back top ports thats not being used.

The unit is running well, I've really started to get a feel for when and how much to fire it.

The highest that I've seen was 172 at the top. It may have gone higher but I wasn't around to see it. I let it run down as low as 140 at the top, which is around 127 at the bottom. After that my DHW is in jeopardy. It takes about an hour for 10 degrees if no one is calling for heat. Most of my heating is done after 10 pm when the thermostat's drop down. Depending on how far I have to go I'll fill the firebox accordingly.

If I have a really good fire going I reach the high limit and idle about 10% of the time. If I had the bigger unit I think it would just idle more. I probably need more coil area in the tank so I might do that in the spring. Then again I probably won't since it doesn't happen that often.