Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: netwerx-r-us on January 15, 2014, 08:58:57 PM
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Anyone have any knowledge around using a large storage tank tied into a outdoor boiler to store your heat for later ie all night ?been reading a few sites and they claim that the boiler will only work 6-7 hours and then store that heat ? anyone have any experience in this , here is one site http://slatevalleyboilers.com/index_files/Heat_Storage_Tanks.htm (http://slatevalleyboilers.com/index_files/Heat_Storage_Tanks.htm)
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I personally do not use/have a large storage/buffer tank, in my system. So please take everything I say with a grain of salt.
Assuming that your stove is correctly sized (BTU rating) you should be able to keep a fire/warm water all night. When fired correctly evern on COLDEST day (recently -20's, with windchill -60) I was only firing 3 times a day:
1) Once at night before bed, loader up good
2) Morning, probably 1/4 to 1/3 full, just to keep bed of coals and to help restart fire
3) Lunch time, probably 1/3 to 1/2 full, enought to get me to night
Also, how much heat loss in that large storage tank have and since it does store energy (say 200k btu like that article stated) that mean that the first 200k Btu the boiler makes during a burn will go straight toward warming the storage tank back up and not heating the house. So yes it may be great to have a storage/backup plan you should also think about how it will affect burn/recovery time on boiler.
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Storage tanks on OWB's or any stove for that matter do not create BTU's, they only store them, you can certainly extend the burn times at night but you first must create the BTU's during the day. A good application for storage would be a greenhouse that uses very little heat during the day so more heat can be dumped into the tank, this keeps the boiler running hot in daytime and then those BTU's can be used to supplement at night when there is a huge demand on the system
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I haven't tried this because my setup has plenty of storage but I did read an interesting article in Mother Earth News about it.
They were setting their system up based on solar power an built a storage tank on the cheap.
You can source all parts from your local building supply company and build it yourself.
If you're interested I can copy the post tomorrow and post it.
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Slim is tellin ya where the only advantage is.
More water does not equal more efficiency.
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I can see this working in a greenhouse like Slim said or maybe if you have the tank in a basement under your living area, for me in a slab home I don't think there would be a good place to put it and outside in winter would seem like you're wasting any advantage.
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Some of those super efficient indoor boilers use a large storage tank, One big burn and then it is done for a few days. My friend has one but they are really expensive he paid 30g installed. So disagreeing with some thoughts there is a benefit to one long burn verses a lot of firings your temps are at maximum efficiency for gassification. You also get the freedom of being able to go away for a few days and your house wont freeze. So initially you will have to shovel the wood in to get the tank up to temp once you are there it will not be as bad next time it cycles. I am in the process of building one and it should be done by middle of march. I do not have a gassifier so I may not have any great efficiency gains but the ability to leave for 3-4 days without worry or bothering someone is worth the cost to me.
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Batch burn units arent compared to owb though. A long burn can be most efficient. I know folks with garns who have spent 25k or more and still fire everyday and sometimes twice in cold weather with 2000 gallons. One bad thing is if you let it get to cool before you refire then one batch wont bring it back up to temp, so instead of throwing wood in and going on about there day, they have to stick around to throw in another batch.
With 2000 gallons and 50 degrees worth of drop
16,600 pounds of water. 200 degree down to 150 is 830,000 btu.
Conventional stove may get 50 percent of btu available, thats being generous
So. Wood is 8600 btu per pound. Moisture content pets say is .25. 6450 available btu, a conventional stove may claim half those, so 3225 btu per pound of wood.
It would take 257 pounds of wood to acheive that 830k available btu
With 830k btu your heat loads would look like this. If your heat load was 69kbtu per hour youd last 12 hour
if it was 34,500 youd go 24 hours. 48 hours on 830k would only be 17000 btu per hour
Soo... Youve either gotta have far more than 2000 gallons pf storage or this 3-4 days stuff aint gonna happen.
At 2000 gallons with 50 degree drop, 96 hours would only provide you with 8500 btu per hour
I know there is more heat available than simply 200 down to 150
But once you go below 150 your ability to heat watrr through an exchanger drops significantly as well as performance
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I've noticed with my setup once it gets below 150 degrees it takes alot longer to get from say 120-150
than from 150-180.
I'm not sure but I believe when water gets this cold the stove condensates up to 145-150.
Once I reach 150 it takes off.
700 gallons lasts me 12hrs in most cases. If it's below 25 degrees I have to load my box (2) times
per day. My firebox is alot smaller (15cuft) than most, if burns up completely if I allow it to go down to
120 then get it to temp 180.
I should use alot less wood next year because I'm insulating my shop (where it's located).
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Fryedaddy, where you located?!
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All I know is my stove has been recovering way faster at 165-180 vs 150-165.
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thanks all , very good info to think on , I do heat 2 large greenhouses and I,m leaning towards a solar water heating ( thermosyphon or pump) , but a storage tank in ground to store whats collected during the day and run off at night , i was inquiring about feasibility to tie in to boiler but i think Someone said it , i still have to heat that water to begin with so i don't think there's much advantage there , But a solar system with no moving parts might be a wise investment ,home made on builditsolar, thanks again
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Netwerx, that is one of those places that it works very well, are you in Dairy country, old milk tanks make great storage tanks, I'd like to talk more about it.
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Scott,
I'm in N.C. "Foothills", doesn't get as cold as most of you guy's
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Netwurx,
FYI, I can gain heat with my solar panels on a 36 degree day, my stove was around 150 degrees with full sun.
I have (6) panels but you would need alot more for greenhouses, plus storage.
If you look around you can find the panels fairly cheap. I'd also look into old cast iron heaters as well. They would
allow you to realize the heat better, depending on the setup, just my belief.
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Fact, boilers are at their least efficiency while idling. The best OWB's also have the largest volume or storage of water. Any boiler system will see a net gain by adding any amount of storage, if installed correctly. Anytime you increase the gasification burn time, you increase the total efficiency. Who would run a delta T of 50 on storage. One giant loop hitting 2-4 exchangers is not correct. Even those mod cons use buffer tanks to increase efficiency.
I don't know about that math, but if a 125kbtu tiny boiler can recover heat for 1500-2000 gallons and not fire for 2 days while heating 3500sqft, I think a larger boiler with more mass can also. Both being gassifiers. Some are getting more days. You have to think of your storage as you trucks gas tank, you don't have to top it off to operate. And with outdoor reset controls and the Taco electronic ODR or set point mixing valves you can see a week easy without firing. Over in Europe its illegal to idle, and the boiler controls don't even have that option, over here at least you can. If you understand how a buffer tank or hydraulic separator works then you can see how you can recover storage and cover a heat demand at the same time.
Proper placement and control of BTU's make a system efficient. My storage tank looses 1/2 degree per hour or 12 degrees per day. With the cover its 7/day. Most of it is thru the pipes themselves that don't have gravity loops.
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Slim , Dairy country , no , I'm about 60 miles west of Nashville tn , Its 19 degrees now , 2 large greenhouses are very inefficient to heat , I keep them at 55 and 60 degrees each , I get about a 6-7 hour burn time when its this cold , the greenhouses do heat up during the day simply from the sun but have no way of storing that heat gain , Scott's post made sense , it can be done but if after you get that much water to temp if you let it go down it will be a hard time keeping up, I see that with my 300 gallons , i can only imagine with an additional 500-1000 gallons tied to it .
I think I will look at using the sun with some homemade solar collectors and a water storage tank underground in the greenhouse , after a bit of research I see dairy tanks and even propane tanks being used , I think ill build me a tank below grade and insulated to give it a whirl, like everything else I have 15 projects going on at same time
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Netwerx, another good place to look for tanks is retired fire trucks, the tanks are normally plastic and almost never re-used, think about bench heating at night off the tanks, alot less heat loss and the plants won't know the difference!
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Fact, boilers are at their least efficiency while idling. The best OWB's also have the largest volume or storage of water. Any boiler system will see a net gain by adding any amount of storage, if installed correctly. Anytime you increase the gasification burn time, you increase the total efficiency. Who would run a delta T of 50 on storage. One giant loop hitting 2-4 exchangers is not correct. Even those mod cons use buffer tanks to increase efficiency.
I don't know about that math, but if a 125kbtu tiny boiler can recover heat for 1500-2000 gallons and not fire for 2 days while heating 3500sqft, I think a larger boiler with more mass can also. Both being gassifiers. Some are getting more days. You have to think of your storage as you trucks gas tank, you don't have to top it off to operate. And with outdoor reset controls and the Taco electronic ODR or set point mixing valves you can see a week easy without firing. Over in Europe its illegal to idle, and the boiler controls don't even have that option, over here at least you can. If you understand how a buffer tank or hydraulic separator works then you can see how you can recover storage and cover a heat demand at the same time
Proper placement and control of BTU's make a system efficient. My storage tank looses 1/2 degree per hour or 12 degrees per day. With the cover its 7/day. Most of it is thru the pipes themselves that don't have gravity loops.
not quite sure what your reffering to as a delta t, shew. Im talking available affect heating temp of water not difference in supply and return
No one is arguing that a long burn time is less efficient, but to think you can take a conventional stove or even a gasser not designed for storage and add storage and suddenly heat for days per fill isnt true either. The math is where its at, there is only so much usuable heat in 2000 gallons of water. I was simply saying if it cools to 150 from 200, thats still 830k btu of available heat. So if your heat load is normal for most folks lets say 45kbtu per hour, just divide 830/45 and you have how many hours it will do its job.
Once again, I know the European style mass storage boilers who do batch burns are very efficient, but in an outdoor wood boiler forum its not practical or a good idea to lead people to believe the answer to there efficiency is nore storage. Best advice is for everyone to install there stoves aa close to dealer specs as you can, it was designed that way for a reason
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A boiler is a boiler, regardless of fuel or efficiency in burn or transfer. Any storage, be it buffer tank or storage tank is exactly like a battery. Delta T, well you don't run a battery dead before you recharge, and that's what you'd be doing by having a big delta T in tank temps. All these OWB's already are fed multiple times a day. So while tending why not run at max efficiency to recharge. So if it takes a solid 2-6 hours of full gasification (a stoves most efficient use of wood) to recharge storage it reduces cycle times. Just with any boiler the more you reduce cycling the more efficiency you get out of the boiler and fuel.
Even something as small as a 30 gallon buffer tank will help. A lot of the problem lies with typical bad manufacture design and suggested install. Just like the diagram where you see everything connected in one big loop and an oversized pump on too small of a supply line running 24/7. There is nothing efficient about a wood eating design like that.
2000 gal is a lot and that's why there's design sizing programs to fit the bill. But as the industry likes to do, bigger must always be better.
So when a OWB is flowing 8gpm thru 1" on a call, but only the baseboard or air handler is calling for 30-50kbtu or 3-5gpm flow, the buffer or storage tank would store the excess. Every so many calls the boiler wouldn't even have to fire. saving fuel and electricity from a proper design and placement of btu. Buffers and storage are a proven design in hydronic heating, utilized by the most efficient systems. The heating source does NOT matter. The OWB industry itself makes its own bad name, by letting butchers install their product. This does not apply to all manufacturers and installers. I am sure you yourself have taken some bad installs and made a very good system out of it. Half or more of the ones I work on, are flat out jokes. Where they sold him the cheapest package to make the sale, rather than doing a proper sized design, of course it cost more to do it right. Pay a little now or pay a lot later. Unfortunately it's the customer that suffers. Zoning, buffer, correct circs and supply line size and quality are where most problems lie. It is easily possible to cut wood usage by 20% Really bad ones can cut the wood in half. 1% of the time an OWB installer supplies the customer with a manual J.
The only way a buffer or storage would not benefit a system is if the output perfectly matched the load on every call for heat. An impossible feat for even the most flexible and efficient systems, when the correct design is sized for the coldest day.
In your opinion what percentage of OWB installs are done correct? Doesn't have to the best, just working properly
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1820 sq/ft house up in Almont, plus the man cave poker room / shop office. OWB rated at 120kbtu/hr max , 1000 gal LP tank feeding the primary loop thru a hydraulic separator and a taco i125T4R-1 mixing valve that feeds baseboard zones ,infloor tile heat and IDWH in the house. He burns from 6 to 7-7:30 charging the storage, while guys show up for work and getting the tree trucks warmed up. Then again in the evening for an hour to 2 hours charging the storage. That's it , no feeding during the day or late into the night, when it's above 25 degrees for the day it only takes a 40 minute burn to recover. The house heat loss is 39,000. The shop office ??? Its 11x 22' corner section of the barn not heated at night unless we're playing poker.
Prior to the storage, added pex lines and ODR mixing valve it burned or idled 24/7 and had to be fed minimum 3 times/day packed and praying for no bridging. It doesn't have to be packed full and it only burns hot, no low return temp worries. The fire box is much cleaner from the hot burns.