How much storage is too much

The question might be answered by "what do you want your storage to do that the 1250 will not do?"

I have a 40kw Tarm and 1000 gal of storage. This is more than is needed to serve as a buffer to make sure my Tarm doesn't idle, and the purpose is to provide stored heat to increase the time between boiler firings. My demand during the coldest of winter is around 17,000 btuh, and 350,000 - 400,000 btu/day, and of course less in milder weather. Typically I get at least two days between firings (about 6 hours of burning). That works well for me. More storage would mean longer times between firing but also longer periods of firing and tending the Tarm. My storage is in the heated space, so heat loss from storage also heats my shop, and heat loss therefore is a non-issue. Any large increase in storage for me would not be very practical, although it would allow me to be absent for longer periods without any need for backup heat. That need is infrequent and the small cost of backup heat outweighs the inconvenience of dealing with much greater storage.

I can see that with a 60kw boiler more storage might be useful as a convenience -- so again, "what do you want your storage to do that the 1250 will not do?"

Why do you feel you should have gone with more storage? Will the 1250 soak up all the heat from a single load of wood without cycling the fire?

heaterman said:

Why do you feel you should have gone with more storage? Will the 1250 soak up all the heat from a single load of wood without cycling the fire?

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I know my 660 gallons will soak up a load of wood from my boiler - but I still would like to have more storage. I think it comes down to personal preferences & schedules on this one. If I had 1000 or so, I could skip more days burning over the course of a year. For me that sounds better than just having to put an extra load of wood in when I am burning. And storage would then likely get me through being away for the weekend too - if that ever comes to happen. I just haven't figured out how to add more storage to my situation & space yet.

Ideally you should be storing solar thermal in the summer and heat through the winter with that. Probably 150,000 gallons would be more than enough.

heaterman said:

Why do you feel you should have gone with more storage? Will the 1250 soak up all the heat from a single load of wood without cycling the fire?

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It would be interesting to connect a BTU meter to large storage and see what % of the energy you put into the tank is recoverable. Unless there is 12" of insulation around a tank in a cold location, I suspect a large % escapes

Thermal storage has always been the holy grail of solar, hydronic and RE systems. You can never get back out what you put in, and how much to spend, to keep as much as possible as long as possible.

it really does come down to owner expectation, but I think the numbers would tell an interesting story. I've asked Siggy about FEA analysis of an insulated tank. Sounds like a tough problem to model with varying temperature levels, surrounding air temperature, drafts, and any flow in the tank changes the model. the BTU meter would give an accurate prediction.

Store the energy in the un-burned log, that is the best way to keep it as long as possible.

I guess the question others asked is this:

How long can you go NOW between firings.

How long do you THINK you'll go between firings with 3250?

Plan a little loss, but the math should work. You know what your high temp your boiler can run. You know your low temp that your house needs. You've got just a bit of simple 'figuring' to do.

JP

NP ALASKA said:

Thanks guys For all the insight

What i know

1250 gallons most days of the winter charge system after work and also load one load in the morning to top things before i leave for work

I would like to not have to do the morning fire

System is entirely in heated space and any loss is a benefit

I only ask becuase i dont want to sell the 2-500's i currently use if they will benefit me

I think 2250 is what i have in mind
But wanted to explore the idea a bit

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Here is a link to the journal dealing with wood fired concepts. Pages 34-37 talk about the formula for sizing buffer tanks.

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_10.pdf

And a screen shot of the formula.

There are also buffer tank simulation programs available, some online. This allows you to toggle loads and change operating conditions and get results with one click.

This is a module from HDS program at www.hydronicpros.com. May be a free demo there?

So, short answer is how many times can you be around for reloads.

I think a lot has to do with the load being drawn from the buffer. Mild day, low load is what I tried showed above with a 10,000 btu/hr load on a 1250 gallon tank 180- 140F operating range..

On a design day the boiler may run full speed, about 165,000 btu/hr output at 80% efficiency, just to cover the loads and not add any to the buffer.

I'd like to have 12,000 gallons or so (1600 cubic feet, or a bit less than a 12 foot cube.) Ain't nothing says you have to wait until it's cold to fire again - you can just fire when convenient and as much as needed to keep up, but with far less "urgency." Main thing is to have emitters that will make use of it at low temperature so you can actually swing it (ie, if you can only get it up to 180 without doing damage to the insulation/piping, and you need 150 at a minimum, you have less than half the storage you do if you can make effective use of 110 degree water and still heat the house), and insulate the bejeepers out of it so it works. In significant parts of the season that much storage would allow solar thermal to help big-time (no cutting, no drying, no hauling, no stacking), and it would allow (for me) a week or so if fully charged when push came to shove, if my heat loss is correct.

Don't know that I'll get it, but that's what I'd like. So as far as I'm concerned, there is not really a size that's too much, if you can afford it and find a place to put it. There will be a point where it does not make economic sense to go larger, but you seem to have dealt with that by getting a slamming deal.

12,000 gal, now your into a substantial standby loss

12,000 gallons..wow
so with low emitters ok...but how do you make DHW with literally tons of luke warm water...
I don't know about others, but I prefer to raise my DHW to 140f, so make is 150f-160f and at that temp sure the circs run a while, before it satisfies 140f.

So my routine is taking the DHW make up in to consideration..especially with heavy kids' laundry and endless showers.
Timing of the evening burn, I get the hot DHW demand out in the early evening during the burn and then let the storage run the radiant heat overnight down to 100f.

Do not know if I could pull that off with 2,500 gallons of storage...and batch burns..
With that in mind, anything over 1,000gallons with my system and lifestyle, would force me to batch burn..and I do not hang around for that...

But maybe there is a better way...always open...blow out the sidewall in the basement and expand the boiler room to add a used fire-tank I can get from a job I am doing in NYC-
10,000 gallons(free if I can move it out).....
hahahaha wife will have my n$*s in a vice..then a sling...shot into the stratosphere..

Scott

You could use one of the 500s as an expansion tank. Might be an appropriate size for nearly 3000 gallons.

And why do so many people think you have to run a storage tank down to room temperature before firing again? Do you always wait for the engine to start sputtering on your vehicle before stopping for gas?

DaveBP said:

And why do so many people think you have to run a storage tank down to room temperature before firing again? Do you always wait for the engine to start sputtering on your vehicle before stopping for gas?

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room temperature?

If you are referring to my post:
In my system, I effectively utilize stored water down to 100f, since my design temps for the radiant loops is 95-115 pending on outside temps..
(@10F outside to- design 118setpoint)
Thus I fire at lowest 100f(or higher pending on timing, weather etc.)....and my tanks are wrappped with 12" thick R-28 and the adjacent boiler walls are lined with 2" thick board reflective insulation...minimal loses.

I maximize my time, heat and fuel, based on system design and weather patterns.

If you are referring to something else...I missed it.

I do not see the analogy of a car engine sputtering and re firing based on stored usable energy values. Enlighten me please.

SK

Scott, I have heard people in your situation, only needing higher temps for dwh to incorporate a elec hwh. Pre heating the dwh in the indirect to what ever the radiant zone needs, then through a elec hwh to bring it to the 140 range you are looking for. The elec use age is minimal with a 30 deg delta, also allowing you to lengthen time between burns

TCaldwell said:

Scott, I have heard people in your situation, only needing higher temps for dwh to incorporate a elec hwh. Pre heating the dwh in the indirect to what ever the radiant zone needs, then through a elec hwh to bring it to the 140 range you are looking for. The elec use age is minimal with a 30 deg delta, also allowing you to lengthen time between burns

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Absolutely and thank you Tom,
we actually almost incorporated this set up, but I decided to wait my indirect out
and it has currently & surprisingly outlived my expectations.
I thought it will give up the ghost by 2012(about 10-11 years, which is what we have been seeing with them around here, as soon as 7 years dead...), but it is still going...
After it goes I most likely will incorporate a solar and electric tandem system and possibly a heat pump(nyle type) for summer usage.

In all truth, I enjoy the burning process and coordinating the DHW usage has become almost like a mental calisthenic..see how close I can dial up supply to the ever increasing hot water demand of my family..and still dump the rest for overnight heat. Getting pretty good at it..

Thank you again Tom, for the input..and
HAPPY NEW YEAR..ALL THE BEST IN 2015

Scott

I wish i had your problem, the fin tube baseboard in my house calls it quits at 135degf, not far off indirect dwh zone temp.
tom

On the dhw thing, I find if I charge our 80 gallon dhw tank up to 150 or so, it will go 2-3 days before it needs more heat. Which fits fine with a heating season batch burning schedule. Also, if you use a Johnson a419 to control the dhw heating circuit, you can utilize the dual setpoint function of it together with a thermal switch mounted on storage return to boiler pipe to do it automatically.

maple1 said:

On the dhw thing, I find if I charge our 80 gallon dhw tank up to 150 or so, it will go 2-3 days before it needs more heat. Which fits fine with a heating season batch burning schedule. Also, if you use a Johnson a419 to control the dhw heating circuit, you can utilize the dual setpoint function of it together with a thermal switch mounted on storage return to boiler pipe to do it automatically.

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I have 53gallons..and with my family..it does not last 1/2 a day..regarding the switching, I use a similar type of control to auto switch DHW make from storage to back up, when storage temps drop below 140.

Could you dedicate one of the tanks, say the 250 or 500, solely to meet DHW demands? With that tank you'd only be drawing from it to meet DHW needs so it won't contribute to the distribution heating needs. That allows you to draw down the temp on your other tanks to as low as your distribution can function at. This way you're effectively getting more energy out of the existing tanks. But if given the option for more tanks, why not?

Go as far as you can until you feel the vice clamping down...

skfire said:

I have 53gallons..and with my family..it does not last 1/2 a day..regarding the switching, I use a similar type of control to auto switch DHW make from storage to back up, when storage temps drop below 140.

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Holy crap - that seems like a lot. Although I kind of keep forgetting about the two rolls of pex I have stuffed inside my storage enclosure for DHW preheating - which in actuality likely supplies 3/4 of my DHW on its own in intermittent useage.

maple1 said:

Holy crap - that seems like a lot. Although I kind of keep forgetting about the two rolls of pex I have stuffed inside my storage enclosure for DHW preheating - which in actuality likley supplies 3/4 of my DHW on its own in intermittent useage.

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kids and a wife, that LOVE long hot showers and baths...and of course...clean up after livestock tending and triple laundry loads is a daily double routine...
when the ST-200 c$@*s out, I may go with a nyle and solar preheat in the summer and top of with the indirect feed in the winter..don't mind the timed burns