How much storage is too much?

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Frozen Canuck

Minister of Fire
General question for everyone to have a go at. What I am giving serious thought to is buying a used vessel (size measured in barrels not gallons) so yes very big. I intend to insulate very well with foam if I can't buy one already insulated. They are available used from a wide variety of industries breweries, wineries, nat gas, oil etc....some rated to insane pressures at temps exceeding 400 °F, some pre insulated with high temp foam, others at atmospheric pressures with no insulation....anyhow I guess my question is how much is too much??? Space is not a consideration. I will avoid the 50,000 barrel units as the freight would probably be insane. Are there any issues on size of storage Re: thermodynamics (for all you math majors) or other issues that I should consider???? As always your thoughts & input are more than welcome (helps me learn).
 
Forgive me if you've detailed your situation elsewhere but I can't remember if you have. What kind of heating loads are you planning for? Does your day job keep you away from home for days at a time?

Extraordinarily large tanks have corresponding large heat losses. Even with lots of foam insulation if it's outdoors or in an uninsulated building it still adds up to heat loss. If that heat loss adds up to a real fraction of the loads you will use then the efficiency of having all that storage is questionable.
 
Nope, Dave have not detailed the situation before. We have 2468 sq ft of living space well insulated, triple pane windows, insulated storm doors etc. So a fairly tight well insulated home considering that it is 55 years old (no foam back then). We plan to add to the heat load with an outside building for livestock & machinery & this is where most of the future heating season load will come from, hence the question as I don't want to be a slave to firing x times per day at -40 just to stay warm. Storage & boiler would be in the outbuilding & any heatloss would assist (I hope) in keeping that building warm vs just wasted btu's. Outside building is (tenatively) 28'x78' with 12' ceilings, 3 (at least) overhead doors 10'x10' each, 3 man doors. Shop area 28'x28' will need temp of say 55 when outside is -40. Livestock area28'x20' will need a temp of 40 when outside is -40 & then only when we have stock in it for whatever reason. Balance of building 28'x30' will be for boiler, storage, piping etc in one room, say 28'x12' the other 28'x18' will be for wood storage, so no heat for that area. I realize that I will have a huge area to lose heat through (entire surface of the tank) but I have also planned on 8" of sprayed on high temp foam (this is common in certain types of vessels) esp. if they have +400°F fluid in them around here. Was wondering what may be the area of diminishing returns as far as size goes. I am self employed so the more "firing" convenience the system gives me the better. Hope this helps.
 
Go for it and let us know how it works.

You'll have to run the numbers yourself as to how much heat you'll lose (more than you want in that space) vs how often you want to fire and how much more wood you want to cut.

There was a link to an article about a swedish guy with about a 10,000 gal tank, which I would guess would be about as far into the diminishing returns as I'd want to go. Look at the wikipedia article on seasonal heat storage. They mention solar heated (summertime) tanks of much bigger sizes than you're talking about, but that is to store cheaper heat for several months.

If all of us could get cheap pre-insulated pressureised tanks of that size then life would be a whole lot easier.
 
Frozen Canuck said:
Nope, Dave have not detailed the situation before. We have 2468 sq ft of living space well insulated, triple pane windows, insulated storm doors etc. So a fairly tight well insulated home considering that it is 55 years old (no foam back then). We plan to add to the heat load with an outside building for livestock & machinery & this is where most of the future heating season load will come from, hence the question as I don't want to be a slave to firing x times per day at -40 just to stay warm. Storage & boiler would be in the outbuilding & any heatloss would assist (I hope) in keeping that building warm vs just wasted btu's. Outside building is (tenatively) 28'x78' with 12' ceilings, 3 (at least) overhead doors 10'x10' each, 3 man doors. Shop area 28'x28' will need temp of say 55 when outside is -40. Livestock area28'x20' will need a temp of 40 when outside is -40 & then only when we have stock in it for whatever reason. Balance of building 28'x30' will be for boiler, storage, piping etc in one room, say 28'x12' the other 28'x18' will be for wood storage, so no heat for that area. I realize that I will have a huge area to lose heat through (entire surface of the tank) but I have also planned on 8" of sprayed on high temp foam (this is common in certain types of vessels) esp. if they have +400°F fluid in them around here. Was wondering what may be the area of diminishing returns as far as size goes. I am self employed so the more "firing" convenience the system gives me the better. Hope this helps.

If you are going to be heating a good sized home PLUS a 28' X 50' (outbuilding minus boiler room) you are going to need a LOT of BTU's my freind. Depending on the output of your boiler, you may not need any storage at all. If your outbuilding is metal, with probably minimal insualtion, 3 big overhead doors and 3 service doors, it is going to be extremely hard to heat when its really cold outside. Those overhead doors are real killers as even the best are very drafty. I would venture a guess that when its below 0 farenheit outside your boiler could be going full bore just to keep up with the heat demand of your house and the outbuilding. I'm sure others will chime in, but thats a lot to heat. Even with 1000 gallon storage tank, when it gets cold out, that tank will get depleted pretty fast.
 
Yes, easier is part of my thought process for sure, burn lots, just not as often. I can usually manage 1 day off per week & was hoping to put it to good use firing the boiler while I work in the yard. Simple math on that is that I need to store 7 mil btu's between firings, that is with no heatloss from the system at all. This should increase my eff. as the boiler will only be cold at the start of first fire after that all components at temp for the rest of the burns, never having to burn then smolder is a plus too. Was just wondering where the tipping area/zone might be, as to how much is too much, maybe a general rule of thumb or two. I will try to find some heatloss calcs for vessels of this size. If anyone is aware of any formula's that may help I would appreciate that. Thanks.
 
Sorry for the error above, the 7 mil btu's is just house load at -40. 1 mil btu's/day, I have to add load for as yet to be built out building. Hoping that won't double it.
 
Expansion tank sizing would probably be the next concern after standby losses. Not an impossible obstacle, just something to consider. While the cost of the storage might be free, cost of the required expansion tank will most likely not be free. Just food for thought. That being said, I would love to have access to a huge vessel such as what you're describing.
 
The biggest problem to a HUGE amount of storage is charging it. It's going to take a big boiler. If you deplete it in the dead of winter and then try and maintain your heat loss and charge it it will take a while. But with your idea of putting it in your out building so heat loss is there so it isn't lost I think it is very doable. I think you mentioned in another thread that those huge tanks are CHEAP there and that makes it attractive. The ex. tank isn't a problem cause you can buy another tank and use it as an ex. tank. You don't need a bladder tank. Several of us are just using propane tanks successfully for ex. tanks.
I think the dividing factor is cost of tank and cost of housing the size. Space does cost but with a tank that is already insul;ated you have make insulation a non factor.
leaddog
 
I will try to find some heatloss calcs for vessels of this size. If anyone is aware of any formula’s that may help I would appreciate that.

A good estimate can be had by multiplying the total outside surface area of the tank (in square feet) times the difference in temperature (degrees F average) between the water inside and the air surrounding the tank. That will give you the heat loss in BTUs/hour for the uninsulated tank. Divide that by the average R value of the insulation and then you'll have an approximation of what kind of heat loss you'll be looking at.

A standard comment on the forum in response to giant storage tank proposals is that it will take forever to charge back up once it is depleted.
But I don't think that is the way to run them. Keep them topped up daily (or whatever interval is convenient to your life) and burn whatever wood it takes to keep up with your day-to-day heat requirements. If the daily heat load only uses 25% of the usable heat in the tank that means if occasionally your real life (all that stuff other than your wood boiler system) requires you to be away for a few days you may be able to take off without worry because the tank can supply your needs for several days. THEN when you get back you'll have to tuck it to 'er for a number of full loads to charge it back up but you're home by then.

One question I would have about those big process tanks, though. They may be cheap to you but somebody paid a lot of money for them. Why are they so willing to part with them now for little money and not sell them to another industrial user who might pay a fair price? Are they pressure tested?

Expansion tanks are the next issue with a big tank. If you are going to use it closed and pressurized then you'll need to find an expansion tank with a useful (acceptance) volume of about 4% of the volume of the storage tank plus the rest of the system.The acceptance volume will be 50% or less of the actual expansion tank size. You could make one from a propane tank or other vessel capable of taking the same pressure that the rest of the system will hold and just monitor the air volume in it or keep your eye out on Ebuy (or perhaps the same guys selling these process tanks you're looking at) for a big industrial expansion tank. I've seen them occasionally. Even used they're not cheap.

I don't mean to discourage you. Not at all. Just want to make sure you're shaking ALL the dice before you throw them.

Remember the great philosopher, Mae West, said too much of a good think can be wonderful.
 
DaveBP: Thanks for the formula on estimating the heatloss for tanks. I agree that not depleting the tank would be the better way to go, a fire before I leave & when I return works for me, top up on day off. Even then I only need to do that at my design temp of -40. As to the process tank question; essentially they are all not needed anymore by their owners, as virtually all companies are trying to get bigger to lower there cost per unit produced, so they sell their 600 barrel vessel & buy a 6000 barrel vessel & so on until they are selling a 60,000 barrel vessel & buying god knows what to increase production capacity, some are rentals & have been returned, as to price I feel the biggest factor is the downturn in the economy, more vessels in storage yards than there are buyers for them, & with investment capital being tight they need to sell them to generate cash as opposed to the expense of storing them. Try a www. search for "used storage tanks/vessels" & see what is available in your area, I have found several companies south of 49 selling vessels but the freight from there to here makes it a no go. As to pressure rated, yes many are; some to insane pressures +600 psi at +400 °F. Plenty with multiple fittings on tanks, some with just a couple. No way I will get close to that temp or pressure on the farm heating water (probably against the law for me to try) ;-) I am not sure if I will go pressurized or just atmospheric, if I choose not to pressurize then that will limit my tank options as I will need the top of tank to be the same height as top of boiler unless I valve it to prevent overflow. I have seen a system like this, boiler was made by Herlt (german I think) I have asked & they wont/can't sell me a boiler here, the videos were by a consulting company over there, they are posted on Youtube, but they did not go into the nuts & bolts of the system & my German is not what it should be. I agree with you about having a good plan before executing it, as I don't want to be in the situation of having a large vessel that I have to bypass because I did not plan/think it through. That for me would be the worst outcome.
 
From my math, 7-10 million btu/day (depending on insulation) should take care of you. Lets go on the big side and say 10 million btu/day. You need 6 days of storage (firing on the 7th day). So you need 60 million btu of storage. Assuming a 50 degree swing is possible (running your tank from 200-150F for instance), that would mean you would need 144,000 gallons of storage (4,645 barrels).

No you need to charge that beast. Lets say you take 24 hours of burn time to charge that tank, you would need a boiler putting out a steady 2,500,000 btu. Even if you did only need 7 million btu/day, that would still leave you needing a boiler capable of a steady 1,750,000 btu. I don't see that happening unless you build your own beasty boiler.

Please, someone correct me if I'm wrong.
 
Thanks for the math Joe; my usage now is 1mil btu/day so that would be 7mil btu/week house only at design temp of -40. So I would need 7-10mil btu of storage for a week of -40. The outbuilding should consume less btu's than the house as the temp will be no more than 55 °F in the outbuilding. I plan to insulate well R40 walls R80 ceilings foam under all the concrete & perimeter etc. I realize that the biggest factor will be keeping the doors closed as much as possible esp. when it is that cold. So if I can cover all loads with 10-15 mil btu/week I think I can find storage for that I will check back on different delta T's to determine the volume of water needed & then calc what boiler fire rate I might need. Thanks for the help.
 
Ah, my house's design load is -10F and 1 million btu/day. My house is only 1250 sq feet. So I figured double the house and -40F and you would need way more than me. BUT my house isn't anywhere near as insulated as yours.

Even at 1.5 million btu/day that is still 9 million btu per 6 days required. So with the same 50 degree delta T of the tank, that would mean 21,600 gallons (~700 barrels). And with a 24hr burn you would still need a 375,000btu boiler. This however is possible because I have seen 500,000 btu owb units. At 500,000 btu, you could charge your 700 barrel tank in 18 hours.

So I guess it is possible, but still a huge amount of storage.

My little house would require a bit over 10,000 gallons to supply my heat for the coldest week of the year.
 
Thanks Joe; hoping to achieve a higher delta T. 80 should work as my fan coils in the house are 2x the design size & keep the house warm at 110-120 water temp. DHW is an indirect water heater & does well at extracting the btu's avail to it. I plan to use tubes in outbuilding floor for majority of heat + maybe add a fan coil for the shop area for fast warm ups.
 
Keep in mind that average winter daily heat load is typically half of 'worst day' load, and if you have any solar gain (south-facing windows) it can be much less if the sun is out.

Second issue: One of the biggest potential problems with having a huge storage tank is that if you can't maintain excellent stratification the tank can be an impediment to heating. 10,000 gallons at 130 °F is nowhere NEAR as useful as a 10,000 gallon tank with a thousand gallons at the top at 180 °F and the rest at 125 °F.

If you're not pressurized and have a heat exchanger between the tank and the boiler, the HX will make it difficult to get high storage temps.

I'd be very hesitant to run unpressurized without a HX since you'll get a lot more corrosion of the wood boiler and other ferrous components.

To maintain stratification you also need as low a return temp as possible when heating from the tank.
 
Frozen Canuck said:
...
used vessel
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very big
...
other issues that I should consider?

A very big vessel will tend to have thick steel walls, which would be better than thin walls for conducting heat from top to bottom, which would degrade stratification.

You could end up maintaining a thick layer of water that has limited usefulness for heating, but is hot enough to lose heat to the environment through the insulation at all times nonetheless. Standing the tank on end would help a lot.

--ewd
 
NoFossil; thanks for the reminders, easy to get tunnel vision & forget the important details. I agree we see a lot less -40 here in the winter than say 20-30 years ago, yes we have lots of solar gain we oriented the house & built it with this in mind for example the SW facing wall is 44'x8'=352sq ft. It has 131sq ft of glass in it, so 37% glass, all windows are bays to let in more light + a dbl garden door out to the deck & when the sun is out lots of solar gain. We like that all winter but it can be tricky juggling awnings up or down in the summer.

I agree on the need to have good/excellent stratification otherwise the extra storage is wasted for the most part. I have been tossing around various ideas such as smaller pumps, delta T pumps, a smaller storage vessel in the house (200 gallons approx) that is filled/depleted/then refilled & any other practical ways of assisting stratification, as well as reading how others have dealt with this in their posts. Plenty of ideas here question of which one suits our situation best.

I have not decided yet as to pressurized or not, was not considering a HX between boiler & storage for the reason you state. Thanks for the confirmation.

I was actually considering running unpressurized without a HX (between boiler & storage) & yes I would need to buy more treatment chemical as well as sample water in the system on a regular schedule, so I am aware of PH levels & water quality/clarity. The only ferrous compionents would be in the outbuilding; iron pipe from boiler to storage, short run of iron pipe out of storage, then Pex Al Pex, HX & brass pumps from there on. At least that's the thought.

Agree on needing to maintain as low a water return temp as possible just a question of how best to do that.

Thanks for all the input more food for thought.
 
A thought on running an unpressurized steel tank. My experience is that even with corrosion treatment in the tank water, the
interface between the tank water and air will tend to corrode. Anyone else seen this?
The boiler will be protected by the treatment.
 
ewdudley; Yes I have noticed that some of these vessels have 9/16" walls or thicker esp. those high pressure high temp ones. Thanks for the reminder on conduction losses with those thick walls.

I agree my thought was to stand the tank on end to get better stratification, this would also give me more options in the area of the tank that I am sending hot water to/drawing cold water from, as many of these tanks have multiple fittings as well as a manway access for inspection/cleaning. So I am trying to limit my searches to vessels that are no more than 8' in diameter (have to haul it down the road legally) & not disconnect/reconnect all the power lines between here & there. No special permits etc. otherwise cost becomes prohibitive.

If I remember Hanson posted something similiar to what I am considering, I will try to find that post & see what I can learn. BTW the EU sites have lots of info on storage some of it huge, translation can be a bit of a problem (for me) though.
 
Tom; Thanks for the info on possible corrosion in the tank. If that is the case I may have to restrict my searches to SS vessels to avoid the possible corrosion you speak of. Just athought as I am by no means an expert in this area, however if this were true wouldn't the Garns be affected by this as they are unpressurized???? Dunno.....more food for thought for me.
 
I think Tom is right that where the air is allowed to come in contact with the steel will be a likely place for corrosion, despite treatment chemicals. No experience here, just seems very probable.
I remember Hansson's upstairs open expansion tank being stainless steel and I think I have seen stainless noted elsewhere and this may be why. I'm going to use an open expansion tank on my system and I acquired a 60 gallon 304 stainless steel tank from a neglected Ebuy auction for less than the price of the stainless in it. That will be the only place air touches the walls of the system and near the bottom of that stainless tank is where I'll put the low water cutoff attached to the alarm so no air will get down any lower in the system.
If you could get a tall narrow stainless tank at least 5% of the total volume of the entire system and mount it at the high point of the unpressurized portion of the system and let all the expansion (the 'tidal' action of water in and out as the water expands and contracts with temp change) happen in there that might eliminate actual air contact with wet steel.
I only suggest tall and narrow vertically mounted to as to present the smallest surface area in contact with the air. I don't know if it makes any real world difference or not.

I think the easiest way to optimize stratification is if you have your connections somewhere near to the top and bottom and use the largest pipe you can for the last several feet so it slows down the flow of water as it enters the tank.Tanks that big would have pretty big ports in them ready to use, I would think. With any luck they would have valves on them, too.
 
Ok, fair enough so a stainless steel expansion tank at a minimum it is, thanks for the input it really helps in the process, better to be aware of possible problems & plan/prepare for them prior to construction.
 
Don't give up on using pressurized . It has several advantages and if the tanks are pressure tanks I'd never even think about nonpressurized. You are only talking 30#.
leaddog
 
leaddog; ok, if I go the pressurized route does that limit my boiler choices to only those designed to operate under pressure? Could I install some sort of motorized valve between boiler & storage that would allow any boiler to operate in the system??

Just a side note for you (math majors) how much force is involved in a vessel 10,000 gal - 15,000 gal at 30 psi? Hopefully not as much as my paranoid mind just imagined!!!! :bug: :bug: :bug:
 
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