How much storage is too much?

[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:

I didn't think about you using anything other than a pressure boiler. The only nonpressure gasification boiler I know of is the garn and I wouldn't think of going with anything that wasn't gasification because of the amount of wood you are talking. If you go with a non pressure boiler then going nonpressure would be ok. No sence using a heat ex if you don't have to. But remember that chemicals are very expensive for the large gals you are talking.
I don't see where you would have any problem with pressure as the only place you would build high pressure would be in a overheat situation and I can't forsee you overheating 10000gals.
leaddog

 

[Frozen Canuck]

leaddog; If I were to go the Garn route would I need some kind of valve between that & storage to prevent the storage from forcing water out of the Garn overflow tube? There must be something on the market that would allow this to work I assume because the storage in a large commercial setup for example would need to be much larger than what I am thinking of just to allow for maintenance/service/repair/replacement of the boiler while still allowing the building to be heated during an extended down period for the boiler. At least I hope that is the case, you been there done that types are better suited to answer that though.

 

[thecontrolguy]

Heya Canuck;

Hope this wasn't mentioned yet .. why not consider the large pressurized tank, at 30 lbs max, and leave an air cushion in the top of the (vertical) tank that would function as the expansion space. So, a very large expansion tank that just happens to be the heat storage tank as well. You could even fabricate a level column to view thre level of water and the amount of air present. This is a normal part of many commercial boiler systems and is available many places. Thoughts from the gang?

 

[ewdudley]

Heya Canuck;

Hope this wasn't mentioned yet .. why not consider the large pressurized tank, at 30 lbs max, and leave an air cushion in the top of the (vertical) tank that would function as the expansion space. So, a very large expansion tank that just happens to be the heat storage tank as well. You could even fabricate a level column to view thre level of water and the amount of air present. This is a normal part of many commercial boiler systems and is available many places. Thoughts from the gang?

There you go, a sight tube. As long as the lowest level is high enough, it's good enough. I can't see any disadvantage since you'd need to keep an eye on the water level in a separate expansion vessel anyways. I wish I'd though about this more seriously when I set up my tanks.

 

[Frozen Canuck]

Control: sounds like a good idea a sight glass/tube on the expansion tank, should let me know from the ground if I need to add water to the system. Beats climbing a ladder. Still have the same question as to whether or not it is possible to add this size of storage to an open system boiler like a Garn. Anyone care to take a swing at that????

 

[ewdudley]

Control: sounds like a good idea a sight glass/tube on the expansion tank, should let me know from the ground if I need to add water to the system. Beats climbing a ladder. Still have the same question as to whether or not it is possible to add this size of storage to an open system boiler like a Garn. Anyone care to take a swing at that????

I believe it would be possible if you sealed the manway and extended the Garn vent with 2" diameter or so vertical vent pipe from the Garn that extended high enough to let the Garn water level to match the water level in storage. But I doubt Garn would sign off on it

In this case if the storage doubled as the expansion vessel then the top of the storage tank would need to be vented, which would allow fresh oxygen to breath directly into storage water, a real NOGO in my opinion. I you had a separate expansion vessel at a level higher than any other component in the global system (known in the Boiler Room as a European expansion cistern) then expansion breathing would affect expansion water which hopefully wouldn't be as big a problem. It's also been noted that 'parafin oil' can be floated on the surface of the expansion vessel water to prevent breathing.

Since the advantage of the Garn is integrated storage and supposed efficiency, and since you're proposing a storage volume that may be higher than optimum to begin with, then using a Garn can only be justified if its actual efficiency outweighs the expense of adding storage you don't need. So get a Wood Gun.

 

[DaveBP]

One of the reasons a Garn costs so much more than a good gassifier boiler alone is that it has storage built in to it. And that is some pretty premium priced storage on a gallons per dollar basis. If you can get good usable storage at a good price and you need more than the largest Garn provides why pay so much for not enough? And limit yourself to unpressurized installation?

To get an idea of the forces involved in a pressure vessel you multiply the surface area by the unit pressure.

For those of us south of the border an example: My 500 gallon propane tanks have a surface area of a little over 100 square feet (says so on the label plate). A hundred square feet is 14400 square inches. Multiply that by the typical 30psi pressure relief valve setting and you a closing in on half a million pounds of stretching force trying to make that tank another size larger. 30psi is the high limit but for folks trying to save money by buying the least expansion tank required (they are expensive) the pressures at max temperature will get close to that on a day-to-day basis.

Most propane tanks I've seen are rated at about 250psi @300F (or so) temperatures. I would not buy any tank that didn't have an original manufacturer's pressure/temperature rating plate welded to it somewhere.

(Except a propane tank, maybe. They often have their plates removed when they are retired but they are all vastly overbuilt for the typical boiling water/30psi max pressure that is used in most residential or small commercial setups).

 

[Frozen Canuck]

DaveBP:

Fair comment re: the Garn.

The reason it is at the top of my list is twofold;

(1) After much reading here & elsewhere they seem to be the most reliable of the North American units, fewest problems reported, long service life when maintained, proven track record over an extended period of time, simple operation (important if I am away for extended periods & someone else fires the boiler), no need for complicated controls or boiler protection also important when I am away...btw I expect to be away more often & for longer periods with the current economy.

(2) They were the only one to respond to my emails & give me a price for the unit I was interested in (I know go figure in this economy). So in a nutshell I am looking for ways to make this unit serve the needs of the house for longer periods when I am away, don't get me wrong if the Garn is a no go with extra storage then that is just a simple fact, can't change reality. Hope this helps to explain my interest in all that storage.

 

[Como]

Buy 2 Garns.

The Garn comes with a chemical pack for the water.

Non home brewed storage is very expensive, makes the Garn look reasonable.

When you come back you will need to re heat all that storage and will need a lot of firebox, hence my comment about 2 Garns.

The more logical solution would be to store the heat in wood not water, for that you need an automated system using pellets or chips. Or use propane/gas/electricity to keep the building above freezing.

 

[Frozen Canuck]

Como: 2 Garns = 30k + install costs (approx), just not in the budget. It seems that the tipping point where cordwood stops & chips begin is about 1 mil btu/hr fire rate. Small chip system of 1 mil btu/hr makes 2 Garns look cheap by the time you add all the equipment to automate it. Just the way it is. That is the reason for my inquiry on adding larger storage. Just looking for ways to extend my time between firings. Maybe I am on a wild goose chase. Hope not.

 

[Como]

I would have said $40K would be nearer.

The problem with chips is that you need to store them somewhere they will not freeze into a solid block.

I have looked at this myself and decided the cost/benefit of storage of this size is just not there, in my case Propane makes best sense as a back up/top up. YMMV

As I need back up, Propane will be there anyway, cost of storage in Dollars and space to add additional water storage with limited use and low efficiency is just not there. And like I mentioned once it is used up you have a major issues in getting it back up again.

There are of course smaller pellet boilers, with probably a lot more options coming. Viessmann/Kob make a nice one that will do both. Cord and Pellets. Probably be in Canada before US.

 

[joecool85]

I'd seriously consider doing a Garn with a pellet boiler as backup. Then the only thing anyone would have to do is periodically clean the burn pot on the pellet unit and while you are around you can burn cord wood and save money.

Any reason you can't get a Garn and have someone load it once a day while you are gone? This would be the best and easiest solution to your problem if you want to burn wood. Otherwise, propane is looking better and better eh?

 

[leaddog]

I think the garn would work well in your situation. You would need to use a heat ex to your storage but they have a quick recovery and you could pipe it so you would pull heat off the boiler first so when the storage was down you would have heat fairly quick and then heat the storage. Having your storage inside any heat loss would be where you need it and would help when you are gone. From what I can see they are probably the easiest to lite fill and forget of any of the boilers. They also have a huge btu per hr burn, Like I think 500000btu/ hr so you would beable to repentish the storage. and In the shoulder seasons you could just run the garn and not charge the storage. If you can get those large tanks that are insulated I think it's doable. I'd run this by heaterman as he is a dealer and would be able to give you a better idea.
leaddog

 

[Como]

I'd seriously consider doing a Garn with a pellet boiler as backup. Then the only thing anyone would have to do is periodically clean the burn pot on the pellet unit and while you are around you can burn cord wood and save money.

Any reason you can't get a Garn and have someone load it once a day while you are gone? This would be the best and easiest solution to your problem if you want to burn wood. Otherwise, propane is looking better and better eh?

Whilst this is a nice concept, the problem is cost.

A Pellet set up could with silo etc cost $20,000 rather than a few thousand for a fossil fuelled burner. And as it is not being used as a primary the pay back period can be very long.