what is the idea behind water storage??

[cvanhat]

just wondering because the manual for the eko 60 reccommends water storage tanks. do you put these in your cellar near the oil burner?? just wondering what the logic is, i see alot of people talking about it on here. thanks

 

[Eric Johnson]

Hot water storage is like a battery--you charge it up with heat and recover it later. This allows you to run the boiler at full capacity regardless of the weather, which is the most efficient way to do it. You can also heat the tank in the summer for your domestic hot water. It can stretch out the time between firings and help get you through those sub-zero nights without having to get out of bed in the middle of the night to toss wood into the boiler.

In short, it's a really good idea.

 

[webbie]

If you look at most well engineered systems, from computers to hydro plants (dams), the utilize "buffers" or cache to store and deliver services at various levels based on the demand and supply. So, as Eric says, this does the same with wood boilers......but the benefits in this case are more than just using the power (heat) when needed, it just do happens that a wood system burns best at one output...usually full. So you have two benefits, the heat storage and the higher efficiency.

 

[cvanhat]

so how do you figure how much storage you should have, or does it not matter too much??

 

[Eric Johnson]

The old line was that you can't have too much storage, but there are inevitable standby losses, so it pays to use some restraint. One thousand gallons seems to be what most people shoot for, but you can get by with less with a smaller boiler. It probably doesn't pay to have less than 500 in any event, though even a 40-gallon hot water heater will have a positive impact on a wood-fired boiler, in that it tends to even out the burning cycle and (in my experience) improve efficiency some.

Another point alluded to in my previous post is that you burn less wood with storage--up to 40% less by some accounts. When sizing nonpressurized storage, bear in mind that you use the same heat exchanger whether you're storing 200 gallons or 2,000. Since heat exchangers are pretty expensive, you're probably ahead to spend a little extra on more storage, rather than less, since you'll see a lot more benefit for the relatively small extra cost.

 

[Nofossil]

In answer to another of your questions, storage is ideally located near the heat loads - DHW tank, baseboards, radiant zones or whatever. Couple of things to keep in mind: You'll want to insulate the storage as well as you possibly can, and you want to promote thermal stratification with the hottest water at the top and coldest at the bottom. Pressurized storage can make this a little easier to accomplish, and saves you at least one heat exchanger.

If you have a radiant zone in your house, that allows you to use stored heat down to a lower tank temperature, increasing the effective heat storage per gallon of tank size.

 

[webbie]

The amount can be easily calculated because the definition of a BTU is the amount of heat to raise one pound of water one degree.

This also points to another potential direction for someone planning a new or updated system - one capable of getting heat from water that is colder than usual - say 120 degree water instead of 160+.

This allows more draw down of the storage - lots more BTU's in lowering 190 degree storage down to 120, then lowering it down to 160!

 

[jebatty]

Also useful, if possible, to locate storage tank in an area to be heated. Even with needed insulation, all lost heat will simply be providing needed heat. Could be a significant increase in overall efficiency. Similarly, locating boiler in the heated space, rather than in an unheated space.

 

[chase2378]

So, let me see if I understand. My OWB will make the heat, then I also need something else to store the water in? Would I store it inside my house? Say in the crawlspace where my oil tanks are?

 

[webbie]

OWB's often have quite a bit of storage built into the units themselves....and depending on the model, storage may not help very much.

Smaller indoor boilers like the EKO mentioned have rather small water capacities...and are also designed so as to run most efficiently when at full bore - hence the need for storage.

 

[chase2378]

OIC, I'm looking at a Greenwood Aspen Model. Do you know anything about it's storage capacities? Also, are there pellet boilers on the market that do the same thing a OWB does but that dont require me becoming a wood rat?? :coolsmile:

 

[Ecky]

Hot water storage is like a battery--you charge it up with heat and recover it later. This allows you to run the boiler at full capacity regardless of the weather, which is the most efficient way to do it. You can also heat the tank in the summer for your domestic hot water. It can stretch out the time between firings and help get you through those sub-zero nights without having to get out of bed in the middle of the night to toss wood into the boiler.

In short, it's a really good idea.

As indicated by Eric, hot water storage does make a lot of sense. Consider also that the water storage can be used in combination with a solar collector to provide thermal storage in the shoulder seasons and the summer and as such, you could avoid having to fire up your boiler at all during the summer! Certainly something to think about. This is where something like a GARN makes sense IMHO. Cheers.

 

[sandman59]

When using water storage, does this mean that the fire will burn full tilt heating the water in the storage, then when the wood is exhausted, it goes out? Do you have to start a fire every time after the full fire cycle? Typically, how long would the burn cycle be for an EKO 40 with a 1000 gallons of storage?

 

[Ecky]

When using water storage, does this mean that the fire will burn full tilt heating the water in the storage, then when the wood is exhausted, it goes out? Do you have to start a fire every time after the full fire cycle? Typically, how long would the burn cycle be for an EKO 40 with a 1000 gallons of storage?

You are correct in your assumption, the fire burns full tilt (and therefore at maximum efficiency) until the wood goes out at which time the fire goes out. You start a fire every time you've used up the stored BTU's. Depending upon how cool things are, and if there are any coals leftover, you may or may not have to re-start the fire. The fire starts very easy if you have dry wood. It is aided by the fan. I have no idea about the EKO but basically you take the stored BTU's (920,000 going from 200 to 120 degrees in a 1400 gallon tank) and divide that by the BTU's required per hour to determine the time needed between firings. Hope that helps!

Cheers,
Paul