How to size a storage tank

[scottinkn]

Hello,

Is there an actual chart of reference to sizing a storage tank?

Or pretty much general rules of thumb?

I know in the dead of winter in MA I would only like to fire 1x a day (I hope)

I am installing a 130,000 BTU wood boiler and I have 1920 total sq ft. (960 on each floor)
Solar panels to soon follow.....
(not including cellar(which is not living space))

Thanks,

Tink

 

[stee6043]

You should "size" the tank based on how many btu's you want to store. For me I find useable storage temps to be between 180 and 140. So for 1,000 gallons in that temp range you'll have roughly 332,000 useable btu's. If your average daily heat load is in the ballpark of 30,000 btu/hr you'd have 11 hours of heat in this tank.

I find my average heat loads to be closer to 20,000btu (or lower with some sunshine) so I typically run close to 16 hours on storage. Although I prefer to not take my tanks all the way down to 140 whenever possible...

 

[in hot water]

www.pmmag.com/Articles/Column/ac719ac235fc7010VgnVCM100000f932a8c0____

Doesn't look like the graphics show up at this link/ for some reason

tank volume = Vb X e X d X 7000- Lbuilding- Lburn divided by 8.33 x delta t

The example in the article should work out to 220 gallons

This formula shows a 40,000 BTU/hr load while charging the tank also.

coast time = 8.33 X V X delta t divided by L

credit Appropriate Designs John Siegenthaler

4.6 hours for this example

hr

 

[joecool85]

Hello,

Is there an actual chart of reference to sizing a storage tank?

Or pretty much general rules of thumb?

I know in the dead of winter in MA I would only like to fire 1x a day (I hope)

I am installing a 130,000 BTU wood boiler and I have 1920 total sq ft. (960 on each floor)
Solar panels to soon follow.....
(not including cellar(which is not living space))

Thanks,

Tink

Using the math from stee6043, and the assumption that you would use 75,000btu/hr when it is the coldest of cold (-20 in the morning, 0 during the day) that would give you about 4.5 hours. That said, I'd imagine during the "regular" cold parts of winter (December through February), you should be using something like an average of 25,000btu/hr and that would give you about 14 hours of heat. So, to get a full days worth of heat for you, you would need 2,000 gallons of thermal storage.

If you have radiant floor heat, and you don't mind running your tanks way up and way down (you need mixing valves for radiant anyway, so it's not a big deal), you could start at 190 and run down to 110 and get away with a full day's heat on 1,000 gallons. If you have baseboard heat, you really need 2,000 gallons for a full day. The cool thing is that in the spring and summer you will get about a week per burn!

 

[scottinkn]

Well thanks for the input guys!

I do have baseboard HW heat.
So if I put the tank inside, next to boiler, tank size can only be approx. 4 x 7 so around 800 gallons....My only other option is further away under a bench or outside which size can be 4 x 12, about 1400 gallons.

See I would like to only burn for about 4hrs a day, full out, if possible. ((on average)(not including solar))

I don't want to spend half a day getting a tank up to temp.

would it be better to have a smaller volume at higher temp or larger volume at lower temp?

Is it possible to oversize a tank?

Where would the point of diminishing returns be in tank size?

Anyone experienced in this problem?

 

[joecool85]

Well thanks for the input guys!

I do have baseboard HW heat.
So if I put the tank inside, next to boiler, tank size can only be approx. 4 x 7 so around 800 gallons....My only other option is further away under a bench or outside which size can be 4 x 12, about 1400 gallons.

See I would like to only burn for about 4hrs a day, full out, if possible. ((on average)(not including solar))

I don't want to spend half a day getting a tank up to temp.

would it be better to have a smaller volume at higher temp or larger volume at lower temp?

Is it possible to oversize a tank?

Where would the point of diminishing returns be in tank size?

Anyone experienced in this problem?

Ok, one question at a time.

In your case due to the baseboard heat requiring a minimum of 140 to get any substantial heat, it is better to have a larger tank with smaller temp swing.

Effectively it is not possible to oversize a tank. It could be done, but it would have to be 4,000+ gallons.

Diminishing returns, well, it depends on the building and your boiler. For you I would say 2,000 gallons is good, anything more than that is probably a waste or at least only slightly better but with much more money and space taken up.

 

[in hot water]

I think you want at least enough storage to get through the night without refueling. It's a pain the start a new fire every morning. So the size of storage will vary depending on your load, the size of boiler and firebox, and how well you insulate everything to keep the tank hot.

The boiler needs to be large enough to handle a design load and have some power left to charge the tank at the same time.

In a perfect world the boiler would be sized to the largest load, be able to modulate, and never run out of fuel.

For that type of operation, pellet boilers seem to come very close to "ideal" almost like having a gas or oil fired boiler.

The other variables are type of wood, moisture, a clean stove, how well the fire is built in the stove, etc. It takes a few months or more to get the routine down.

It's a great feeling when it all clicks and no gas, or oil is consumed to heat your home and DHW.

For most the juice is worth the squeeze. Planning it all out on paper and via simulation software helps a lot.

hr

 

[SolarAndWood]

In a perfect world the boiler would be sized to the largest load, be able to modulate, and never run out of fuel.

How close to this could you get with a boiler like the Froling? Seems you should be able to get away with a much smaller tank if all it has to do is smooth out the bumps of a boiler that can efficiently shut itself down and restart again? Maybe even get to one load a day that fires itself a few times? In the summer, burn a partial load, just enough to charge the tank for dhw?

 

[scottinkn]

Well I just want to fire 1 X a day hopefully for no more than 4 hrs.....

 

[webbie]

this is a crude calculator, but may help a bit
https://www.hearth.com/talk/calculators/water-storages

 

[scottinkn]

That crude calculator is GREAT!

Now that is a good clean no frills example of what I was looking for!

(The answer even gives an example that is easy to understand)

Thank you very much!!

BTW I am in wmass too!