First Steps in Planning Water Storage

[Bad Wolf]

Superman If you are going to have storage it's going to occupy "X" amount of space. You can use square or rectanular tanks to make better use of the space but at the end of the day 800 gallons or 1200 gallons are going to take up a certain amount of space. Mine is 7 1/2 ft accross and holds 1200 gallons. 1200 x 8.328 is about 10,000 pounds x 40 (172-142 degrees) gives me about 400,000 BTU's of storage. This is enough to keep me going from 7 in the morning to 5 in the evening when I get home on even the coldest days. This past weekend I went from Sat at 5 to Sun at 8 before I built another fire

3000 sq. ft house, & DHW I've used 4 cords but this is my first year burning.

 

[Medman]

While we are on the subject, I just searched and cannot find the calculations for storage size.
example:
Heat loss = 42000 btu/h worst case
Min temp = 140*, Max temp = 180*
min 8 hour draw from storage time
Boiler output 80,000 btu

How big should the tank be worst case?
I know there is a btu/gal/deg rise formula but can't find it.

Thanks

 

[Piker]

delta "T" x gallons x 8.3 = storage capacity in Btu's.

min 8 hour draw would require 336,000 Btu's stored.

so

(40*) x gallons x 8.3 = 336000
gallons = 1012

should be able to charge the tank and heat the house on the coldest day in a little over 8 hours.

cheers

 

[Bad Wolf]

1 btu raises 1 pound of water 1 degree F. Sooo…
42,000 x 8 hrs = 336,000 btus divide that by the 40 degrees you hope to get out of your storage gives you 8,400 lbs. Divide that by 8.328 (weight of 1 gallon water ) gives you 1008 gallons. Now that’s in a perfect world, in reality you have standby losses, transmission losses and others.

Also with a boiler output of 80,000 btu/hr times say 75% efficiency, you have 60,000 btu/hr so it would take 5.6 hours to put that many btus back into your storage, provide there were no other demands on it.

Actual mileage may vary…

 

[Medman]

Thanks for the quick replies! Those numbers are what I ended up with in the last few minutes. I am rethinking storage now - perhaps going with 1000 gal unpressurized. I'm going to look at your thread about the tank again, Greg. At $300 per 500 gal tank plus circs and pipe, I could probably build a bigger tank for less. I know I can get polyiso and EPDM locally as well. I definitely have room in the boiler room for the tank.

Any quick recommendations for a flat-plate heat exchanger for this size of heat transfer?

 

[Fred61]

Superman,

Did I read in one of your posts above that your flue pipe gets so hot that it sizzles when you spit on it? I don't want to insult your intelligence by asking this question but here goes. Are you closing the damper after loading the firebox with wood? If it is left open that would cause the pipe to be hot, fill your flue pipe with ash and produce very little heat which are all symptoms that you describe in the above posts.