hot water tanks in series

[DaveH9]

Just starting out on a woodboiler quest, here is what we have:
1200 sf required 3 cords in an insert and 275 gals oil last year
3 lenox solar panels with a 60 gal superstore single coil
OB Weil Mcclain wgo3 with a dhw coil, 4 zones of base board, with outdoor reset
in winter the solar preheats the dhw going into the coil of the ob
in summer the ob is off and the solar supplies us most of the time
I installed the oil and solar systems

I am considering around 60k btu gasification wood boiler
I can get 4, 80 gal hot water heaters that I hope would be enough storage to run the wb efficiently.
has anybody gone that route? Maye string 2 tanks in series, 2 strings in parallel?

Thanks in advance

 

[emesine]

Just starting out on a woodboiler quest, here is what we have:
1200 sf required 3 cords in an insert and 275 gals oil last year
3 lenox solar panels with a 60 gal superstore single coil
OB Weil Mcclain wgo3 with a dhw coil, 4 zones of base board, with outdoor reset
in winter the solar preheats the dhw going into the coil of the ob
in summer the ob is off and the solar supplies us most of the time
I installed the oil and solar systems

I am considering around 60k btu gasification wood boiler
I can get 4, 80 gal hot water heaters that I hope would be enough storage to run the wb efficiently.
has anybody gone that route? Maye string 2 tanks in series, 2 strings in parallel?

Thanks in advance

I'm a novice here but....

3 cords at 24M btu per cord, assuming 50% efficiency= 36 mbtu

275 gal fuel oil at 140k btu per gallon at 90% = 34 mbtu

Your total yearly energy is 70 million BTU for heating alone.

What temperature do you need for your baseboards? For in-floor you can get away with 120F, but I suspect you will need a higher temp for baseboards. Assuming you need 150F....

320 gal at 8 lbs per gallon at 1 btu/F/pound, from 200- 150= 128,000 btu of thermal storage.

Adding to your above thermal needs your hot water, I think your storage is going to be too small.

You want storage to "layer," from what I understand. Basically you want the hot water to go in the top, and to pull the cold water from the bottom to recirculate to your boiler. When you take the water out to heat your house, you want the opposite- you want to take the hot water from the top and put the cool return in the bottom of the tanks.

Andrew

 

[emesine]

You can look at sizing from one of two ways-

I want enough heat in storage to run my house for 24 hours on most days. That way I only have to burn once per day. I am also oversizing my boiler so it will store that heat between when I get home from work and when I got to bed.

Another way to look at it is to calculate how much wood you have in your firebox, and to make sure you have enough storage to hold that much heat energy, minus what you would be using in your house at the time. A pound of wood holds about 6000 btu.

Hope this helps.

Andrew

 

[Nofossil]

Expanding on the previous analysis:

70,000,000 BTU over a heating season is around 400,000 - 500,000 BTU/day, or about 20,000 BTU/hr. Assume that your peak is about twice that. Size your storage accordingly.

In general, assume that you''l need a lot more storage than you think.

 

[jebatty]

With multiple tanks, assuming a horizontal rather than vertical arrangement, you most likely will want to plumb in parallel (feed boiler hot in top, boiler return from bottom; for heating draw from top, return to bottom) with balancing valves so that each tank will heat load/discharge at same rate. This will give you highest temp heat available from each tank.

If your system is drawing heat at the same time the boiler is firing, then plumbing/control so that boiler output would be diverted to system needs with excess, if any, to storage.

I think your ideal minimum storage capacity should be sufficient, based on normal storage starting water temp, to absorb 100% of your boiler output during a firing so as to prevent any boiler idling. This will give you maximum boiler burn efficiency. Your ideal "working" storage capacity should be the minimum plus an amount sufficient to provide required heating needs between your normal firing periods. If you have a backup heating system (such as your OB), then you may choose to have a lower "working" storage capacity and rely on the OB to meet a portion of the heat demand when storage heat has been depleted.

 

[stee6043]

For me the plumbing/connections on my tanks were a fair expense especially if you plan to plumb in some bypasses and the like. In addition to what has been said above (you should plan on needing more storage) keep in mind that there is a definite cost advantage to bigger tanks, less tanks.

Also - since everyone else missed it let me say WELCOME to the boiler room. About this time last year is when I started my EKO 40 adventure and logged on to hearth.com for the first time. I'd do it all over again in a second. You'll love owning a gasser. And you won't find a better resource than the folks on this site...

 

[DaveH9]

Thanks everyone, I will digest all this and continue. Looks like a large tank would be best and that would work better with my plans to add more solar in the future.

Dave