I'm missing something

[dmacfarland]

Lots of talk here about heat storage, and I was wondering you already have the energy storage, its in the wood. Why not burn it at the rate you need and forget the massive tanks?

It doesn't seem an insurmountable task to modulate a wood fire, or to turn it on and off say every hour or so with a much smaller storage tank.

 

[ihookem]

Well, that seems to be the thinking of us without storage. I still want storage though but only about 100 gal. The reason is so I can heat the house a little faster when I get home from work. I don't know if it will work and figure most will say I'm wasting time and money. With 35 gal. of water it doesn't take long to drain the heat out of it. With 135 gal. I think I can heat the house before I run out of hot water.

 

[Gooserider]

Lots of talk here about heat storage, and I was wondering you already have the energy storage, its in the wood. Why not burn it at the rate you need and forget the massive tanks?

It doesn't seem an insurmountable task to modulate a wood fire, or to turn it on and off say every hour or so with a much smaller storage tank.

The problem is that ANY fuel has a certain natural "burn rate" at which it wants to combust and put out heat most efficiently. Burning faster or slower than that ideal rate leads to inefficiency and wasted energy... With fossil fuel (other than coal), it is possible to modulate the fire by controlling the amount of fuel going into the combustion chamber and thus match the rate of heat output to the rate of demand reasonably closely, so as not to need thermal storage....

You can also modulate wood the same way in theory, as long as you have lots of small particles, like a pellet or wood chip boiler, though those have their own other issues. However when your "fuel particle" is the size of a cordwood split, modulating the fuel supply is not going to work... OTOH, modulating the air supply, which is the other option, leads to smouldering and lots of smoke and creosote production.... Turning a wood fire "on and off" is not the relatively trivial matter that turning a gas or oil burner on and off is.

IOW, we agree, the best thermal storage is in the wood, to the extent that it's possible, which is why you don't see us advocating really huge tanks for the most part, but just enough to hold 12-24 hours of peak demand, if that. The reason we push moderate amounts of storage is to serve as an "impedance match" between the way that wood wants to be burned in order to give the greatest possible cleanliness and efficiency, which is a hot, fast burning fire that puts out a lot of heat in a short period of time, and the relatively low and slow demand of the typical house load

Gooserider

 

[leaddog]

The other reason for storage is so you DON"T have to babysit the fire. If I'm gone for a day in the dead of winter I don't have to worry about coming home to a cold house. I also don't have to get up early in the morning and if I'm tired I DON"T have to go out late at nite. Makes it alot more conveniant.
The other reason is I burn year round and in the summer I build a fire once a week and heat my DHW and hot tub and waterbed and don't pay the elect co.
My son works 12hr shifts 3 on and 2off etc so he uses storage to manage his heat so he only has to fire on his days off.
leaddog

 

[Nofossil]

Goose as usual offers a perfect explanation. The only thing that I can add is some numbers. When boiler manufacturers have their units tested for efficiency, it's ALWAYS at full output. Why is that? Because that's where you get the best efficiency. You can modulate wood boilers a little bit, but if a wood boiler is just big enough for your peak demand, it's going to be running at an average of 50% load. Efficiency at 50% is MUCH lower.

I ran my first season without storage. I didn't see a big efficiency hit, but I ended up making lots of little fires and the temperature in the house fluctuated a lot. Storage allows me to run my boiler at peak efficiency all the time, on my schedule and at my convenience. The house temperature stays right where the thermostat is set. As mentioned above, I can skip days if it's not too cold. No question that storage is great if you can do it. Also no question that you can be happy and warm without storage.