OWB issues
How does the heat get thru the fire brick to get to the water jacket to heat the water? I realize the WHOLE firebox isn't lined with the brick, but covering any of it up limits the heat transfer area of the water jacket, acting like an insulator. And that in turn would naturally raise the temperatures in the firebox because it can't be transferred thru the area that the fire brick now occupies. At least that's the way it plays out in my mind.
Can boiler plate be rolled into a round shape? I always thought it was too brittle for that kind of forming.
If I had to split down my wood into something like that used in an indoor wood stove, it would kind of take away an advantage I have of not having to handle the wood more than I already do.
I used to sell and deliver coal, so I'm a little familiar with it, and yes, it provides a nice, even and HOT heat. But around here, (and probably anywhere else where it's not mined near-by), it's going for over $250 a ton. Judging by what I know about coal, I would need about 30 tons to get me thru a season, and that would cost about $7500. That's about what I spent in fuel oil this year, so where's the advantage?
Actually, there are a number of manufacturers of OWB's, both conventional and gassers, that use multiple heat transfer tubes. My friend up the street has one made by, (I think), Tarm. He is CONSTANTLY having to clean the tubes because they plug up with creosote. And he's using seasoned wood. I can't imagine using green wood. He'd be cleaning them 3 times a week instead of once.
I don't PLAN on using green wood and I know it's not efficient, but I have a couple tree services that give me wood, and if for some reason I HAVE to burn green stuff, I at least want that option. I'm not going for the most efficiency, I'm going for convenience and lower heating costs than that of the oil I now use. All my wood is free except for the labor I'll have into preparing it, and even if I achieve a high efficiency, I'm going to be using a minimum of 20 cords a year. When I'm doing that much wood, I don't think there's going to be a big difference in 20 or 30 cords in terms of labor involved. I'll actually be doing in excess of 100 cords as I'll be preparing it for 3 other friends on a processor that I'm building. I want to have a giant pile of wood that we can all draw off of when needed and it will be loaded into their trucks or trailers with a front end loader, like dirt.
Now for someone that might only go thru 8 or 10 cords a year and prepares it all by hand, yes, I can see the issue of high efficiency. But for the everyday user that most likely gets his wood for free and enjoys, (to a point!), messing around with cutting and splitting it, I don't see a 10 or 20 percent efficiency gain as anything substantial. To me, it certainly wouldn't be worth the extra cost of a gasser. I Want to have a OWB that I throw wood into and get heat out of. That's it! I don't care if I have to feed it once, twice or three times a day as long as it provides the heat I need and the oil burner isn't kicking on.
Boiler plate is heat rolled and formed and has a high carbon and manganese content.
If you plan on monster pile of wood plan on plenty of water and ice and snow as a given state of affairs.
The issue with firewood is handling and rehandling it; I cut my firewood to 12 inch lengths simply because long splits get very heavy and snow and ice becomes an issue because I burn 12 plus cords annually with burning coal.
High quality firebrick does two things, it absorbs the heat and sheds the heat back into the firebox which adds back the heat from the thermal mass of the firebrick.
An EFM coal stoker uses a bottom fed retort with a forced draft fan firing under the coal fire which feeds a huge amount of combustion air that can be varied in volume by regulating both the coal fed per hour and the amount of forced draft air volume in cubic foot per hour of air for combustion.
Fire tubes do two things, absorb heat from combustion and radiate it back into the water surrounding them if a hot water system is used.
The Tarm folks tell all the owners that the tubes must be wire brushed to be kept open while burning and the boiler has to be shut down to clean them.
The idea is that the more water you have to heat the more thermal mass you have to heat and shed back into the heating space and the residual heat that returns back to the boiler reduces the amount of heat needed to reheat it.
Lets say you have an 8,000 gallon surplus insulated railroad tank car that you purchased to store hot water for heating.
8,000 gallons of water weighs 8.34 pounds per gallon +-=> 66,720 pounds of water at 50 degrees of temperature. This 50 degree water is already able to absorb additional heat energy for you.
Just to round it off lets say you have 67,000 pounds of water at 50 degrees SO;
assuming you want to raise the the water temperature to 160 degrees for heating
you need to raise the 8,000 gallons of water 110 degrees to 160 degrees in a batch burn which is the most efficient method as the fire will get hot and stay hot until the 8,000 gallons of water is heated in one cycle.
It takes one BTU to raise one pound of water one degree in temperature.
In order to raise 67,000 pounds of water one degree in temperature it will
require 67,000 BTU
In order to raise 67,000 pounds of water 110 degrees it will require you to create 7,370,000 BTU of heat energy to heat the 8,000 gallons of water
SO lets say you use an EFM stoker burning slowly at 10 pounds per hour of anthracite its net BTU per hour rounded off is 75,000 BTU per hour.
It will require the stoker to burn 10 pounds per hour for 99 hours(rounded higher) to obtain the 160 degree temperature for cut off and idle. This is 990 pounds of anthracite coal burned in 99 hours of batch burning being 4 days and 3 hours.
This tank then has the useable heat energy in temperature of 160 degree's in 8,000 gallons of water to make domestic hot water and also heat living space.
SO lets say for simplicities sake you burn from October 1 to May 1 with a 24-hour a day burn with one stoker circulating 25 gallons per minute between the stoker, the living space and the storage tank(not including standby heat loss which will be minimal because the tank is insulated).
240 days burning coal through the stoker
24 hours per day at 10 pounds per hour
240 pounds per day times 240 days equals
29 tons of anthracite coal
During this time the stoker will have produced 432,000,000 Million BTU of heat energy for hydronic heating and domestic hot water in a shed or garage for your use no matter the heat loss.
The lowest setting for the DF520 is 7.5 pounds per hour which creates 56,000 BTU per hour of heat energy for your use. At this rate you would consume 21.6 tons of anthracite coal per season and would have created 322,560,000 BTU of heat energy for your use. Again the more hot water you have in storage the better.
Soft coal would cost less but you would burn more of it; BUT saying that a metalllurigical grade soft coal costs much less-2/3 less than good washed anthracite coal of any size
.
If you have hot water before the heating season your system will be better prepared for the heat load as the water is preheated and as it is closed system there is no water loss.
it all depends on your opportunity cost.
I do not remember the name of the member that feeds his boiler with a skid loader but I would chat with him via a PM about water storage.