The beauty of having an insulated surplus railroad tank car is that it is already insulated and you can simply set it outside without burying it and use insulated piping to and from the building. The hot water that you make has thermal mass and thermal mass is what gives you heat.
If you are are looking for a hot water heating method you should look at the
www.allcanadianheater.com as you can make 140 degree water you need to heat the new building.
You can make use of Western Sub Anthracite rice coal to make hot water or steam heat using a coal stoker boiler rated for making steam like the AHS S500 coalgun or the Axeman Anderson 130S or 260S The Axeman Anderson coal stoker boilers are already certified for steam heat in their design and price and they are very efficient. The Axeman Anderson coal stoker boilers are auger fed from a coal bin.
The AHS coal stoker boilers require the end user to purchase steam certification as an added expense in the purchase. The AHS coal stoker boilers have a hopper that gravity feeds the pea coal to the rolling coal grate.
An Axeman Anderson S260 coal stoker boiler has one 4 inch tapping to feed steam to a 4 inch drop header that can be set up with as many smaller diameter steam lines to feed dry steam to each radiator quickly venting air out of the radiators and allowing dry steam to enter each radiator quickly and quickly heating the radiator(s).
Hot water or steam radiators make use of electromagnetic radiation to quickly shed heat into a space requiring it.
In order for you to make efficient use of in floor heat you need to insulate the slab and the perimeter foundation of the building.
The issue is how much tubing you need and how close the spacing of the tubing is as you need in keep in mind that you have to keep the tubing six inches away from the edge of the slab. You also need to plan on heating the perimeter aprons of the slab as well to avoid having ice and snow build up on the aprons.
You can install the tubing 6 inches apart for the entire floor and end up having 20+ plus heating zones in the floor.
The biggest advantage of having dry steam as a heat source is that you can heat the entire building as one zone with a single thermostat and avoid requiring a huge number of circulators with a huge hot water header pipe and cool water returns back to a cold water header pipe with 20+ tapping's that could return the cool water to the boiler sump at less than 140 degrees Fahrenheit which is poison to a hot water boilers steam chest due to the lower water temperature.
A single steam boiler and a common header pipe in the ceiling feeding dry steam to radiators on the buildings perimeter using refrigeration grade copper tubing to feed the low pressure steam can make a lot of heat quickly using a coal stoker.
The thing you have to keep in mind that running the in floor heating system will be problematic at 160+ degree temperatures as the Pex will be under stress from the heat AND every time the door opens you lose heat that has to be replaced.
The in floor loops have efficiency limits of 250-300 feet per loop and each loop is a separate zone so you need to keep that in mind if you intend on heating the concrete entrance apron at each door.
Using a pellet boiler entails using 2 tons of pellets for every ton of coal as far as comparing heating fuels.
If my rough math is right:
if you use the 70 foot distance for the 6 inch spacing you have one heating loop for every 4 lines rounded and that makes 140 lines of tubing along the long side of the building making 18 heating loops-9,800 feet.
If you use the 54 foot length for each loop and six inch spacing you have 6 lines rounded for each 300 foot loop PLUS the feed and return line to each heating loop-324 feet for each loop. The 54 foot width makes 6 loops for 324 feet per loop making 23 heating loops.
your going to shed a lot of heat quickly and have cold water coming back to the boiler and water below 140 degrees creates a lot of oxygen which is bad for hot water heating systems.
A new very large building of any size lends itself to steam heat out of basic simplicity because you can hang radiators and have a single steam header pipe with cross connections from the header pipe to the radiators hung on the wall.
Another option is gravity hot water heat where the boiler makes 170+ degree hot water that rises to a single top fed header pipe that feeds the hot water to perimeter radiators and then back to the boiler sump.
The top fed hot water heating system does not require the system to be bled as there is no air in the system one it is filled. An open to air expansion tank is required to be hung in the ceiling above the boiler and no circulators are required to move the hot water water.
A coal stoker boiler lends itself very well to a top fed gravity hot water system in the case of the shop with no basement as the radiators can be placed along the long walls with the return lines behind the radiators back to the boiler sump. It is simple to design using a four inch vertical riser pipe to feed the common header pipe feeding the radiators with plenty of hot water feeding the radiators and the cooler return water returning to the boiler sump to be reheated and then enter the 4 inch riser pipe to be tee'd off to 4 inch header pipe s then 3 inch pipe and then 2 inch pipe and pushed through the drop feeder lines to the perimeter radiators and then returned to the boiler sump with smaller piping coming off the bottom of each radiator that is tee'd into the return lines(the number of return lines depends on how many doors are installed in the building but the radiators will push a huge amount of heat through them the by the simple use of electromagnetic radiation shedding heat constantly into the shop.
Once the boiler comes up to temperature with all that hot water you will have a huge amount of hot water shedding heat into the workspace and you can keep the shop at 75 degrees if you wish easily using one thermostat in the shop hung on the wall.