Sugar Shack with RMH power source

Greetings to all! I'm pretty new on the forums, so redirect me if I'm not the first to try this or ask these questions.

I intend to build a sugar shack (for making maple syrup) with an RMH to do the boiling. I'm getting anxious now about getting it done before winter, but being on a layoff, I'm feeling optimistic about my chances (if the rain ever lets up). I primarily wanted to pop on here for questions about the foundation of the shack, but I know I have a good deal to learn about a good deal of topics, so feel free to hit me up with anything.

I've attached my floor plan for the shack, which will be about 10'x10' inside. Notes on the plan: RO is a reverse osmosis system in a 5 gallon bucket, which will be the first stop for the incoming sap. B1-3 are plastic 55 gallon drums that will rest on the bench and soak up some of the lowest quality warmth when heating. I intend to make a preheat pan out of stainless that will sit on the bench between the barrels and the bell. Here comes the innovation: I'm going to set up a little pump that will take from the preheat pan and pump it up 6 50' aluminum tubes (McMaster part number 5177K73) that will coil around the bell, leading up to the evaporator pan that sits on top of the bell. The tubing will serve as a heat shield, as it will cover most of the surface of the bell.

As far as the design of the shack, I assumed 4" thick walls and typical wood construction. With the moisture I'll be pumping out, I thought that earthen or cob type designs wouldn't be a great fit. Yes, I know that I'm planning to make the bench out of cob, but that's not what's supposed to let the humid out. I'll have panels/doors/windows to let in outside air and let out the steam. My biggest concern and question right now is foundation. This is tucked into a hillside, as you can see in the photos, but I live in Minnesota. How serious of a foundation am I talking, here? Continuous concrete with various depths (and what depths)? Separate foundation techniques for the building and RMH? Or can I make something easier/cheaper work that would survive the frost?

I've built a firewood shelf out of pallets next to where it will be that I'm rather proud of, which has 4 bays ~32" deep, a top shelf for kindling, a salvaged tin roof, and I'm planning on putting vented siding boards on it when I get the chance. And I put it on silo block from my neighbor's dad, which is roughly 9" thick and makes a great floor (unfortunately, there isn't much left for flooring or footings of the shack). I've got pics attached of this beaut, and the clay mound next to it that I will gobble up when making the heater mass.

-Benton

Hi Benton, Welcome to Permies;
Indeed, sugar harvesting using an RMH has been successfully done before.

About your new sugar shack, you might consider using brick over wood.
Here are a few posts about my outdoor kitchen.
https://permies.com/t/164923/rocket-ovens/Build-Black-White-Rocket-Oven
https://permies.com/t/166800/rocket-ovens/Brick-Outdoor-Kitchen

I had never built a building with brick before.
It is easier than one would think and the costs compared to wood are much more reasonable.
The finished product is there practically forever.
It would make a fine nonflammable sugar shack!

Hi Benton, so what size pan will you have?  

Having the metal barrel top of the bell under the pan will block a lot of the heat.  I much prefer to have the flames hitting the bottom of my syrup pan.  I'd be tempted to try to come up with a way to spread the flame from the top of the riser so it blasts the whole bottom of your pan.

Be careful with tubing wrapped around something hot like that.  It's really easy to accidentally over heat it (pump stops, siphon stops, fire is hotter than you thought, etc) and the sap boils to steam in that tube.  It probably won't blow anything up since the end is open but the flow gets spluttery.  I guess if you're pumping it through it might just push the steam out and keep on running.  I'd use a food grade pump.

My shack is 14' by at least that (it turns into a garage on one end) and it's a good size.  My boiling rig is a more traditional cinder block arch that is about 8' by 3'.  I think you might want your building to be a bit bigger.

How many trees will you be tapping?

Last winter I moved my evaporator into a 5' x 8' half-open shed, and had just enough space to operate it effectively. Sap storage was outside with bucket transfer, and wood storage was right next to the shed. The evaporator is about 30" wide x 4' long plus a foot of firebox feed on one end and chimney on the other end, sticking a foot out from under the roof.

You can comfortably fit a 29" x 29" sap pan like mine, or a somewhat bigger one, and sap storage in a 10' x 10' space. A rocket mass heater is not likely to give you the best results unless you plan a tiny sap pan. You want to blast the entire bottom surface of your pan with heat, and have strong draft for a big fierce fire. I use an 8" chimney pipe, and have an 8" wide x 9" high x 32" deep L-tube rocket firebox which can hold enough wood for a steady fire. I use something like 1/4 cord of wood to get around 3 gallons of syrup each year. Full description here.

Your RO setup is considerably more technical than I do; how much does it reduce the water volume? I am also concerned about the sap piping around the barrel, and its possibility of failure if the pump hiccups. I am not sure trying to heat a mass bench to heat the sap barrels is a good plan. I think having the sap barrels elevated above the pan and surrounding the chimney pipe, touching it if they are metal, would work better, starting to warm them immediately and not trying to store heat after the boiling is done. That would allow foolproof and less involved gravity flow.

I like your firewood shelf.
In response to your direct questions, I would recommend a single foundation for the evaporator. The shack can have pad or post footings and float on grade, as I don't think it matters that much if it heaves a bit.I also don't think you really need thick walls, just siding that keeps out wind. You will be generating radiant heat inside and changing the air frequently, so insulation seems sort of pointless. If you have access to old appliances, they can form the shell to contain the rocket workings very easily and cheaply, and need only four or so stone/concrete pads to support the corners. I built both of my evaporators in a matter of days each, in outdoor winter weather.

Thanks so much to everyone for the responses!
-The RO setup will take out half of the water, it's a primitive dial control to set the out flow rates equal ("clean" and "dirty," where I want the dirty). You can look it up under RO bucket. I might get fancy and put a drain pipe straight into a nearby manhole-sized drainage that predates me.
-Thomas, I'm curious where one gets good bricks for building for cheap. I saw 88 cents for a brick at Lowe's, which would add up awful quick.
-I was imagining a stainless pan on top basically covering the top of the barrel, with the tubes emptying into it. Also about the tubes, I was going to have them stand off about an inch from the sides of the barrel.

Some other slightly technical questions on foundations if any want to tackle it: Since the (block) base of the retaining wall cuts in close to the corner of the building, would it be okay to just kind of glob a lot of cement around the block in question and call it a good foundation? Also, I don't want to have a dirt floor, so how would I incorporate a wooden floor if I don't do a solid concrete floor? Do note that I marked off "pavers" around the feed area. These could go on top of the wood floor, I suppose, but I'd like to avoid trip hazards.

-Benton

I got mine at home depot @.48 each.
I would leave the floor dirt/ gravel to start.
Later as time and money permit, I would hand-pour small sections with a premix until eventually, the whole floor is concrete.

I can't see any stones in your pictures, but your landscape looks a lot like mine. Are there flat stones available in your area? If so, you can get a good start on a hard (non-muddy) floor with those and the pile of pavers I see. A layer of any sort of stones leveled off and filled with small stone/gravel if necessary will give a good base.

I wouldn't depend on blocks the size of the ones in the pictures to hold a whole corner of a shed. If you don't have bigger ones, I would get some small rebar or even any sort of wire mesh, fencing, whatever, and make reinforced concrete pads at least 16" square if not bigger. Glopping concrete around blocks will not be sturdy for the long run but will separate in probably a few years at most.

Even though in terms of heat transfer I like your  idea for the tube heat exchanger, in terms of the practicality, I’d advise against putting sugar-based food through fire-heated metal tubing, especially aluminum. 1) What if it burns?  It would be very difficult or impossible to clean and inspect for cleanliness or corrosion. 2) Sometimes aluminum can corrode, like with alkaline cleaners or common chloride-salts (remember Flint Michigan accidentally putting river water through metal pipes?). Stainless steel is more temperature resistant and is the standard for food and for maple syrup evaporators.

I suppose many of the issues with using aluminum could be avoided if it wasn’t carrying sap, but carried some other heat-transfer fluid like water or air.  

Note that finished syrup boils slightly hotter than water. If you wanted a water-based heat transfer fluid to be able to heat near-finished syrup, maybe you could add something to raise the boiling point.  Ideally it would be non-toxic, non-corrosive, and wouldn’t burn. I’m wondering about something like a 25% solution of “Sodium acetate” (The salt that results from mixing baking soda and vinegar).  And by cooking with a “double boiler” like this, it would help protect the valuable stainless steel (and the syrup too for that matter) from scorching high temperatures.