Yours is outside (XT series?). Mine will be in the house (Elite 100).
Yours is roughly 2x mine, both in BTU and water jacket size.
My plan is very similar to the "big house" side of your set up, but with zone valves instead of pumps and a large buffer / storage tank where your (red and teal) manifolds are. This location will be an atmospheric tank, and will require more water treatment chemical due to the increased volume of water. Essentially making the boiler think it has a huge tank of it's own. Once the boiler comes up to temp and the LK loads it will charge the tank. As the tank heats, more BTU's will be available to the house HX's.
Good: Facilitates batch burns, especially helpful for shoulder seasons.
Bad: Since the Empyre's are designed to cycle on / off, too long of an idle cycle may cause the refractory to cool too far and prevent re-ignition when the blower turns on. If the boiler goes out, bridges, fails to re-light itself, runs out of wood, etc you will still have the boiler pump running, so it may rob BTU's from the tank and blow them up the flue. Some have rigged up a timer or low flue temp shutdown device.
Something small would be considered a buffer tank. You could put a buffer in each house. They would go in the pressurized loops of the (oil) system(s). They could be sized differently based on the heat load each house sees. You would most likely need to up-size whatever expansion tank(s)s are already there.
You could do one large or 2 separate atmospheric tanks, one in each house as well. They would go in the non-pressurized boiler loops. Properly sized for the whole load (one tank) or different loads (if using 2 separate tanks). I think for a 200K boiler and 2 houses, 1000 gal minimum would be necessary.
Atmospheric tanks will require water treatment if that same water will be pumping through the boiler. Chemistry control will be crucial since atmospheric tanks will contain more dissolved O2 due to the larger surface area of the air to water interface.
My plan:
Empyre Elite 100 w/ danfoss, pumped to an atmospheric tank. The boiler will be on a floor that is 3.5 feet higher than the tanks floor, so all air will vent out the boiler vent / float guage. Cap off the float guage hole. Plumb the overflow port @ the float guage to a stainless Crown Mega Stor 40 gal indirect that has a pinhole in the heat coil. Essentially the tank and boiler will be flooded 24/7 and the 1/2 dead indirect will serve as a head tank / cistern tank to take care of the expansion & contraction as the sysyem undergoes temp swings.
Taco ZVC 406 zone valve controller is the main brain. On a call for heat: The storage pump will suck from tank to warm the HX. The load pump and corresponding zone valve will satisify the load demand via the oil boiler headers. The cooler zone returns will be re-heated by the HX. 80 gal indirect will have priority, and be plumbed with a Nyletherm for summer use.
The "TT" contacts of the ZVC 406 will go to the storage aquastat, then to the oil boilers Honeywell 8124 tripple aquastat. If storage is hot, oil burner will be locked out via storage aquastat. If storage is cold, oil burner will fire and storage pump will be locked out. 8124 low limit will either be set to minimum 100 or disabled via interrupting the "blue wire".
Tank choices:
- New oil tanks, multiple 275's or 330's. Made of 12 ga mild steel. Only a few thousandths thinner than the 1/8" Empyre water jacket. That is all I can fit in my 14 x 14 basement without major cost and without knocking a wall out to get them in there.
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http://www.newhorizonstore.com/Products/96-tank-hot-water-storage.aspx Pricey for 500 gal. Made of 1/8 mild steel plate, same as the Empyre boiler jacket.
- Stainless steel or mild steel IBC tote tank. A refurbished, used, 550 gal stainless IBC can be had for 1/2 the cost of the New Horizons tank. Mild steel is 1/3 the cost. This would require knocking studs out of a load bearing wall to install. I don't forsee that happening.