not recommend it for anything over 80,000btu or else a system that would always give you a temp differential of 30* or more. It works very well but it's designed for European sized systems which are smaller load and always used with a buffer tank in close proximity to the boiler. Hence....very low head.
I think the
bold parts are the really important things to note. Deep Portage with its Froling FHG L50 (170,000 btu rated), equipped with a loading unit (spec max flow at 11.5gpm) with a similar pump curve to the Caleffi, struggled with excessive idling, even boiler shutdown, and very poor performance. It had a 1650 gallon storage tank right next to the boiler. The solution ended up being simple and quite inexpensive, and now the Froling has become the Fraulein at DP. I would think the Caleffi also could provide excellent performance, even with a high output boiler, with appropriate design.
1) Use it as a loading unit for boiler to storage, not as a system circulator. Boiler/unit system output directly to (top of) storage and system return to unit/boiler directly from (bottom) of storage. This loop is independent of system demands, and all system demands are from storage (top) and returns to storage (bottom).
2) Always have sufficient capacity in storage to accept the output produced by a full load of wood. The substance of this statement is in the Froling manual.
3) On boiler firing, make sure that the temperature differential from storage to boiler output at the unit flow rate can move the full boiler output. This probably requires an initial temperature differential of at least 30* but probably more. It can be less as the wood load burns down and boiler output falls.
4) Really helpful in tuning the operation is using well seasoned wood of a relatively consistent btu content per load of wood, and then weighing what would be a typical full wood load to determine the btus that storage must have capacity to accept. Note the volume of that full load of wood, and future wood loads of similar volume need not be weighed.
DP Example (representative, DP actual operational rule has been customized):
5) Assume a full load of wood is 75 lbs. Heat content = 75 x 6050 = 453,750 btus x .9 (assumed boiler efficiency) = 408,375 btus net wood load heat content.
6) Operational rule: don't fire boiler unless middle of tank temp is 130F or less. Since the 130F water could (not likely though) extend to the bottom of the tank, and the temperature of the water from the top of the tank to the middle could be (not likely though) be 190F, the tank has at least 825 gallons of 130F water that could be raised to 190F.
7) 825 gallons of water with a 60F temperature differential (130 to 190F) has a btu acceptance capacity of 825 x 60 x 8.34 = 412,830 btus.
8) The acceptance capacity is sufficient for the btus of the wood load.
9) Assuming 1.25" copper pipe, 40 feet of equivalent length, the pump head is less than 3 feet. At 3 feet of pump head, the Caleffi unit will easily move 6 gpm or more. 6 gpm at a 60F temperature differential will move 180,000 btus, the full rated output of a boiler like the Froling. Boiler output will fall as the wood load burns down, and 6 gpm will be sufficient for the entire wood load without any boiler idling.
This example is very conservative and is only intended to show that a unit like the Caleffi can work well with a high output boiler with sufficient storage in close proximity to the boiler. In the real world and with both some operational experience for the boiler being used and storage capacity available, and using the math, a custom operational rule can be developed to allow use of a Caleffi or other loading unit and obtain very satisfactory results.
