Caleffi thermo bloc

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huffdawg

Minister of Fire
Oct 3, 2009
1,457
British Columbia Canada
It likely would depend how well optimized your storage location & orientation were, along with piping in between.

My LK 810 is supposed to handle it in a power outage, but it won't handle it all. It might if my storage was taller. I use a dump zone, and also have a UPS on standby for the LK.
 
The ThermoBloc and other loading unit type devices need to be used with a good understanding of their hydronic performance. Notice the flow rates. At 8gpm Speed 1 the operation already is in the bottom fourth of the pump curve, and maximum flow is 11gpm at 1 foot of head. Not many systems would have head this low. Now imagine a 40 kw/140,000 btu boiler, delta-T at 20F. At this rate of output 14gpm is required to prevent idling, at delta-T = 30, 9gpm is required, etc.

At low to medium flow rates and high delta-T's these units can perform very well with any boiler, particularly with care given to make sure the wood load is well burned down, and output is low, when delta-T is low. Careful attention needs to be given to system design, including adequate storage, especially with high output boilers and lower delta-T systems.
 
The Caleffi is a great product but I would 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.

A laddomat or Honeywell mixing valve of the same type can also restrict flow when return temps from storage or the system are really low.
I watched a system powered by a 300,000btu Econoburn for a while back in November up at Michigan Tech's campus. The boiler protection valve was seeing return from storage at about 60* at start up and it bypassed practically everything back to the boiler trying to keep return above 140*. The boiler was cranking and in fact hit the high limit and shut down. All the valve "knew" was that return water was below 140* and it shunted 90% of the flow back to the boiler.

I'm a believer, especially in systems of 30KW and up, of a pumped bypass for boiler protection using one of the following methods.
1>bypass controlled by an aquastat so you get full flow one place or the other.
2> Injection mixing control between main boiler supply/return
3> variable speed pump sensing return temperature, ramping up as return temps climb.
 
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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.
 
Maple1, my head spins on this as I'm guessing your does too. But I think the short answer is that at 180,000 btuh, source water at 130F, and 6 gpm, DT cannot be greater than 60, and boiler output cannot be greater than 190.

And a longer answer. Assume 180,000 btuh, 6 gpm, DT of 60 (source water = 130, boiler output = 190), and 140 return via the loading unit/mixing valve. Since 6 gpm is leaving the boiler, 6 gpm must return to the boiler. If 1 gpm of 190 water is diverted through the mixing valve for boiler return, then 5 gpm would be moving directly to storage and returned from storage, where in the mixing valve that 5 gpm mixes with the 1 gpm diverted.

1 gpm of 190 water mixed with 5 gpm of 130 water in the mixing valve = average 6 gpm of 140F water being returned to the boiler [(5 x 130 +190) / 6 = 140]. Thus, a total of 6 gpm has been raised from 130 to 140, DT of 10, and 6 x 10 x 500 = 30,000 btuh. Next, that 6 gpm of 140 water still needs to be raised to 190, DT of 50, and 6 x50 x 500 = 150,000 btuh. Total boiler output = 180,000 btuh. Boiler output does not exceed 190.

I know there are forum members much more savvy than I am who might be able to either give a better explanation or let me know my logic has become illogical.
 
Yes, mine spins at times too.

Maybe I'm over simplifying - but if 140 is being returned, that means source = 140, and a 50dt thru the boiler. At 6gpm thru the boiler. I'm just looking at in & out temps of boiler, and flow there. So I get 6gpmx60min/hrx8lbs/galx50dt=144,000btu/hr boiler output. (Might be a rounding thing in there with the 8). Then looking at the storage side with that example, 5gpm to there at 60dt would be the same btu/hr - so I suspect there is more going around the bypass than 1gpm. My over simplification there would be 130 to 140 is dt10, 190 to 140 is dt50 - a 1:5 ratio x 6 = 1.2gpm around bypass.

Either way, my LK810 with a 15-58 on it will handle my boiler on low speed, maybe a 25dt. I don't think I'm running the boiler at full capacity, I rarely fill it full & my wood is usually a mix of hard & soft. I don't really know what GPM it is pumping at that. Tanks are close & 1-1/4" piping, but I have been guesstimating all along it's around 6. But, wrinkle time- it also gets an assist from my load pump (Alpha) when it's pumping, and it usually is pumping when I'm in the hottest parts of my burn, and usually to most or all of my 4 zones.

Which leads to more head spinning...
 
What I know for sure is that the method I described works at DP and it works on my Tarm, which has a known flow rate of 14gpm.
 
Would you still need a separate heat dump zone aside from your storage tanks if you were utilzing this caleffie thermo-block.

http://www.hydronicspecialtysupply.com/uploads/1/0/1/5/10157904/thermobloc_281_spec_sheet.pdf

Huff
Regardless of a valved or pumped solution you need SOMEPLACE for the heat energy to park or dissipate. Either the tanks need to have capacity to absorb an over fire condition, maybe by limiting them to 180 and allowing an over heat conditon to take it up to 190 or 200F.

Or a dump radiatior, zone, unit heater, etc.

One nice feature of the Thermobloc is the gravity gate, swing check, that allows over-heat circulation in a power outage condition. As Jim mentioned it needs to be piped to allow this thermosiphon and you need a place for the energy to go. Gravity circulation works best with large or low pressure drop emitters, like cast iron radiators. It may be tough to dissipate the boiler output through a few feet of 3/4 fin tube for example. The overheat device would thermosiphon best if located above the boiler, this is how un-powered thermosiphon solar systems operate.

Passive solar thermal systems are very common in warm climate areas across the globe. Most Chinese systems use evac tubes so there is some serious heat energy being transferred into the tank located just above the tubes.

Typically in a power outage the boiler output also decreases if it is a fan induced type gasifier. So you are not looking to dump a full fired, full fire box load.
 
I have a Tarm40K boiler, Termovar loading unit and a 1000 gallon tank a couple feet away connected with 1-1/4" and 2" piping. Very low head circuit with the bottom of the tank about 6" above the return connection on the boiler.

I have tested the thermosiphoning capacity at full burn with the return temp of the storage water at 110F. The deltaT shot up to almost 70F, supply temp to the storage tank about 180F. It idled along like that for half an hour or so when I was satisfied (bored) and plugged back in and went back to whatever it was I was doing.

So, it can work. HOWEVER... if the return water from the tank were coming in around 150F, (as it typically is on the second loading cycle), and I had a full load of wood cranking away, a power outage could easily make the basement steamy. I haven't done this yet but I was reminded of the possibility when I got home from work about 1am last night and didn't think before tossing in a full load of hardwood and touched it off. A bit later I went back to check and the return water was almost 150F and the supply out to the tank was 190F. Typical deltaT with the loading unit circulator set at the lowest speed. I began to suspect I was a little over-ambitious with the load of wood I put in there so I set the speed up to 3.

This would have been an inconvenient time for the power to go out if I were relying on thermosiphon alone.

I think the concensus is that it just depends. On lots of things.
 
I will see what I can add here as I use the 281 Caleffi loading unit that Huffdawg is inquiring about with my Econoburn 200. I seem to meet most of the requirements that jebatty is referring to. My storage is close to my boiler, the 281 only pumps from boiler to storage and back, with a separate Alpha supplying the load. The 281 pumps directly to the top of my tanks, not part way up as shown in my avatar ( I changed that) .The Alpha pulls from the top of storage and returns to the bottom. The bottom of my tanks are almost always around 95* when I start a burn and this doesn't increase until the tanks are about 80% charged. The flow through my tanks is very low as my Alpha only pumps about 1 gpm so I get lots of stratification.
To address Huffdawg's question - I have had the power go out but with the gravity gate opening in the 281 I seem to get enough thermosiphon through the boiler to take care of things, as the 95* in the bottom of my tanks is being pulled through my boiler and cooling things down. I would not usually have a large load in the boiler near the end of my burn when the temp in the bottom of the tanks is starting to increase. Also, once the fan turns off my boiler seems to shut down the fire fairly quickly. My piping is 1.25 inch copper. My tanks are 9 feet high and my boiler is 5 feet.
I suppose that is the good part of having good stratification.
To address more of what maple and jebatty were discussing, I think I have about 4 ft of head in my system from boiler to storage so at pump high speed I can pump about 7-8 gpm. This seems to work for me. I stay with fairly large chunks of wood in my boiler to keep a longer and cooler burn. I set my boiler top temp at 190 but most of my burn is in the 165- 175* range. The boiler might idle if I fill it full of good maple and oak but I manage that by mixing in some elm or other wood with less btu's. Either that or just put less in.
I think the biggest problem that I have now with my system is that the large stratification that keeps the bottom of my tanks cool until the end of the burn means I use more of the btu's created by the boiler to mix back into the return water to get it up to 140. For example, if I am creating 170* water out the top and bringing 95* in the bottom, I am sending about 4 out of the 7 gallons that I am flowing in total back around the boiler loop just to maintain the 140 intake temperature. That only leaves 3 gallons of hot water going to storage every minute. Do you guys have a solution for that one?
 
I think it's 6 of one, half dozen of the other.

If all of your hot water was going to storage with 95 coming back to the boiler, it would take many more laps to get your tanks heated up. Rather than one with the mixing (or two depending how hot you charge to). So the first lap with a 20dt would get you 115 out of the boiler. Next lap would get you 135. Next lap would get you 155. Next lap 175. Give or take. And you wouldn't get hot water to your loads until a few laps in if your storage is depleted. I'm good with one lap with hotter water coming out but not as fast through storage.

My first lap gets me 165 or so, then I usually do another half lap. My first load of wood is usually a good one, the reload is a half load or so. I try not to go more than 185 or so out of the boiler, then I don't have to worry about overfiring or thinking heavily about exactly how much wood can I put in on this last load without tripping my dump.
 
Just seems like I am not getting btu's to storage very efficiently when 40% of my boiler output is going directly back in the boiler to maintain the 140 intake. If my EBW200 is suppose to be 87% efficient, I am knocking that efficiency, in getting btu's to storage, down to about 50%. Would it be worth investing in a larger pump? If I could move the flow to 12 gpm and maintain the same 170 out the boiler, I would be moving almost twice as many btu's to storage in the same time. I guess the question then becomes, can I maintain the 170 at the higher flow rate? At temps of 170 out and 95 in I am always losing 40% back to the boiler regardless of how many gpm I am flowing.
 
I know this is confusing, but I don't think you understand what your boiler is doing. All of your boiler output, adjusted for efficiency, is going into your storage tank. Your boiler is rated at 200,000 btuh, and you say it is supposed to be 87% efficient, which means that boiler available output is 174,000 btuh maximum. Normally maximum output is only during the high burn portion of the load of wood. My rule of thumb for average output is about 75% of available output, meaning that a wood load will average 174,000 x .75 = 130,500 btuh available output. And that's it, that's all that is available, and really none of that (except nominal efficiency losses) is lost in going back to the boiler. In fact you likely are gaining by the return to the boiler because it is probably a certainty that your boiler will operate more efficiently with 140 return water than with cooler water.

At temp of 170 out and 95 in, the flow rate to move your entire boiler output on average only needs to be 130,500 / 500 / 75 = 3.48gpm. At full output of 174,000 btuh the needed flow rate is 4.64gpm. And since you can maintain 170 output with 95 input, and your output does not rise to the point of idling, it appears that you have an adequate flow rate. A bigger circulator will not help in the situation as described.

If you increase the flow rate, your average temperature output will drop. If you decrease the flow rate, your average temperature output will increase. The total btus will not change. You can't get any more heat out of your boiler than it can produce.
 
I think the biggest problem that I have now with my system is that the large stratification that keeps the bottom of my tanks cool until the end of the burn means I use more of the btu's created by the boiler to mix back into the return water to get it up to 140.

Maybe, or maybe not, my recent musing about my pellet boiler could be helpful. I am thinking of locking out the tank, which also commonly gets to 105* at the bottom, when the boiler is running and not up to temperature. My thought, like you, is that the return water is very cold at the beginning and needs to be mixed for a long period of time, and for me, my Caleffi is a 130*. I could use higher temperature faster.

Even though I have a 2-pipe (vs 4-pipe) tank setup that allows the zones first crack at the hot water, return water is still mixed with the cold tank bottom water, more so with only one of the two zones running, but even some with both zones running.

My current thinking is to put in a motorized mixing valve on the tank to maintain the loop at a higher level with excess heat going to the tank. I don't see why you cord wood guys couldn't do something similar.

I'm still trying to figure out a piping schematic. My 2-pipe setup might be more complicated than (I assume) your 4-pipe, with check valves required and all.
 
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Yes. I see what you are saying exactly. All the heat has to go somewhere. One of these days maybe I will be able to understand what my boiler is doing. But what can you expect? It's only been two years. ;lol
Thanks for setting me straight.
 
I might have made a mistake, but it doesn't really change much. Your boiler's rating at 200,000 btuh may be after reduction to 87% efficiency, not before. I'm not sure how the rating is determined.
 
Yes. I see what you are saying exactly. All the heat has to go somewhere. One of these days maybe I will be able to understand what my boiler is doing. But what can you expect? It's only been two years. ;lol
Thanks for setting me straight.


The primary job of the mixing valve used as boiler protection is to protect the boiler. Ideally with the correct sensor temperature range it should only bypass enough flow(or BTUs) to blend the temperature to protect the boiler, the remaining flow GPM, BTU, however you want to identify that, goes to the system or storage.

So you are not really wasting or diverting useable temperature, just sipping enough to assure that return temperature. ALL the boiler output goes somewhere one of those tow "loads"

I tried a few different sensors and found the 115° work best for me. It takes 18° above the 115° to shut bypass 100% So at 133° my bypass is completely shut down, 100% flow to the system and 133 at the boiler return. I can confirm this with the flow indicators I have at all 3 ports on the valve and also watch the flow rate modulates temperatures increase or decrease.

There really is no way to trick, or game the system, or speed it up, for that matter.

This could be done with a motorized valve also, like the Johnson Controls motorized valve. But you need a valve, operator, and control to drive it all. At the end of the day more $$ and complexity for the same result.
 
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So you are not really wasting or diverting useable temperature, just sipping enough to assure that return temperature. ALL the boiler output goes somewhere one of those tow "loads"

If your return temperature is 100*, you're going to more than sip, no?

How long will it stay at 133, if it gets that high, while the tank bottom is still cold? Why not a mixing valve on the tank? You get a 20* rise, that'd be 155 supply, which is low for me. I'm thinking it stays at 115 for a while if the tank bottom starts at 100.

Just thinking
 
In fact you likely are gaining by the return to the boiler because it is probably a certainty that your boiler will operate more efficiently with 140 return water than with cooler water.

I'm not so sure about that part? I think you would scrub more heat from the outgoing gasses, the cooler your boiler is. So would gain some efficiency with lower return temps. But the catch is we need to keep them above 140 to avoid creosote condensation issues.
 
The easiest solution is not to deplete the tank to such a low temperature. Burn the boiler when bottom of tank drops to 130*, for example. If your pump head is such that you still can move 7.25 gpm, you should do fine. With an initial differential of 55* (130 return and 185 supply), that's all you need to move your full boiler output at a supply temp of 185*: 55 x 500 x 7.25 = 199,375. As your wood load burns down, return temp will rise from 130* but btuh output will fall, and the 7.25 gpm probably will handle the burn OK. Give it a try, and if you don't like 130*, pick your number.
 
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