# Garn Stratification vs. Homogenization



## gregwhs2000 (Feb 14, 2015)

I've read a lot of the threads on this board about stratification with a Garn.  I think I understand the concepts pretty well and I know that during the off-cycle the water stratification is your friend.  It keeps the hottest water in your supply while the coolest stays in the bottom of the tank.  I understand that the cold water rolls upward during the firing cycle, although I have noticed the amount of cold water being returned while firing seems to greatly affect the amount of water homogenized by the roll.  The more cold water returned during firing, the less the roll seems to homogenize the tank.

So my issue is this unwanted stratification during the burn-cycle.  I've noticed that one or two Garn owners have went so far as to install a mix loop to activate during a burn-cycle so that they can maximize the total BTU storage by homogenizing the temperature of the water in the tank during the burn cycle.  I'm wondering if this is something I should consider?  I try not to take the controller temp above 190* or so, but it really bothers me knowing that so few gallons of the total tank are at that temp.  I would really love it if I could get the entire tank to an even 185* or so.

In my situation, I'm using only a water to air exchanger to heat my home this winter.  By next winter I will add about 2000SF of retrofit under-floor aluminum plates, and some radiators and I expect to have less of an issue with water temps.  But even at that point, I can't help but think it's a major advantage to be able to homogenize the tank temp during firing.

Can someone with some hands-on experience with using a mixing loop post some comments?  I'd be curious to know the details on how you installed your loop, what size pump you use, etc?  I'm also wondering if you feel it was worth the effort?


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## S.Whiplash (Feb 14, 2015)

If Garn thought that a mixing loop was beneficial they would have incorporated it into the design.  Stratification is desirable at all times so that the supply water can be used within minutes of firing to generate the useable btu output siphoned off the top of the tank.  By mixing it with the cold water at the bottom you would need to wait for the entire 2000 gals. to come up to a useable temperature which might take an hour or more.


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## gregwhs2000 (Feb 14, 2015)

S.Whiplash said:


> If Garn thought that a mixing loop was beneficial they would have incorporated it into the design.  Stratification is desirable at all times so that the supply water can be used within minutes of firing to generate the useable btu output siphoned off of the top of the tank.  By mixing it with the cold at the bottom you would need to wait for the entire 2000 gals. to come up to a useable temperature which might take an hour or more.



Not sure I agree with the opinion that Dectra has exhausted all the possible design improvements that can be made to a Garn and therefore homogenization is a bad idea.

I'm proposing a method to homogenize the tank once the lowest temp at the bottom is already acceptable for use as supply ... but the temp at the very top has reached the 190* mark that you are advised not to exceed.  If a big pump were to homogenize the whole tank at that point in time, firing could continue and a rather large amount of additional BTU's could be stored while all the water in the tank is still well below 190*.

I'm not saying this would  be a good idea for everyone with a Garn.  It may not even be worthwhile for my situation.  I just wanted to gain some insight from someone who has already done it.  All comments are welcome though.


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## TCaldwell (Feb 14, 2015)

I did it 2 years ago and believe that my 4 temp sensors indicate it was worth while. Without it the size of the wood load and starting temp decide how much turnover occurs on it's own. It's common to start with a 40+ degf , within 15 minutes into a burn it's within 5 degf till end of burn. As a drop in supply temps, it doesn't happen as your firing rate outstrips you demand exponentially. My mix loop is comprised of 1.5 inch bi, 2 nipples welded into the top of the tank, one towards the front low pulling up cold water and one towards the rear, about 8 inches below the water line discharging. I used a 0011 and a caleffi dirt cal in line. Not sure what the gpm is, the 0011 is energized from the same circuit as the blower motor. I have heard of some incorporating into the existing supply and return lines. If you decide to go through the top, I think a company called rhino makes high temp bulkhead fittings that are water tight. Running the pump in the other direction works also.


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## ewdudley (Feb 14, 2015)

TCaldwell said:


> first registered garn on hearth, first o2 controlled garn anywhere



If Garn thought  O2 control was worthwhile they would have incorporated it into their design long ago.  Lack of O2 control is desirable at all times because Dectra has not decided to do it.


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## gregwhs2000 (Feb 14, 2015)

TCaldwell said:


> I did it 2 years ago and believe that my 4 temp sensors indicate it was worth while.



I'm wondering if this could be engineered somehow with a modified man hole cover?  Or do you think it's that important that the high/low ends of the black iron be further apart?  Just thinking about the least drastic method to get a loop in-place.  I know from reading here that you've thrown caution into the wind long ago as far as hesitating to make mods ... I'll probably never get to the same level of expertise and confidence. 

So I guess the advantage of the bulkhead fittings is that they would eliminate the need for welding?


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## jebatty (Feb 14, 2015)

Stratification vs mixing has a lot to do with what your system usable or needed temperature is. If your demand is all low temperature radiant, then there is little or no benefit to stratification because you have to mix down to the radiant supply temperature. For example, for my in-floor pex I supply at 100F. So long as the supply from the tank is above 100F, all is good. Stratification does not help at all. In fact supplying at a higher temperature also returns higher temperature water back to the storage tank from the mixing valve, and this works to reduce/eliminate stratification.

With regard to the Garn, mixing will depend in large measure on the circulator flow rate through the Garn. At DP with the Garn WHS 3200, the circulator flow rate is 69 gpm. Mixing is extreme. System usable temperature can be as low as 140F and maximum target temperature, depending on outside temperature, is about 165F. The Garn is burned to as needed to maintain the desired supply temperature.


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## TCaldwell (Feb 14, 2015)

yes the bulkhead fittings would eliminate welding, my four temp sensors are surface mounted equidastant on the boiler front. Before a burn I add them up, divide by 4, giving the average water temp before mixing. This allows for easy calculation of wood needed to reach 185degf for example.


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## maple1 (Feb 14, 2015)

S.Whiplash post: 1900238 said:
			
		

> If Garn thought that a mixing loop was beneficial they would have incorporated it into the design.  Stratification is desirable at all times so that the supply water can be used within minutes of firing to generate the useable btu output siphoned off the top of the tank.  By mixing it with the cold water at the bottom you would need to wait for the entire 2000 gals. to come up to a useable temperature which might take an hour or more.



Do you have a Garn?


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## heaterman (Feb 14, 2015)

ewdudley said:


> If Garn thought  O2 control was worthwhile they would have incorporated it into their design long ago.  Lack of O2 control is desirable at all times because Dectra has not decided to do it.




Not necessarily EW. The added cost would be a significant factor in a boiler that is already at the upper end of the price range. 
Worthwhile from a clean burn standpoint.......maybe.
Worthwhile from a cost/benefit standpoint........not so much.


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## jebatty (Feb 14, 2015)

> Before a burn I add them up, divide by 4, giving the average water temp before mixing.


I've done the same thing to get a good estimate of the average. This calculation of  "average" can be off by a fair amount, however, unless the tank is being mixed well during the loading. With my horizontal 1000 gal tank, and loading storage only, no system draw and no mixing, the stratification line is very distinct as it moves down the tank. I would assume the same on a vertical tank. This can result in the bottom sensors reading quite a bit lower than the hot stratification line just above the sensors. For example: T - 190; M1 - 190; M2 - 185; B - 140; average is 176. But the M1-190 water may be just above the M-2 sensor, and the M2-185 line may be just above the B sensor. The actual average may be much closer to (190 +190 +190 +185) / 4 = 189. Not a deal killer, but need to be conscious of how the stratification line moves in the storage tank.


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## TCaldwell (Feb 15, 2015)

Curious if the garn tank shape and size affects natural turn over, my 1900 is basically rectangular with 45 degree corners, not too much different than a jr. I'd think the round style might turn over better. I'm not promoting my changes, but sometimes they do get noticed such as the turbulator!


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## maple1 (Feb 15, 2015)

heaterman said:


> Not necessarily EW. The added cost would be a significant factor in a boiler that is already at the upper end of the price range.
> Worthwhile from a clean burn standpoint.......maybe.
> Worthwhile from a cost/benefit standpoint........not so much.


 
You may have overlooked a subtle zinger in that post.

Or maybe I mis-saw one.


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## TCaldwell (Feb 15, 2015)

It was not missed, however Steve's point is well taken as he's a Dectra rep, and not about to jump on the train unless it burns pellets. The garn still holds a good market due to its design and always will. All of mods, o2, turbulator and mix loop though not part of the garn philosophy, still pique a viable interest. It's all good!


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## maple1 (Feb 15, 2015)

Yes, I think a lot of us play with our boilers & have made some improvements in their operation using things not incorporated in the original design - and just the fact that they weren't incorporated in the original design does not mean they were not worth doing or do not provide a real benefit. It's a pretty minor mod/add, but I keep replacing the fireplace grating over my nozzle that keeps burning up, I have convinced myself it's worth doing - not sure if they considered something like that at the Varm factory or not, it does look kinda Red Green. 

(The nozzle liner/overlay thing is another item that seems to be a pretty popular try - an easy one to play with, and I think with real benefits. Could go on likely...)


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## flyingcow (Feb 15, 2015)

Red Green=duct tape.  In a nozzle?


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## maple1 (Feb 15, 2015)

Red's a pretty diversified guy - he's so much more than duct tape. lol...


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## varadhammo (Feb 15, 2015)

I have my Garn set up with a mixing loop. I dropped a string of five ds18b20 sensors into the tank at the manhole cover, sensors are every 16" from bottom to top of tank (the bottom sensor about 1-2" from the bottom, top about 1-4" from top of water level (depending on tank temp). I wanted to check out the stratification/mixing behavior. Most of the time the load is drawing a low gpm from the Garn (radiant floors). The mixing pump is an Alpha, which reports 13 gpm. I have found in my case that the Garn does not mix well unless it's being pumped. This seems to run contrary to others' experience, and I'm not sure why.

Here is one graph I saved. You can see that the firing starts with the very top of the tank at 171F, 16" down (approximately supply level) it's 164F. The mixing pump is OFF (wanted to see what happened). So midway through the firing, the top of the tank reaches 208F (boiling here at 1900' elevation) while the middle levels continue to climb. So the top is boiling away while the middle is still pretty cool, and the bottom is cold!. At this point I turned on the mixing pump. Within about 20 minutes, the tank is mixed, and the top begins to drop slightly while the rest of the tank continues to charge. (The spikes on the bottom sensor you see after that are probably one of the larger zones turning on & off. Then when the bottom sensor drops to ~90F and stays there, that is when I turned the mixing pump off at a little after 6AM (I still have to rewire some things to turn it on/off with the blower fan.)

The second graph shows an entire charge/discharge cycle with the mixing pump on (at present the "mixing pump" is actually the GARN primary loop). You can see that there is a layer of water at the top of the tank which is somewhat "stranded" (stays above the supply tapping and doesn't get mixed down even with the pump running). Maybe pumping more gpm that top layer would get disturbed, but with my 13 gpm (pumping from supply to return tapping) it doesn't really get touched.


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## varadhammo (Feb 15, 2015)

Here is another version of that first graph but showing the flue temperature plot as well.

Edit: Just noticed that these don't show up with a white background for some reason, I guess the PNG has alpha transperency. Anyway if you can't see it, right click and view image in new tab.


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## varadhammo (Feb 15, 2015)

jebatty said:


> For example, for my in-floor pex I supply at 100F. So long as the supply from the tank is above 100F, all is good. Stratification does not help at all. In fact supplying at a higher temperature also returns higher temperature water back to the storage tank from the mixing valve, and this works to reduce/eliminate stratification.



I don't understand how this would be the case; doesn't the return temp always = system return temp? AFAICS, only the flow rate would change based on the storage temp (I'm assuming you're talking about a thermostatic mixing valve, and not a fixed ratio valve).


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## TCaldwell (Feb 15, 2015)

Good conclusive evidence supporting the garn mix loop benefit of tank charging, what model and water capacity is your garn?


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## varadhammo (Feb 15, 2015)

Garn WHS2000.

Also, I did speak with the good folks at Garn and it was indicated that they are playing with the idea of making a mix loop and sidestream filter setup standard at some point...


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## jebatty (Feb 15, 2015)

> I don't understand how this would be the case; doesn't the return temp always = system return temp? AFAICS, only the flow rate would change based on the storage temp (I'm assuming you're talking about a thermostatic mixing valve, and not a fixed ratio valve).


 Surprised me at first also. Assume 175F supply temp to the mixing valve from storage, mixing valve provides 100F to the in-floor pex, pex return temp is 70f. That means that 70F pex return is mixed in the mixing valve with 175F supply to bring the temp down to 100F. It also means that some 175F supply water is being returned to the storage tank. Stratification in the storage tank is immaterial so long as the tank can supply 100F water. 

Also, supply from the tank is drawn from the top and return to the tank is to the bottom via a diptube. That means that the tank is constantly mixing, and stratification is greatly reduced. If the tank draw continued long enough, the tank would mix to a relatively uniform temperature.

Keep in mind that in my system the 1000 gal storage tank only supplies the in-floor pex. There are no other draws on storage.


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## eauzonedan (Feb 15, 2015)

I have been planning just that addition this spring.  I often have a 40+ degree stratification between the top of the tank and the bottom as I get close to time to light a fire.  I've got three webrelay sensors in there plus the one for the controller and be advised the temp readings on the controller do NOT tell the whole tale.  Mike at Precision indicated a by-pass filter would be a good idea for my 1500's boiler water.  I wanted to wait till spring to pull this off, but my idea is to run a circ/filter  loop from one of the bottom drain ports up to the electrical ports near the top of the tank.  I would try pulling power for this pump off the duplex outlet for the fan so it would only circ while I was pumping heat into the beast.  I do not want to circ otherwise as in my situation more stratification - is a good thing when drawing heat out.  It is however a bad thing if recharging as I can't get the full btu load stored.  I kicked this around with Karl at Northwind and he suggested I consider pulling off the top and discharge to the bottom......opposite pumping direction of my original thought.....something still in play.  Your thoughts would be welcome. I was also going to fly this by the big guys at Dectra before I started down this road.
Dan


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## TCaldwell (Feb 15, 2015)

varadhammo said:


> Garn WHS2000.
> 
> Also, I did speak with the good folks at Garn and it was indicated that they are playing with the idea of making a mix loop and sidestream filter setup standard at some point...


What a surprise!


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## gregwhs2000 (Feb 16, 2015)

Awesome graphs varadhammo !!  I think they confirm the same things I've been suspecting in my new 2000 model.  It's been frustrating to see so little of the 1840+ gallons at my target temp and means more frequent firings while I have only water to air exchange in use this winter.

Not sure how soon I can get to it, but I'm definitely adding a mixing loop so that I can eliminate that thin top layer of the hottest water sitting above the supply inlet.  I think I will put the input of the mix loop about 5 inches below the water level and pump down ... probably to about 6 inches or so off the bottom.  I'm still thinking of just making a new manhole cover and extending the loop through it, rather than draining the tank and welding in new nipples.


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## Karl_northwind (Feb 16, 2015)

eauzonedan said:


> I have been planning just that addition this spring.  I often have a 40+ degree stratification between the top of the tank and the bottom as I get close to time to light a fire.  I've got three webrelay sensors in there plus the one for the controller and be advised the temp readings on the controller do NOT tell the whole tale.  Mike at Precision indicated a by-pass filter would be a good idea for my 1500's boiler water.  I wanted to wait till spring to pull this off, but my idea is to run a circ/filter  loop from one of the bottom drain ports up to the electrical ports near the top of the tank.  I would try pulling power for this pump off the duplex outlet for the fan so it would only circ while I was pumping heat into the beast.  I do not want to circ otherwise as in my situation more stratification - is a good thing when drawing heat out.  It is however a bad thing if recharging as I can't get the full btu load stored.  I kicked this around with Karl at Northwind and he suggested I consider pulling off the top and discharge to the bottom......opposite pumping direction of my original thought.....something still in play.  Your thoughts would be welcome. I was also going to fly this by the big guys at Dectra before I started down this road.
> Dan


 
My thought on that front was to stir up anything that might have collected in the bottom of the tank and collect it in the filter assembly, as well as mixing the tank.  
karl


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## gregwhs2000 (Feb 16, 2015)

I've noticed mention of by-pass filters, sidestream fitlers and the dirtcal that Tom has installed.  Are these all variations of the same thing or are there differences according to the type of application?


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## varadhammo (Feb 16, 2015)

I believe bypass and sidestream are referring to the same idea, which is that, rather than putting the filter inline with a system supply or return, you put it in a "sidestream", i.e. a parallel piping path to the main system path, and divert some flow through it using, say, a partially closed ball valve or other flow restriction. Since there will be a small flow through the filter whenever the system is running, over time all the system water should get filtered (at least in theory). In any case, the idea is to keep the filter out of the main line so that even if the filter isn't maintained/cleaned, it won't begin to interfere with the proper functioning of the system. Sidestream is also relatively easy to retrofit, you can cut it in pretty much anywhere.

According my conversations with Chris Holley, a dedicated mixing loop is also an ideal location for a filtering setup, since it also won't interfere critically with the heating system's functioning if it becomes clogged, etc. If you pump say 15gpm, you should get all 1830 gallons in about 2 hours. So two passes per firing, sounds fine.

There are several options for filter types. For a sidestream type, Chris suggested a stainless canister + spun cartridge filter, 5 micron. The Dirtcal is a Caleffi product, it is a vortex type separator (doesn't use a filter media, creates low velocity vortex which drops the dirt to a chamber in the bottom). The Dirtmag is a version with a magnetic separator which is good if you have ECM circs. My understanding (please correct me if I'm wrong) is that these vortex-type separators don't work as well with a very low flow rate, so might be less ideal for a sidestream type setup, and more ideal for a inline mixing loop application. I have a 1" NPT Dirtcal which they spec for an optimal max flow rate of 9.3gpm. If you go up to a 1-1/4", that is 15.3gpm. In my experience with the Alpha pumping 13gpm, it is enough to provide good mixing for the Garn (although it still doesn't disturb the topmost layer above the supply tapping).

One idea that just occurred to me is, if you pump from the bottom to the top, you could drop straight into the top of the tank and just let it splash down. Not sure how this would work, pumping an open loop like that, you'd probably need a foot valve at the intake end to keep the pump primed. And I don't know if the regular wet rotor circs can do that, esp. with 190 degree water they might cavitate running them in suction like that. The advantage would be that you'd be mixing into the very top of the water level regardless of the tank temperature (the level goes up and down probably about 3" from 120F - 190F).


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## eauzonedan (Feb 16, 2015)

Greg. My 1500 sat a couple years before it got installed and am therefore unsure of your exact configuration. I have bottom drain points both front and back. I valved both of these to allow two hoses to gravity drain. This gives me a 3/4 connection point on the bottom front without draining the tank down. I mis- spoke yesterday and noted the electrode ports when I should have said the three former analog thermometer ports for the other connection. These should be accessible without draining more than about 10 - 20% of the tank to get a valve in as mine are currently plugged.  It would be be a ton easier than pulling out the smoke wrench and look to be about prime locations. I was thinking to put the pump and by-pass filter on the front and just plug the pump into the controler duplex outlet   Another possible connection would be what they call the solar connection on the manhole flange. Drop a 90 on it and a short piece of pipe and continue to use your lid etc

Where in IL. ? I bailed from Aurora a year + ago

Dan


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## gregwhs2000 (Feb 16, 2015)

Dan.  My 2000 has only a front drain plug.  I did use a plugged tee on the return piping in the back, but did not valve it so that was dumb.  I do have a valved nipple on one of the old analog ports you referenced.  I could just connect the front drain to it, plus a filter and pump as you have suggested.  But I have two concerns ... one, the flow is only 3/4" which is not ideal ... two, the analog port may not be high enough to disrupt the stratification at the very top.  I suspect that few inches of stratification will be stubborn to eliminate without getting higher.  Got a link on the solar connection you referenced?

I'm downstate a bit from your old residence ... Effingham.


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## eauzonedan (Feb 16, 2015)

gregwhs2000 said:


> Dan.  My 2000 has only a front drain plug.  I did use a plugged tee on the return piping in the back, but did not valve it so that was dumb.  I do have a valved nipple on one of the old analog ports you referenced.  I could just connect the front drain to it, plus a filter and pump as you have suggested.  But I have two concerns ... one, the flow is only 3/4" which is not ideal ... two, the analog port may not be high enough to disrupt the stratification at the very top.  I suspect that few inches of stratification will be stubborn to eliminate without getting higher.  Got a link on the solar connection you referenced?
> 
> I'm downstate a bit from your old residence ... Effingham.



Greg:
Compared to up here you should be in a tee shirt and shorts down there! 

What they somewhere refer to as the solar connection in some Garn manual is on the vertical portion of the flange that supports the manhole cover.  It's on the outboard side of the flange at it's tallest point and is far enough below the manhole cover to allow a (horizontal) pipe to be threaded into it, and still get the manhole cover on.  I am currently using it to run wires to my weblink thermometers.  It is only a 3/4 hole - so it may not have the capacity you desire.  Should be 3/4 straight thread and I believe it's long enough to use it as a bulkhead fitting and run 3/4 pipe into if from both sides. Unsure what kind of gpm we could get thru 3/4 at short runs like this and if it would give the filter thru-put to make Mike at Precision happy or enough mixing to keep that part happy.  fyi he will supply the by-pass filters per my conversation with him last fall.  This whole deal was on my back burner till after heating season and I was going to dig into the detail stuff in the Spring.  Keep us posted how/when your fix proceeds.  The more I think about it - my rear 3/4 hose drain is off a tee back there on the main boiler return run.  Karl did my design and hooked that plumbing up back there.  It *does* have a second dedicated valve to speed up the draining process.  Pretty slow if only using garden hose as you must have discovered - and two is better than one.....  If I did that very often there would be a pump involved!!
Dan


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## BadgerBoilerMN (Feb 16, 2015)

You would save more energy by mixing on ODR, more especially when you get some low temperature radiation in place.


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## gregwhs2000 (Feb 16, 2015)

BadgerBoilerMN said:


> You would save more energy by mixing on ODR, more especially when you get some low temperature radiation in place.


Understood.  But does not really have any correlation to the topic of maximizing the BTU's stored.  Even after adding low temp heat radiation, it's still going to be a benefit to store more BTU's in the same water ... and with fewer burn cycles.


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## gregwhs2000 (Feb 16, 2015)

eauzonedan said:


> Greg:
> Compared to up here you should be in a tee shirt and shorts down there!



Sometimes ... but not the last few days!!

I'll give a second look at the 2000 on my next trip out there, but I don't believe it has the solar connection.  My manual says it's an option and I did not specify it.


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## gregwhs2000 (Feb 16, 2015)

eauzonedan said:


> and if it would give the filter thru-put to make Mike at Precision happy or enough mixing to keep that part happy.  fyi he will supply the by-pass filters per my conversation with him last fall.



What's going on with your water?


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## eauzonedan (Feb 16, 2015)

I sent in my samples last Fall as required and all seemed fine.  After a few days of running I saw a light "flock" in the tank   Looked kind of like a deep space picture of some kind of gas area in outer space.........very light matrix kind of thing and no real structure.....almost like a filament or cob webs.  I discussed it with Mike at Precision and he said it was the result of the chemicals doing their job and wiping out whatever was there.  No cheap way to know exactly what they were attacking, but they were working as designed.  Long term I may wish however to go with a filter to remove the "dead bodies" of whatever it was.  Those could build up over the long haul and cause me a long term issue if they piled up.  This also meshes with what Varadhamo got from the Garn Guys and noted in his previous post. I started by looking at where I could easily plumb the filter system up and the light bulb came on that it may help me knock down some of my stratification issue at the same time if I did it right.  I didn't want to pull the boiler off line and run on my LP backup - so I shelved the project till spring.

I just looked at the new latest and greatest manuals.  Great job, but a bit late for me......... I just had an issue with my damper freezing that I could have avoided as when I stuck it in - no such info was available last fall.........day late and a buck short....  The new manual doesn't look to make any reference to the solar connection any more, so maybe that has now gone away.  I purchased my unit a couple years ago when the steel prices were headed up and it sat a couple years.  It was right at the transition to the new controller so I waited till the bugs were beaten out of that unit before that part was shipped as I knew I didn't want the old egg timer.  I just got up and running in Sept of 2014  System is a mix of PEX tube in concrete, Warmboard, a few radiators,  DHW - all scattered between a couple buildings and a backup Triangle Tube LP boiler to keep things going if I'm not here to feed the beast.  It it got pretty complicated pretty fast so I had Karl put together a design with the hope of finding a local to wrench the big parts together. Karl ended up with a hole in his schedule for a few days and ended up coming up and using me as his gopher.  Overall a great solution and a great guy to work with. I keep wanting to document the thing and throw it out on the web site, but always run out of time.

Keep us posted.

Dan


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## TCaldwell (Feb 16, 2015)

The 3/4 ports would be handy for the filter loop but I'm afraid too small for the mix loop. That unavailable hot water at the top does mix and actually helps maintain the supply temp at the beginning of the burn/mix. I have a tekmar sensor on the boiler right next to the supply bung, when the mix starts the supply temp maintains while the tank temp equalizes, as the burn progresses the the supply temp increases. The unavailable water acts as a buffer.


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## gregwhs2000 (Feb 17, 2015)

OK, so probably a dumb question here ... but I will ask it anyway.  What if you just dropped one of these in the tank through the manway .... with an appropriate length discharge pipe that's secured somehow to the overflow pipe or some other means?  Then you just need a very small slot machined to allow the power cord to pass under the manway cover and you are in business.

http://www.supplyhouse.com/HT41M-4-10-HP-High-Temperature-Submersible-Sump-Pump-115v-10-ft-Cord-200F

Would such a pump be durable enough when used like this?  I realize this eliminates the ability to filter, but that could be done numerous other ways.  Pumping would be from bottom to top, but with such a high GPM I would think it would mix the tank in minutes.


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## TCaldwell (Feb 17, 2015)

I'd think that would work as you suggest, it would cost all that to externally plumb and pump it


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## varadhammo (Feb 17, 2015)

gregwhs2000 said:


> OK, so probably a dumb question here ... but I will ask it anyway.  What if you just dropped one of these in the tank through the manway .... with an appropriate length discharge pipe that's secured somehow to the overflow pipe or some other means?  Then you just need a very small slot machined to allow the power cord to pass under the manway cover and you are in business.
> 
> http://www.supplyhouse.com/HT41M-4-10-HP-High-Temperature-Submersible-Sump-Pump-115v-10-ft-Cord-200F
> 
> Would such a pump be durable enough when used like this?  I realize this eliminates the ability to filter, but that could be done numerous other ways.  Pumping would be from bottom to top, but with such a high GPM I would think it would mix the tank in minutes.



I like it. Only observation is that it will use a fair bit more electricity than a wet rotor or ECM circ. But since you're only running it when charging, probably not a big deal.


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## gregwhs2000 (Feb 17, 2015)

varadhammo said:


> But since you're only running it when charging, probably not a big deal.



If I go this route, what I would really like to do is control the pumps power by using the controller outlet and also adding a timer control that just runs the pump for x minutes, every y minutes ... where x and y could be configured.  I doubt a pump with that GPM needs to run the whole firing time to keep things mixed.


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## heaterman (Feb 18, 2015)

gregwhs2000 said:


> OK, so probably a dumb question here ... but I will ask it anyway.  What if you just dropped one of these in the tank through the manway .... with an appropriate length discharge pipe that's secured somehow to the overflow pipe or some other means?  Then you just need a very small slot machined to allow the power cord to pass under the manway cover and you are in business.
> 
> http://www.supplyhouse.com/HT41M-4-10-HP-High-Temperature-Submersible-Sump-Pump-115v-10-ft-Cord-200F
> 
> Would such a pump be durable enough when used like this?  I realize this eliminates the ability to filter, but that could be done numerous other ways.  Pumping would be from bottom to top, but with such a high GPM I would think it would mix the tank in minutes.




I like it.
Less cost than a mix loop and about zero labor involved.

I'd probably set it up with a riser pipe about 2-4" below the nominal water level of the tank and put a tee on the top to direct the water to the front and the back of the tank. Run it through a timer that cycles on for 4-5 minutes every hour or two. Specs on that pump show it would run in the range of 50-55GPM in that situation.


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## Karl_northwind (Feb 18, 2015)

But you'd only want to run it while firing, to be sure. 
I wonder if they make smaller ones.  I've looked for such things, and not found them.  time to look again.
You could definitely filter.  High temperature bag filters can be found pretty easily, and as long as you can let the temp get low enough to reach in and change it, you'd be OK. 

k


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## gregwhs2000 (Feb 18, 2015)

Karl_northwind said:


> But you'd only want to run it while firing, to be sure.
> I wonder if they make smaller ones.  I've looked for such things, and not found them.  time to look again.
> You could definitely filter.  High temperature bag filters can be found pretty easily



Being the novice that I am, I was not aware you'd be able to filter inside the tank.  I did some googling but nothing so far.  If you have a link handy, please post it.  Would be nice to get a filtering solution at the same time.  May be a no-brainer for me at that point.


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## Karl_northwind (Feb 18, 2015)

gregwhs2000 said:


> Being the novice that I am, I was not aware you'd be able to filter inside the tank.  I did some googling but nothing so far.  If you have a link handy, please post it.  Would be nice to get a filtering solution at the same time.  May be a no-brainer for me at that point.



http://www.mcmaster.com/#standard-filter-bags/=vyo26j

My go-to source for all sorts of oddball stuff.  some ABS or steel fittings (temperature ratings) and you should be good for a while with those bags.


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## gregwhs2000 (Feb 18, 2015)

Thanks Karl.  Lots to chose from ... what material and micron size would be best?  Would the polypropylene pipe adapter models be better than just tying the bag on?

FYI ... the link to the Liberty pump was the smallest high temp model that I could find.  I agree something smaller that just ran continuously on the controller outlet during firing would be simpler, but I've not found such a beast.


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## Karl_northwind (Feb 18, 2015)

sorry, the link didn't  go where I thought it did. 
try this one.  75 micron, 50 GPM.  it's an 11" opening, so some sort of fitting is in order. 

http://www.mcmaster.com/#2514k49/=vyoim9
karl


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## eauzonedan (Feb 18, 2015)

Gotta love this brain trust once the ideas start rolling in. Dumb question: there is already an outlet (high) and inlet (low) on the back wall of the round Garns. Would the addition of even a 3/4 outlet (low) and 3/4 inlet (high) on the front face of the tank  maybe start a circular movement within the tank to facilitate better mixing than just the 3/4 pipe would suggest?  This would be there for up to the full burn duration of a couple hours. Just brain farting here...


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## varadhammo (Feb 18, 2015)

Karl_northwind said:


> some ABS or steel fittings (temperature ratings) and you should be good for a while with those bags.



Could you use ABS pipe for the pump riser inside the Garn? I looked up the numbers and ABS has a glass transition point of 221°F and pressure rated up 180°F. So it seems to me it should be alright...? It would be an easy way to go, could do the pump riser, tee, and even a horizontal diffuser (pipe with holes drilled) out of 1-1/2" ABS pipe. Diffusion may be immaterial at 50gpm, though 

Also, I looked at those Liberty pump models and you could go with the HT450 (http://www.supplyhouse.com/HT450-1-...erature-Submersible-Sump-Pump-115v-10-ft-Cord) and save a few more bucks...that's the cheapest model they have and it is auto not manual, but has a piggyback plug which can bypass the float switch.


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## gregwhs2000 (Feb 18, 2015)

I looked at that pump as well, but decided the few bucks extra might be well spent in buying the heavier cast iron version.  I'm thinking black iron piping may be better too, since more weight may be better ... you won't want to flip the power on and have this baby going on a cruise of the inside of your tank!  

Maybe I'm overestimating it, but it seems like a good idea to keep it heavy if you can so that the lateral flow does not cause it to move around too much.


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## varadhammo (Feb 18, 2015)

gregwhs2000 said:


> I looked at that pump as well, but decided the few bucks extra might be well spent in buying the heavier cast iron version.  I'm thinking black iron piping may be better too, since more weight may be better ... you won't want to flip the power on and have this baby going on a cruise of the inside of your tank!
> 
> Maybe I'm overestimating it, but it seems like a good idea to keep it heavy if you can so that the lateral flow does not cause it to move around too much.



Yes, good point.

Did you find anything for a cycle timer yet?

I'm getting ready to modify my setup as well, and I'm thinking about going the same route as you... With my current setup, the way we've been doing it is manually flipping valves and switches to go between "mix mode" and "stratify mode". I'm going to change over the primary/secondary plumbing behind the Garn to simple supply & return headers with no primary pump, and add a mixing pump separately.


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## gregwhs2000 (Feb 18, 2015)

varadhammo said:


> Did you find anything for a cycle timer yet?



Not yet.  I found some countdown timers, but not really what I'm looking for.  

I did just order the pump, but not sure how quick it will get here.  I may just run it manually for a bit and then sort it out.  On the flip side, I have been thinking about this device which would be used for doing much more than just controlling the mix pump:

http://www.controlbyweb.com/x300/

Overkill to just control the mixing, but I've got some other uses for it and it would be great to check the Garn temps without walking out there.


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## ewdudley (Feb 18, 2015)

I've had good luck with SESTOS timers similar to this one:

http://www.ebay.com/itm/100-240V-AC...971?pt=LH_DefaultDomain_0&hash=item3cc5dbd7eb

Contacts are only rated for 3 amperes resistive, so probably should use as a pilot relay for a motor relay/contactor.


----------



## TCaldwell (Feb 18, 2015)

With 2000 gal at 50 gpm that's 40 minutes for a turnover. Not sure how much on/off during a burn you will need. If the x 300 does differential measurement, one sensor at the bottom and one on the top, when the differential is less than 5 deg the pump is off and on when over during a burn, just a thought.


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## TCaldwell (Feb 18, 2015)

If you are triggering off the inducer through the garn controller that has sensitive temp wiring, might try a solid state relay for isolation.


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## varadhammo (Feb 18, 2015)

I was just realizing that having that pump and the blower fan both plugged into the duplex GFCI on the controller will probably overload the circuit, especially on startup when they both power on simultaneously. The Liberty sump pump draws 12A full load, the 3/4 hp blower fan is ~13.8A. The relay in the Garn controller box may be rated for 30A, will have to check. I only have 12ga romex running to mine though, wouldn't be enough to run 30A. The relay in the Garn controller box is DPDT but only one pole is used for that GFCI, so you could use the other pole to trigger the timer relay that Tom suggested...


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## gregwhs2000 (Feb 18, 2015)

TCaldwell said:


> With 2000 gal at 50 gpm that's 40 minutes for a turnover. Not sure how much on/off during a burn you will need. If the x 300 does differential measurement, one sensor at the bottom and one on the top, when the differential is less than 5 deg the pump is off and on when over during a burn, just a thought.


The X300 could be programmed to look at the differential of two sensors so that would certainly be an option.


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## heaterman (Feb 18, 2015)

Karl_northwind said:


> But you'd only want to run it while firing, to be sure.
> I wonder if they make smaller ones.  I've looked for such things, and not found them.  time to look again.
> You could definitely filter.  High temperature bag filters can be found pretty easily, and as long as you can let the temp get low enough to reach in and change it, you'd be OK.
> 
> k




Karl I'm going to jump in here and offer my $.02 worth regarding when to run it.  And maybe this will affect how some of this gets implemented.

I have not seen any issues at all, in any size Garn concerning stratification while firing. The hottest HX tubes are located at the bottom of the tank and from what I have observed/measured, any stratification existing in the Garn is pretty much gone within 15 minutes of starting a fire. The tank temp measured on the LWCO stem will in many cases drop after a burn gets going due to the mixing occurring in the tank when those bottom tubes get rocking.
If you take the man hole cover off you can actually see the water moving up from the bottom of the tank.
Personally I don't think stratification DURING firing is an issue.


The stratification problem I see (in some installations) is not so much top to bottom but front to back.
Under low flow conditions, which I will arbitrarily call out as under 10GPM, the front of the tank above the fire box seems to "stack" for lack of a better term. It just sits there and doesn't move. This robs the system of available btu's that are basically held in storage but not available for use.
Addressing that issue with something like the high temp sump pump mentioned above "stirring" the tank intermittently would keep those btu's in circulation.

I don't think a constant mix is a good solution as you want to maintain some stratification top to bottom in order to keep highest available water temp at the supply outlet on the tank.


----------



## Buzz Saw (Feb 18, 2015)

gregwhs2000 said:


> Not yet.  I found some countdown timers, but not really what I'm looking for.
> 
> I did just order the pump, but not sure how quick it will get here.  I may just run it manually for a bit and then sort it out.  On the flip side, I have been thinking about this device which would be used for doing much more than just controlling the mix pump:
> 
> ...


Here is a much cheaper option.
http://www.automationdirect.com/adc...kable_Micro_Brick)#sort=item_code+asc&start=0
(Or which ever variant you choose)
You would need to also buy a power supply. I'm pretty sure the software for programming is still free. I suspect the internal relays can't handle the amps of the pump so external relays would be required. Guessing, I would say you could do this for around $125 and control the pump to your hearts content.  You could also incorporate water temp sensors to signal pump on and off.

Take a minute and check out that site. If you want to automate something they probalby have it, and have it cheap.


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## gregwhs2000 (Feb 18, 2015)

heaterman said:


> Personally I don't think stratification DURING firing is an issue.



I guess I would have to disagree in that the stratification will eventually mean you have to stop firing because the top layer of the tanks water has reached the maximum temp recommended.  If you are able to mix that max temp water with cooler water from lower in the tank, then firing can continue.  Unless you mean there is no stratification during all firing after the turnover, which I would really find hard to swallow.  Perhaps turnover eliminates stratification for a short time while firing, but it can't be for long and by the time firing ends due to max temp at LWCO there's certainly plenty of stratification in my tank.

My supply temps never come within even 10F of the tank temp reading from the LWCO during firing, usually about 20-25F difference.  So at the very least starting the post-fire cycle with supply temps nearly matching the LWCO reading would be a big improvement in total BTU's stored.  Since I believe that even bigger drops in temp are found below the supply inlet, mixing should provide a big improvement in total BTU's stored.

Regardless of theories, we're about to find out.  I'll post my observations once the pump is put to use for a few cycles.


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## varadhammo (Feb 19, 2015)

heaterman said:


> I have not seen any issues at all, in any size Garn concerning stratification while firing. The hottest HX tubes are located at the bottom of the tank and from what I have observed/measured, any stratification existing in the Garn is pretty much gone within 15 minutes of starting a fire. The tank temp measured on the LWCO stem will in many cases drop after a burn gets going due to the mixing occurring in the tank when those bottom tubes get rocking.
> If you take the man hole cover off you can actually see the water moving up from the bottom of the tank.
> Personally I don't think stratification DURING firing is an issue.



Yeah, from experience I'd have to disagree as well. I am intrigued by the difference in what @heaterman has observed and what I'm seeing in my own unit. What I've observed (see datalogger graphs above in this thread, https://www.hearth.com/talk/threads/garn-stratification-vs-homogenization.141118/#post-1901377), seems quite the contrary to what he describes. I wonder what gives! In the first graph I posted above, I fired the Garn without the mixing pump running and the top was boiling at 208F while the bottom was 90F, middle was ~140F... With the pump on I can get the top to 190F, bottom to 180F.


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## jebatty (Feb 19, 2015)

This is not quite the homeowner situation. With the Garn 3200 at Deep Portage, and a 69 gpm circulator, which basically runs all the time when the heating system is active, the 3200 gallons are always mixed. When the Garn is used, it is usually fired to maintain 140-160F water supply to the system. It's 3200 gallons also doubles as shared system storage, along with 4000 gallons external storage which primarily serves a Wood Gun E500. The unpressurized Garn is isolated from the system and supplies the system via a large plate HX. 

Deep Portage uses fan coil units for space heating, it has no use for low temperature supply water, so a mixed tank at 140-160F provides maximum btu's to the system.


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## Karl_northwind (Feb 19, 2015)

heaterman said:


> Karl I'm going to jump in here and offer my $.02 worth regarding when to run it.  And maybe this will affect how some of this gets implemented.
> 
> I have not seen any issues at all, in any size Garn concerning stratification while firing. The hottest HX tubes are located at the bottom of the tank and from what I have observed/measured, any stratification existing in the Garn is pretty much gone within 15 minutes of starting a fire. The tank temp measured on the LWCO stem will in many cases drop after a burn gets going due to the mixing occurring in the tank when those bottom tubes get rocking.
> If you take the man hole cover off you can actually see the water moving up from the bottom of the tank.
> ...


 
My recommendation to only mix when firing was mostly just so you don't mix the tank too much (50 GPM) during heat storage periods.  and somewhat for energy consumption reasons.  and 50 GPM is plenty to mix/filter even a 2000 several times during a several hour burn. 
the GARNs I've installed all have the cold return piped at least halfway to the front of the unit.  I would think this would help the front to back stratification.


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## heaterman (Feb 19, 2015)

Backing up a step or two here regarding stratification. Let's talk about when you want it and when you don't.
These are the operating characteristics I like to see when setting a system up.

When you are charging heat into your storage, regardless of what type of storage you have, you want total mixing of the entire volume. This will allow maximum btu's to be held in your "battery". In any type, shape or size of vessel, this would mean same temp top to bottom and side to side.

When pulling heat from storage you would ideally like to have a situation where you are pulling the highest temperature water in the vessel (always at or near the top) out to your loads and returning the coldest possible fluid back to the bottom. The greater temperature difference you can create, the better it will stratify all other things being equal.
This format will provide maximum drawdown of the heat before having to refill.

Is there agreement on those points? Or am I missing something?

Now speaking specifically to some points brought up about the Garn tank vs supply temp sensors........I have found that the actual water temperature is closer than what they read. The main factor in play there is that the tank is an immersion sensor in direct contact with the fluid and the tank sensor is a surface mount/contact type sensor. The supply sensor is always going to be lower than the tank sensor reading. I'm at the point where I automatically assume the supply is 10* warmer than the reading shows. That has been my observation in the field when I measure the temps with my own meter.  (Fluke 116 with thermocouple)

What I have observed with some Garn installs, specifically with the 2000, is that after the tank has been drawn down for a while, I can just about draw a diagonal line starting about midway up the loading door and ending at the back of the manhole, which will have noticeably warmer water in it than the rest of the tank. Sometimes as much as 25*.
It seems that hot water will stack in that area and somehow due to currents or flow in the tank, not find its way back to the supply opening on the unit. Some of this might be due to the residual heat in the fire box or maybe just the fact that the firebox itself impedes internal circulation. I don't know and have never heard a good explanation of why it might be so either.  To me this particular phenomena is not an ultra critical issue because the volume is relatively low in comparison to the total capacity. 

Bear in mind that every Garn we have ever installed has been constant circulation in the tank itself.

Gotta run.


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## gregwhs2000 (Feb 19, 2015)

heaterman said:


> Is there agreement on those points? Or am I missing something?



All in agreement here.  I've tried to be precise in stating pretty much the same things you've said ... but that can't happen in every post and so that can lead to uncertainty for sure.



heaterman said:


> about the Garn tank vs supply temp sensors........I have found that the actual water temperature is closer than what they read



My supply numbers are from analog thermometers in immersion wells in copper pipe located just before an exchanger.  I suspect they are fairly accurate although I would give even more credence to  varadhammo's numbers.  To me it's extremely clear that there's opportunity to get more homogenization during firing, outside of the rollover effect.

I did want to say that nothing on this stratification topic is seen by me as a major flaw in the Garn design.  It's a simple machine and I think sometimes there is push-back against ideas that make it less simple.  I can understand that, but reserve the right to add complexity to my Garn when I feel its worth the effort.  The Garn rocks IMO ... no matter how much I elect to tinker with it.


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## varadhammo (Feb 19, 2015)

heaterman said:


> Now speaking specifically to some points brought up about the Garn tank vs supply temp sensors........I have found that the actual water temperature is closer than what they read. The main factor in play there is that the tank is an immersion sensor in direct contact with the fluid and the tank sensor is a surface mount/contact type sensor.


Agreed, in my case I have the "supply" and "return" sensors taped to back face of the Garn at about halfway down the tank and at the level of the return bung, respectively. They are useful to be able to read at the controller, but compared to the readings from my string of immersion sensors (see above) they can be about 10 degrees lower. So I don't give much credence to the surface readings except as a rough (and useful) guide.

I have just found somewhat conclusively (with my setup at least) that without a mixing pump, the top of the tank can reach maximum temperature while the middle and bottom are not yet up to temperature, which significantly limits the amount I can "charge the battery". With the pump on, I can get a more or less full charge top to bottom. Without the pump, I can't. Like I said above, I know this is at variance with what @heaterman and perhaps others have found (i.e. that the heat from the firebox & hx tubes causes the Garn to mix itself to a significant extent while firing), and I do wonder why... anyway, I second Greg's sentiment in appreciation of the elegant simplicity of the design...and also in reserving the right to keep tinkering


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## TCaldwell (Feb 19, 2015)

Tinkering and the ingenuity of the forum  community with respects to the garn is unprecedented. Rightly so their reluctance to change has kept the product true. However today's market no mater what the product demands optimization.


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## heaterman (Feb 19, 2015)

varadhammo said:


> Agreed, in my case I have the "supply" and "return" sensors taped to back face of the Garn at about halfway down the tank and at the level of the return bung, respectively. They are useful to be able to read at the controller, but compared to the readings from my string of immersion sensors (see above) they can be about 10 degrees lower. So I don't give much credence to the surface readings except as a rough (and useful) guide.
> 
> I have just found somewhat conclusively (with my setup at least) that without a mixing pump, the top of the tank can reach maximum temperature while the middle and bottom are not yet up to temperature, which significantly limits the amount I can "charge the battery". With the pump on, I can get a more or less full charge top to bottom. Without the pump, I can't. Like I said above, I know this is at variance with what @heaterman and perhaps others have found (i.e. that the heat from the firebox & hx tubes causes the Garn to mix itself to a significant extent while firing), and I do wonder why... anyway, I second Greg's sentiment in appreciation of the elegant simplicity of the design...and also in reserving the right to keep tinkering



First of all do not interpret anything I say as a warning against tinkering. Tweaking, fiddling with or just messing around with one's stuff, especially mechanical stuff is the American way!   

I'm wondering if some of the difference in the tank blending depends on the temperature at which you stoke thing up again?  
Thinking back to what particular installation I observed the rapid convective mixing taking place I recall that specific instance as being re-fired with the return sending water back to the unit at about 90* and the tank thermometer (analog at that time and located about 12" down from the top, on the face) as being in the 120* range.
It could be that rapid mixing of the tank is more pronounced when there is a larger T going on in the tank rather than if one began charging at say 140 or 150*.


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## ewdudley (Feb 19, 2015)

ewdudley said:


> I've had good luck with SESTOS timers similar to this one:
> 
> http://www.ebay.com/itm/100-240V-AC...971?pt=LH_DefaultDomain_0&hash=item3cc5dbd7eb
> 
> Contacts are only rated for 3 amperes resistive, so probably should use as a pilot relay for a motor relay/contactor.



But why not control to a setpoint?  

PID controller in cooling mode with [for example] a three minute PWM bang-bang cycle.  PID controller would automatically adjust on-off timing to maintain temperature at top of tank to setpoint.

http://www.ebay.com/itm/AC-110-240v...818?pt=LH_DefaultDomain_0&hash=item5d4d9155b2


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## varadhammo (Feb 19, 2015)

heaterman said:


> It could be that rapid mixing of the tank is more pronounced when there is a larger T going on in the tank rather than if one began charging at say 140 or 150*.


That could very likely be the case. I'll have to do that experiment some time. It makes sense that a larger delta T between the HX tubes and the surrounding water, will create more convective mixing.



ewdudley said:


> PID controller would automatically adjust on-off timing to maintain temperature at top of tank to setpoint.


I don't get it...how does this provide tank mixing?


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## jebatty (Feb 20, 2015)

Is this discussion, and especially Heaterman's "Is there agreement on these points?", intended to be limited to the Garn or does it include other gasification boilers with an external storage tank? The agreement may be different depending on the scope of this discussion.


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## ewdudley (Feb 20, 2015)

ewdudley said:


> But why not control to a setpoint?
> 
> PID controller in cooling mode with [for example] a three minute PWM bang-bang cycle.  PID controller would automatically adjust on-off timing to maintain temperature at top of tank to setpoint.





varadhammo said:


> I don't get it...how does this provide tank mixing?


If the mixing pump was over-sized like the one above, the PID controller could adjust the duty cycle to maintain the temperature at the top of the tank more or less at a constant setpoint temperature.  In cases where there is no pressing need for hot water during the burn then no need for temperature control.


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## eauzonedan (Feb 20, 2015)

Some real world numbers on the last 11 burns in my 1500  Note that my Garn side HX pumping rates bounce all over the map as my different emitters can call for supplying either 140 or 115 degree water and depending what's calling and the number of them  - the variable speed pump on the Garn side of the HX ramps up and down to hit that selected set point on whatever flow is on the building side  of the HX .  At this point I have no good way to correlate that variable pumping rate as it relates to any stratification numbers. These averages are generated from three wet thermometers in the tank located at the mid point as well as near the top and bottom - all below the manhole opening.  One odd thing I see is that I get up to a 10 degree difference between my top thermometer read and the Garn controller value at the end of a  draw down, but they are spot on after a recharge.  My thought is that there is a extremely sharp temperature change per elevation change at the end of a draw down and even an inch of elevation of the thermometer can skew the numbers pretty well.

Here are the average temperature difference between the top sensor and either the mid or bottom one averaged over my last 11 burns

Top to mid of tank before a burn 33.5 degrees
Top to bottom of tank before a burn 39 degrees

Top to mid of tank after a burn  7 degrees
Top to bottom of tank after a burn 33 degrees

It looks like Steve is pretty spot on (imagine that!) about the mixing that goes on during a burn and that the post burn stratification is not as bad as I originally thought.  The bulk of the volume is at the mid point of the tank - so the bottom sensor represents a much smaller volume of water, and thus btu's and % or storage volume.   It still would be nice to homogenize and stretch out the burn a bit more........... that 7 degrees looks to be maybe another 10-15% of effective storage in my case.

Anybody kick around the idea of an internal bubbler?  Works great to keep docks from freezing up.  Might need to draw the air from inside the boiler and then return it to keep from inducing "fresh air" that could lead to come corrosion issue?  more brain flatulence......l


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## gregwhs2000 (Feb 20, 2015)

eauzonedan said:


> Top to mid of tank after a burn  7 degrees
> Top to bottom of tank after a burn 33 degrees
> 
> so the bottom sensor represents a much smaller volume of water, and thus btu's and % or storage volume.   It still would be nice to homogenize and stretch out the burn a bit more........... that 7 degrees looks to be maybe another 10-15% of effective storage in my case.



Your numbers confirm the turnover effect, but I think you may have understated the potential for more BTU's in the same water.  I think that the bottom represents as much or more of an opportunity as the middle ... because even with less volume, the bottom temp differential is 4+ times greater than the middle. 

I stop burning when the LWCO reaches 185-190F ... but once I start mixing, I plan to stop burning at 180F ... and even with the lower max temp, I expect a significant improvement in "battery life" once nearly all the water is able to reach maximum temp.  Time will tell.


----------



## TCaldwell (Feb 27, 2015)

Did the high temp sump pump come in yet?


----------



## jebatty (Feb 27, 2015)

Just for the fun of it, three days ago I fired the Tarm, turned off all draws on the system/storage, turned on a circ that draws from top of tank and returns to the bottom at about the middle of the tank, and with a weighed wood burn brought storage top up to 201F (12" down from the top), middle 201F, and bottom 195F. Horizontal 1000 gal tank. The Tarm hi-limit sensor at very high temp supply reads about 8-10F less than the actual hot water output, so I was able to do this without causing the Tarm to idle. All sensors are DS18B20 fixed to the tank surface under all of the tank insulation.

The horizontal tank would mimic a Garn tank.


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## gregwhs2000 (Feb 27, 2015)

TCaldwell said:


> Did the high temp sump pump come in yet?



I've got everything ready to go ... but still waiting for the pump to ship.  Hopefully next week.


----------



## R. Snyder (Mar 6, 2015)

gregwhs2000 said:


> I've got everything ready to go ... but still waiting for the pump to ship.  Hopefully next week.


Hi,
Just wondered about the progress on this project.


----------



## heaterman (Mar 6, 2015)

R. Snyder said:


> Hi,
> Just wondered about the progress on this project.



I heard from Greg this morning and he was hoping to get some results in the next week or so.


----------



## gregwhs2000 (Mar 6, 2015)

heaterman said:


> I heard from Greg this morning and he was hoping to get some results in the next week or so.



Yes the pump was delayed but is in route so hopefully next week I'll have some results.  Here is my simplified plan for manually measuring the potential benefits of mixing:

Burn as normal and get to a max temp of 185-190 and record the LWCO temp
After the burn is over, run the pump for 15 minutes and record the new LWCO temp
Weigh some dry hardwood and then start a new burn with a target 180 LWCO temp
As 180 approaches, run the pump another 15 minutes while the burn is in progress and measure LWCO temp
Add more weighed wood if needed and repeat mixing and adding wood as many times as practical
When the fire is out, record final LWCO temp (and burn time just for kicks)
Calculate additional BTU's added by the additional burning that was enabled by the mixing capability
I will calculate the additional BTU total by estimating based on the weight of the wood burned and also with the total additional degrees of heat added to the water.  I'll have to assume that the tank temp is homogeneous at the end of the first and last mix in order to calculate the later.  Maybe that's not a perfect calculation if it's not 100% mixed, but with the other calculation based on wood weight, it should give some decent data points and if they are close to the same, then both are probably good measures.

I'll also make sure the external pump is off during the measurements.  Once I have some results, I'll post them in this thread and then decide how to best automate the mixing for next winter.


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## Boil&Toil (Mar 8, 2015)

Might be able to adapt a milk bulk tank mixing paddle/propellor as a "destratifier" (but no filter) - designed for pretty much the same job in pretty similar tanks, going the opposite direction (cooling the warm milk.) Would only be practical if you found one going for junk price, though.

For controller logic I'd probably look at "is blower running" and "is top within 5 degrees of cutoff?" (or 10, or whatever floats your boat) and punch a 3 minute minimum run relay. After 3 minutes it would either stop until the top got hot again, or keep going if it was still hot. 

For the external loop/filter version, I have a combination SS mesh/vortex filter on my well - those are also made in hot water versions. Good idea to box it though - inspection is nice (clear filter case), but algae can be surprisingly adaptable, so not lighting any part of the system is a good precaution IMHO. Plus the box would help limit the circulating loop from blowing heat to the boiler shed.


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## gregwhs2000 (Mar 11, 2015)

Pump arrived and I have it in the tank, but am not happy with it yet.  The exchanger tubes prevent the pump from resting straight down vertically, so the discharge "T" is at an angle instead of being level with the water.  I'm going to get four street 45's and loop the discharge downward, then mount the pump on a chain just below the water level so that I am pumping top to bottom.  The discharge "T" will slide right between two of the exchanger pipes. Hopefully I'll get time for that over the weekend.  I've really thought all along that pumping down is better anyway.

I did run the pump once last night just for kicks.  I had a burn almost to the end at the time and the LWCO temp was 183 when I turned the pump on.  After 20 minutes, it was 177, and that's with one of the discharge outlets angling downward, so I think this pump will get a good mix going in a short amount of time.  That should allow for a full charge of the "battery".


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## Buzz Saw (Aug 21, 2015)

Greg, did you make anymore burns with your mixing pump before the season ended? 

How were the results if you did?


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