Garn Stratification

[bpirger]

Has anyone measured the stratification in their Garn?

My sensor in the thermowell was telling me 144. If I positioned my thermistor about 10" over the well on the front face of the Garn I measured about 175. At the well, I measured 144. I was amazed that they agreed. About 30" below the well I measured about 123.

Water coming out of the Garn had my 2" pipe at about 128 or so. Circs were constantly running here. Last firing was about 10 hours previous to this.

The water outlet is about the same height as the well, I'll have to check the exact difference. But, the outlet feed certainly isn't at the very top of the unit, there's at least 10" of water over the top of the outlet....

I assume I'd just getting the water at the outlet level. Since the Garn doesn't take water off the true top of the unit, I'm not sure there's anything I can do about this.

Any other observations or comments?

I then started another fire. Interestingly, the water out the 2" feed line was up to about 149 yet the thermowell was staying at about 145 (It had dropped down to 139 in the meanwhile before I started the fire). I'm assuming that the turbulence in the tank is performing some mixing of the water as well as the fire introducing heat.

I'm finding that I can heat the house just lovely with the Garn, as my radiant is pleased as punch with just 120 degree water tops. That's the limit I have going into the floor at the moment. But, it is a hassle to heat the DHW as the Garn water at 120 will do it rather slowly. I dropped the DHW sensor down to 115, so it will shut off the DHW pump when the tank reaches 119. Still plenty of heat left for the floor, but its tough to do the DHW down at this level. Considering the idea of changing the DHW control to another unit and actually burning oil a bit just to fire the DHW if the boiler supply is less than say 130.

Thanks!

 

[Rick Stanley]

Here's a thread from last year where we talked about this quite a bit.

https://www.hearth.com/econtent/index.php/forums/viewthread/34365/

If that won't work, just search on "Garn difference front and back"

Rick

 

[bigburner]

Here's stratification, I was filling the planet killer yesterday and decided to start a fire. it takes a couple hours to fill and a while to get the fire hot. Any way i was putting in 50 F water in the bottom an had it making steam on the top. you cold feel the boundary layer with your hand on the side of the boiler. It's 7 ft tall so there is some room for vertical stratification. It was kind of interesting that when it was full how long that very hot temp lasted, my boiler has mud legs and heats from the bottom & the fire tubes so I think I can get away with out trying to mix. Thinking by lowering the GPM I might be able to take better advantage of the Delta -T top to bottom. I am piped to a 200 Gallon hydraulic separator so that should help any in-balance. My guess for the Garn issue is that there is a dead spot above the combustion chamber that allows a pocket of hot water to hide without effective mixing, some one on here must have or know of a fluid dynamics program, think it would be pretty simple to load in the parameters.

 

[TCaldwell]

Congratulations on your setup, being able to productively use lower supply temps is the key the effiency of storage. Understanding the crux of needing domestic supply of 125+degf kind of defeats the idea. One way to accomplish this would be to supply your indirect hw tank with the garn 120 deg or even less then plumb the supply into a elec hwh set at 125-130 deg to bring it up to desired temp. The low delta t between the temps will not use much electricity.

 

[bigburner]

making DHW isn't a problem, making a lot of it is!! a very hot shower is 119 F add in a heat exchange or two and the supply has to be about 140F and with that low Delta -T it just exasperates the problem. On those Garns you could just open it up and take a bath LOL

 

[bpirger]

Thanks guys (Randy), that is exactly the thread I needed...and exactly the "problem" I see. It does seem like I might be better off thinking of a way to supplement the hot water creation....or just burn more often. I'm at once every 24 hours....so that isn't bad. And I have yet to button up the front of the Garn and currently still dumping some heat in the ground. Once that is fixed (as soon as I can tie in the new buried lines), I will likely be good to go. I'll certainly do that before anything else.

I'll chew on that past thread...but I'm sure I'm seeing exactly the same thing....

Thanks! Bruce

 

[heaterman]

Bruce

Sounds like you are on the right track with the priorities on your project list. As to the DHW production, there is no way to get around the fact that you need fairly high water temps to make good use of an indirect. The only options you have are to maintain 140+ in the Garn or use it to get whatever you can and then boost with something else like Tom has suggested. I usually just place an aquastat on the line from the Garn to the indirect that kills flow if the Garn is below 140 and let a different device take over. At temps above that the aquastat turns on the circ or opens a zone valve, depending on how I have the system configured and the Garn takes over.

Regarding stratification in a Garn, yes, they stratify very nicely and there is some variation front to back depending on flow rate going back into the unit. The amazing thing to me is the reverse stratification or blending that occurs when you light a fire in it. I have watched the front thermometer actually drop 10* within just a few minutes of firing due to tank turnover. The heat transfer once you put a fire in the thing will turn over the entire 2000 gallons about every 5 minutes from what I have observed bringing the coldest water from bottom to top. If you lift the lid and watch, the water is moving with enough velocity that you can actually see the flip. (Don't fall in and don't lift the lid on a hot tank unless you want a steam bath)

 

[jebatty]

Heaterman: The heat transfer once you put a fire in the thing will turn over the entire 2000 gallons about every 5 minutes from what I have observed bringing the coldest water from bottom to top.

Isn't this "not" stratification? Garn advised that when the Garn pump is running during a firing or between firings, there is very little stratification due to the mixing you describe. This supports the very good low temperature radiant application for a Garn.

 

[bpirger]

Jim: There is no stratification during the burn......but after the burn is complete it is quite clear there is stratification that develops. What clearly happens though is that eventually, maybe 10 hours, maybe 12, depending on load....the Garn output lies below the hot water layer..so the water coming out of the Garn can be considerably cooler than the water aroound the thermowell sensor. So, the front thermowell sensor may say 145, but the water exiting the 2" supply at the rear of the Garn is about 125. I've seen this exact thing happen.....and above the thermowell it may actually be up to 150-160... Huge stratification develops....and apparently from front to rear of the Garn as well...not just vertically...which is peculiar for sure!


Yeah, I've grown convinced I have to do something different for DHW. My DHW pump will come on and run for a long time, usually eventually taking the heat out of the DHW and back into the primary loop!

First switch over to the microflex, then see what happens....though it will be the same issue but just take longer.....then use a sensor I think to fire the oil boiler when the DHW pump is running and the DHW suupply is below 140 or so. Or just burn more wood.....

The reality of heating with cool water radiant from storage....completely expected as well.

 

[RowCropRenegade]

I have seen the same stratification on my Garn.

The front temp gauge is generally pretty accurate about 1.5 hour into the burn. By then that top layer is mixed with the cooler lower level and the gauge will drop then start rising. The further away from the end burn time I get, the more I've relied on my temperature coming inside when deciding to fire. The flue temp gauge also has been a handy indicator of when to fire. I've seen the front gauge read 185 and only be getting 150 degree into the house. My top sensor on the outer portion of the tank towards the top verifies what you are seeing. I don't see much variation from front to back. But it shows those 100 gals of unusable heat. No biggie, I'd rather have those trapped btus than have to worry about sucking air.

It has been in the lower 20s and teens the past couple days. Wind blowing pretty good. Running the unit about 7 hours a day. Big difference in setting the tstat to 68 than 72. I'm pleased at it's ability to convert wood to energy. I wish I had radiant instead of baseboard. Ive consistantly been running it up to 200-205 to get me 10-12 hours of standby. House needs more insulation and more baseboard fins.

 

[Rick Stanley]

Ok, so the gauges seem funky on a Garn system because of a hot layer of water that we can't get and the mixing that occurs when we build a fire in it. Got it. Still seems weird, but I got it.

To take full advantage of the huge on-board storage of a Garn, you need radiation that can perform with low temp water. Got it. Got it literally. I have lots of cast iron rads and some radiant floor. Have been able to stay comfortable in a drafty old farmhouse with daytime temps barely above freezing with water as low as 110* especially if the sun comes out at all. Cool!

Especially cool if you want a shower toward the end of the burn cycle. You can't make 125* shower water with 110* boiler water. Got it.
So I'm looking at boosters. Something to bring 100* DHW the rest of the way up to 125*. Might this be a good option? Anybody know anything about these units?

http://www.pexsupply.com/Eemax-EX280T2T-EX280T2T-Whole-House-Electric-Tankless-Water-Heater

Rick

 

[Sawyer]

I have seen the same stratification on my Garn.

The front temp gauge is generally pretty accurate about 1.5 hour into the burn. By then that top layer is mixed with the cooler lower level and the gauge will drop then start rising. The further away from the end burn time I get, the more I've relied on my temperature coming inside when deciding to fire. The flue temp gauge also has been a handy indicator of when to fire. I've seen the front gauge read 185 and only be getting 150 degree into the house. My top sensor on the outer portion of the tank towards the top verifies what you are seeing. I don't see much variation from front to back. But it shows those 100 gals of unusable heat. No biggie, I'd rather have those trapped btus than have to worry about sucking air.

It has been in the lower 20s and teens the past couple days. Wind blowing pretty good. Running the unit about 7 hours a day. Big difference in setting the tstat to 68 than 72. I'm pleased at it's ability to convert wood to energy. I wish I had radiant instead of baseboard. Ive consistantly been running it up to 200-205 to get me 10-12 hours of standby. House needs more insulation and more baseboard fins.

At what temp do you put in a full load to get in the 200*-205* temperature range without reaching boiling temps? I am sure some of the equation would depend on the load at that time, but ballpark would help me out.

 

[RowCropRenegade]

Sawyer, 190ish with a full load will take me to 205. That's well dried ash. I've hit 208 once and small clouds of steam was coming out the overflow.

Rick, i would describe the front gauge as funky as well. I'm envious of your ability to use that low of water temperatures. How often do you fire?

Today is the type of day where I was burning 10-15 gallons of diesel a day. 15 degrees with windchill of 0. Garn will run 8 hours today, maintaining 72 degrees inside.

 

[Sawyer]

Sawyer, 190ish with a full load will take me to 205. That's well dried ash. I've hit 208 once and small clouds of steam was coming out the overflow.

Thanks Reed, that gives lots of room for safety. Mostly hard maple here.

 

[bpirger]

My problem with a supplemental unit like that Rick is that once the DHW pump turns on to heat my indirect DHW tank, until the temp is met, which I have now at 115 but always had at 120, the pump will run and run.....eventually it will start taking the heat out of the DHW tank and into the system. Now, with all radiant, I indeed can heat the house quite great with 120 water from the Garn, and very well down to 110 for sure...and even at 100 degrees I'd be warm.

So my thoughts have me thinking I should hobble something together that once the DHW pump is on, and if the DHW supply temp is less than say 130 or so (i.e. Garn water is 130), then I should fire the oil boiler....which will heat up the the primary loop quickly enough to satisfy the DHW. Oh, but then I'll have the problem that the oil boiler will be trying to heat the Garn as well! So without shutting down the Garn pumps, as my Garn is plumbed into my primary loop as a secondary loop....so without shutting down the Garn pumps, I'll effectively never see the increased water temp...it will mostly run out to the HX in the Garn. Just another level of control...when does it end!?

Or I could just keep the DHW pump running for hours and hours....using the post DHW tank booster like you pointed out.

As for wood burning, I can easily heat the house now with 1 burn a day...but the DHW is the issue...after the stratification reaches the Garn supply. I do see the temps drop for the first while when doing a burn, just like everyone else, as the tank mixes. Funny though, while the front display is dropping, the supplied water is increasing. Call it what you want....a bug or a design feature, at least it is consistent and now understood.

It would be a straight forward matter to put some electronics together to have say 20 temp sensors and 12 variable speed pump controls/valve actuators. It would be GREAT to have full programmable control over all the pumps, all the valves, and direct feedback from all the temp sensors. All of these issues would be readily controlled then. And for about a dozen or so heating nerds around here, we'd be in happy city. I wonder how big the market is beyond that!

Thanks to all! Bruce

 

[Como]

My system is designed for 140-150 water as it uses radiators, so I should not have that problem.

The problem you mention seems similar to Solar HW systems where you might have to boost. An instantaneous heat unit, Rinnai etc would seem the best option. As you have such relatively high temps coming in, they would be able to boost it a few more degrees very easily.

 

[Como]

It would be a straight forward matter to put some electronics together to have say 20 temp sensors and 12 variable speed pump controls/valve actuators. It would be GREAT to have full programmable control over all the pumps, all the valves, and direct feedback from all the temp sensors. All of these issues would be readily controlled then. And for about a dozen or so heating nerds around here, we'd be in happy city. I wonder how big the market is beyond that!

There are systems that do that, for example:

http://www.tekmarcontrols.com/tn4.html

 

[bpirger]

David: Yes, I run the Tekmar 363 and 362. Together they are over $1500, and they only control two mixing pumps, two mixing zone circs, the primary loop pump, and the DHW. Now that's quite a bit, and I love them dearly....but they aren't inexpensive...and they don't really let me control everything depending on everythng else. Perhaps one can piece together a system using their integrated serial link, but it wouldn't be anywhere as easy as a single processor that could access all 12 pumps, valves, with all the integrated temp sensors. With my embedded engineering hat on, it would be a pretty simple matter to build such a system....and it would be GREAT for systems like these....as oposed to piecing together various mechanical relays, etc. I'm just dreaming a bit. When I first found the Tekmar stuff back in 2003 when I installed them all, I really thought it would be a great business opportunity to build such a system. I think it would be tough though to get accepted within the community.... Far as I can tell, Tekmar stands alone with their level of programmable controls.....they need a good competitor! I see the build stuff for Taco, Weil-McClain, etc.


Perhaps my concern about running the DHW pump endlessly (until I refired the Garn say) is just unwarranted. It's an 010, so it draws over an amp I'm sure....and it does start taking heat out of the DHW once the Garn supply drops down to below 120. Indeed the boost would not have much work to do, raising the temp by more more than 20F say.

It also seems that firing the Garn twice a day in smaller loads may also solve the problem....and there's a nice bed of coals it seems to fire the next load up too boot! It seems like the stratification level of 125 or so water reaches the supply in about 14-16 hours with the current load (about 16 outside tonight!)...and my feeties are toasty on the floor...so firing twice a day solves the mixing problem, DHW production, etc. Just uses a bit more fuel I'm sure....given the less efficient operation at higher temps.

 

[Como]

I have seen a TN4 in operation, the one I saw was using a heat pump rather than biomass. It had PV in the mix and I can not remember if it had Solar HW. If it did not it had provision for it.

That particular system was in a high end house in a Ski town, the owner could monitor the system remotely, ramp up the heating before leaving home so it was toasty when he arrived.

I saw it at an open house before everything had been covered up, it was being described as being green technology, but a 10,000sq ft house partly occupied by one family?

The amount of cabling they had in the house was very impressive, seemed more cabling than framing.

My guess is that the TN4 system was a very small percentage of the total HVAC cost.

 

[bpirger]

LMAO....green and 10,000 sq ft!

Sure, if money is no object, it is quite easy to build nearly anything....well home wise/HVAC anyways.

 

[Rick Stanley]

[Rick, i would describe the front gauge as funky as well. I’m envious of your ability to use that low of water temperatures. How often do you fire?]

It depends on the outside temperature, my demand at the time and the wood I have. MOST of the time I fire once a day.
But, what "firing" involves varies sometimes from day to day. For example: if we're having sunny days near or above freezing, I can draw the Garn down to 140 on the front gauge. That gives me 120* water coming into the house. Then I lose 10 more degrees across the heat exchanger and I end up with 110* to the radiation. On a sunny 30* afternoon I can keep the house at 70* with water that cool. But ,as we said before, can't make dhw
With the wood I have right now, mostly soft maple, I have to fill (actually only1/2- 2/3 full) the garn 3 times to raise the temp on the front gauge to 190-200.

Then when it gets colder like this past week, lows in the single numbers and highs in the 20's and no sun, I need 130-140 degree water coming to the radiation to keep the house warm. So I fire twice a day but only have to load the garn once or twice each time.
When it gets really cold I'll have to "fire" twice and load three times on each firing. Last year I had some red oak seasoned inside for two years. I could fill the garn one time morning and night during all but the few very coldest days. Kind of wood makes a huge difference.
Last year also, I had 24 inch wood. This year it's 30. That's got to make a big difference. So, my system lacks the automatic-ness of some of these guys, but I'm here most of the time so it's working out ok. Still got to address the dhw issue..................

 

[Como]

Do you fire in the summer for DHW?

 

[Rick Stanley]

Because of health issues, I've had a hard time providing enough wood for the heating season. So, no, I haven't burned in the summer yet, but I hope to do so next summer.

 

[Como]

So how have you heated your hot water in the summer?

My idea is to use wood when I know I have a high demand, and i think the combination of heat and DHW load in the shoulder season will be enough to use just wood.

But in the summer/low DHW demand I will top up with my back up Propane Boiler. At least the water which is very cold out of the ground will be pre heated by what is left in the Garn.

 

[Rick Stanley]

I'm keeping an oil boiler hot with my garn through a flatplate hx. The oil boiler has a coil in it that is piped up to a 40 gallon storage tank with a circulator in the line that is controlled by a thermostat on the tank.
The way I have it set up right now, I can either burn oil or wood. No automatic back and forth. So in the summer, I burn oil for dhw.