Trouble getting storage up to temp

Doesn't seem to add up. Can you do a bare bones schematic of the system piping?

I don't think I'd say the top of your tank is not that warm (if it is 187 - I call mine hot when it gets to there), but I do think your lower temps should be higher by the time you hit idle. Does sound like it's not moving enough water - if return from storage is 155, that's a 40° delta T through the boiler. What size is the Thermopex?

easternbob said:

Here's a bare bones schematic. There are other vales that I didn't bother to show.
The cold temps of the last couple days have been a good test. I realize that while the house is calling for heat the tank is going to charge much slower and result in more mixing top to bottom (warm return temps).
But what is bothering me is the boiler idling at 195 and the top of the tank is not that warm. Seems like something is not right.

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So storage is 65+ ft away from boiler? What is diameter of pipe between boiler and storage?

Check the return temperature to the boiler. IR meter would be nice, but if you can put your hand on it for a few seconds it is something like 140 degF and if you can't hold on without burning you hand it's more like 180 degF or higher.

Yes measuring return temp at the boiler inlet might help. Seems the 009 should do it, with the 1". I don't think the pipe itself would present more than 4' of head. Not sure how much head the Danfoss presents - but opening that bypass all the way should find that out in a hurry. Might still have an air issue?

EDIT: Also, you're seeing pretty good stratification for a tank that size sitting horizontal. I would have expected to see a lot more mixing and not very much stratification if the 009 is flowing what it should be able to flow.

I suspect your return temperature is high because the Danfoss letting significant flow in through the bypass leg (the leg from boiler supply to the Danfoss, not the other bypass leg). Depending on the exact Danfoss model they have been known to do a poor job if there is a big difference between the resistance of the bypass leg relative to the load loop. The load loop resistance is fairly high in your case and you may need to install a 'balancing valve' to restrict flow through the bypass leg.

Also it might help to set your 'launch temperature' up high with a minimum hysteresis so that you only activate the 009 when supply temperature is near your desired storage temperature. If the 009 runs constantly it will fill storage with not so hot water the first time around and then there may not be enough flow to carry all the heat the boiler is producing when the return temperature for storage is elevated on the second or third lap through storage.

easternbob said:

Do you think I could get away with a ball-valve there that was cracked open??

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Where is the ball valve set now? Full open?
Also do you have adhesive between the temperature probe and the tank on the ones you have "glued"? Might be giving you an erroneous reading.

If your pump is not at its lowest speed i would set it at the number one setting before I did anything.

if you have valves left out of the drawing you should add them to the drawing.

Using my simple plumbing- a B+G 3 speed circulator pumps between both boilers to balance the
water temperature when burning wood and coal.

Why is it you not have a pump loop with bottom draw(sump fed) between the boiler and the tank?

More than anything I think you have a fluid short circuit there.

easternbob said:

I've got my launch temp set at the 170 (the max) right now. Will have to check the hysteresis, I think I might have that at 2.

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With storage being remote and therefore with flow being somewhat limited (most boiler-storage loops can flow in excess of 14 gpm with no problem), I would be tempted to add an aqustat on the boiler supply that would disable the 009 whenever supply temperature is not as high as your target storage temperature. This in effect would be to raise your launch temperature up where it needs to be as opposed to where the EU thinks it should be.

This would maximize the deltaT through the boiler and through the boiler-storage loop and should prevent idling for as long as possible as the burn cycle progresses.

leon said:

Why is it you not have a pump loop with bottom draw(sump fed) between the boiler and the tank?
More than anything I think you have a fluid short circuit there.

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(The Danfoss is a high Cv mixing valve that should (in theory) supply 140 degF flow to boiler return. If it is allowing too much flow through the bypass leg from boiler supply, then yes, there is a short circuit to some extent.)

I see a valve in that one, on the bypass loop, that wasn't in the first one. I suspect ewdudley has it, in too much flow going around the bypass loop. IMO a flaw in the operation of a Danfoss. If there is indeed a valve there, it should be throttled.

easternbob said:

Maple, we must have posted at the same time.
Yes I updated my sketch to show all the valves. I forgot to label that the valve above the Danfos is wide open. The valve that is in the by-pass loop around the Danfos is just cracked open a little bit (maybe 1/8 open).
So you think I should throttle the valve above the Danfos? Any guess as to how much? I'm looking for a solution that does NOT require me to remember to open and close valves (human nature to forget....) but if that's what it takes.

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Definitely should be throttled. Not sure how much though - that would be trial & error. Plus I've never worked a Danfoss before - just read a lot about other people working them. If you can watch your boiler supply & return temps at the boiler, you should be able to dial it in and your problems should all go away. I think I'd start at only cracked 1/4 open & see what happens - but others will likely chime in on what they run.

Ball valves make a terrible throttle. Even at 1/8 open you could still have too much flow. You'll know immediately if you close it to much as it will not activate the thermostat on the next cold firing. Yu could experiment! Remember, no flow for a short period of time won't do any damage but cavitating the pump for an length of time could cause damage.

Tell me, will achieving higher temperatures from top to bottom make a difference in your firing schedule? Will you be able to store enough BTUs to change your firing from two fires a day to one or from one fire a day to one every other day? Those last BTUs come at a high price.

easternbob said:

Not certain how this would help with idling? I've had the boiler idling now when it hit it's max temp of 195 but yet the bottom of the tank is 20-30 deg. below what I would like to see. How would shutting the pump off that would move some of this cooler water out of the tank help the issue?

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You're right, if the 009 is putting 8 gpm or so through the boiler and if the Danfoss is drawing completely from storage then you would expect to see no more than about 18 degF temperature rise from return to supply. If the Danfoss was performing as intended, that is. We suspect that the Danfoss is allowing hot supply water to circulate through the bypass leg and adjusting the balancing valve above the Danfoss should help cure that problem.

The problem I'm talking about when I suggest raising the launch temperature is what I call the N-laps-through-storage problem. On the first lap the Danfoss should flow 8 gpm or more of 140 degF into the boiler return. At 75000 btu per hour (on a good testing day) the EKO can only raise 8 gpm of flow 18 degF, so supply temperature to storage is 158 degF. On the next lap return temperature is 158 degF and supply temperature is 176 degF. On the next lap return temperature is 176 and supply temperature is 194 and the boiler idles. So if your target temperature was 185 you're stuck.

But if you set your launch temperature to 185 degf or so then there will only be one lap through storage. When the 185 degF water comes back around storage will be filled from top to bottom with 185 degF water and you'll be stuck right where you want to be. When my system gets to this point I don't idle, I just shut the combustion fan off and let the fire go out.