Drawing From Storage - Pulling Through Boiler?

[maple1]

So now that the heating load is off (or mostly off), and I've been burning for a little while just to heat DHW most of the time, I've noticed something about my setup that I didn't notice in heating season. When the boiler is out & gone cold, and I get a call for heat that sends hot water to a zone (right now my sidearm), I'm pulling some water through my boiler. I think most is coming from storage, but it is enough to put most of the now-cold boiler water through my sidearm & partly into storage. So I'm losing heat. I checked out the diagrams in the 'simple storage' sticky, and I can't figure out what would stop the same thing from happening there too - although I'm not sure what the little square doohickey is in the top of the wood boiler supply piping. I could stop this by closing the ball valve in my boiler supply pipe after the boiler has cooled off but I'm not fussy about that in the event I forget to open it some time I'm building a fire in a hurry - although my dump circuit would still be active. I thought the LK810 would prevent some of this, but it goes right through it - which kind of makes sense too though as it is also supposed to allow convection flow in power outages.

So for starters, why wouldn't this happen in the 'simple storage' sticky scenario?

 

[Coal Reaper]

I have thought about that for my instal as well but nobody else seamed to mention it so i havent worried. It would be return water temp going through boiler which i intend to keep around 140 with bumble bee. Also my head should be decently high due to several 90s and about 50' of piping in the boiler loop. 1.5" diffusers into tank as opposed to 1.25" everywhere else. Flow should preffer the path of least resistance right? I still see some going through boiler. At least that will prevent condensation on warm humid days...

 

[maple1]

There is a bit of a good side to this as I can pre-heat my boiler before building a fire by activating a zone valve - I didn't realize I could, before this. And yes it should prevent any condensation issues. I'm pretty sure most of my flow is following my path of least resistance, which is through storage. But I'm still getting enough flow through the boiler that every time my sidearm & DHW heats, my boiler also heats - puts a damper on boiler mileage between burns in the summer I was hoping for...

 

[ewdudley]

So for starters, why wouldn't this happen in the 'simple storage' sticky scenario?

It says so right in the 'simplest' theory of operation. When heating from storage, "There is no flow through either boiler.".

 

[Coal Reaper]

Maple, did you put ur loading unit right at the boiler return? I positioned mine off the ground a ways. I wonder if that would make it more difficult for flow. When looking at other units in operation i got tired of seeing everybodies @$$crack when they squatted to look at the temp guages on it. I display enough of my own crack around here. Dont need anybody elses!

 

[BoilerMan]

I display enough of my own crack around here. Dont need anybody elses!

LOLOL, same here!

TS

 

[maple1]

My loading unit is mounted low, right outside the return tapping. The way it's positioned between the boiler & storage, I can't see the thermometers anyway - so no crack issues, from that at least. (I also put tridicators in T's at the supply & return tappings for easy viewing of supply & return temps from the front of the boiler).

I think the only way to stop this pulling through boiler would be to put a zone valve (NO) on the boiler supply line (just downstream of the bypass T) and control it with a probe thermostat/aquastat with the probe mounted on the piping right at the supply outlet. Then when the boiler gets to say 140 on firing the ZV will open for proper heat flow out of it & close again when it drops below that when the fire goes out - and also open on power outage. But I don't think I'll be going to that trouble at this point - plus I had a hard enough time finding a NO ZV for my 1" dump circuit let alone a 1-1/4" supply line that you'd want to be sure could flow lots of water when burning hot.

 

[Coal Reaper]

agreed. i will wait and see how much of an issue this becomes for me. how far of a run do you have from boiler to storage and back?

 

[hiker88]

One of the Innova guys on this forum had the same issue and he was using the a Tarm piping schematic. I think after some troubleshooting with Tarm, the ended up going with a zone valve as suggested here. I can't remember if it was NO or not.

I'm just going into my first season of dhw only use, so I'm curious if I will have the same issue. I'm guessing yes...

EDIT The post I'm talking about was in the last month or so. I'll try to look for it later if no one else finds it.

 

[maple1]

They're right next to each other. No more than 6ft. on each with a couple of 90's & couple of 45's in between.

 

[hiker88]

This is the post I was referring to:

https://www.hearth.com/talk/threads/termovar-loading-unit-ghost-flow.106006/

 

[maple1]

Huh - I even replied to that thread (& forgot about it) that I didn't think I had this issue. Turns out I did.

Not sure whether to continue with this thread or resurrect that one - flyingcow (if you're reading), what model/size exactly of zone valve did you end up putting in? I think I'd be looking for a 1-1/4" NO one with good flow - they seem to be rare. Are you happy since then with it? This is now in the 'possible future upgrades/improvements' part of my brain...

 

[kopeck]

I had the same problem.

When you installed the loading unit did you use the solid plug or the check valve? The check is used when you have your storage piped up as the no power heat dump, which from what I understand takes some real plumbing magic to make work. Most folks either tap into an overhead zone or add a separate array to do the same thing and it's much simpler.

So the solution is to remove the check valve and install the solid plug.

In my case it came from the dealer with the check installed. It would pull through the boiler when on storage, which was annoying but the bigger problem was when the boiler was coming up to temp the check valve would swing open & closed and create some good noise and some of my pipes would jump! The solid plug fixed all that. It's really easy to replace, you don't have to drain your system, just use the ball valves in the inlet/outlets.

Here's the thread from last year:

https://www.hearth.com/talk/threads/termovar-loading-unit-on-tarm-solo-innova-causing-thumping.84305

K

 

[Coal Reaper]

in my case i have 13' of vertical storage that i hope to rely on for gravity circulation overheat protection. i dont think i want to give that up by removing check and adding that solid plug. assuming i didnt have noise and pipe jump from check valve, i would be more inclined to instal N.O. zone valve. eagerly anticipating what i will experience in the next few weeks...

 

[maple1]

Pretty sure my 810 didn't come with a plug. I'll have to dig the box out & look in it to make sure - but also since the Varms are a bit different in that they can't idle, I suspect it was maybe shipped without it so someone couldn't disable the gravity circulation feature. I'm not sure I want to disable that dumping-to-storage feature either - even though I do have a dump circuit too. kopeck - where does your overheat circuit flow go or how does it get back into the boiler? On further thought I think if I were to plug the 810, I would also disable my overheat/dump circuit too as the flow through the dump zone would eventually need to re-enter the boiler somehow though the 810 & into the return tapping.

 

[kopeck]

Are you sure your boiler can even dump to your storage when the power is off? From what I understand it's not a terribly easy thing to do. You need your piping to be just so and some of your storage needs to be above the boiler.

I dump into an array I built, it's just fin tube sitting above my boiler. The water exits through a tee off the hot manifold via a NO valve and returns through a tee in the boiler drain. You can see my array here:

It works, I've shut my boiler down a couple of times with the fire going to test it out the it's pretty amazing how quickly the water thermosiphons through.

The LK810 should have come with the plug, now if it made it to you from the dealer is something else entirely. I understand you not wanting to disable the check valve but I really don't see how you are going to overcome the flow through the boiler with out doing so or adding an extra valve and coming up with a way to control it and still not disable the thermosiphon to storage.

K

 

[maple1]

Ah, OK - overheat back through the drain valve. That makes sense.

Yes, quite sure I get flow to storage in a power outage. My storage & boiler are practically next to each other, the top of storage is almost a couple feet higher than the top of the boiler. Tested on a power outage, I had flow going two ways out the top - up through my dump valve into my house via upstairs baseboard (I wanted to use my existing radiation & dump heat into the upstairs), and out the normal way to storage. I don't know how much was going each way, didn't do any temp measuring - but all in all it handled the power outage more than adequately. Since mine can't shut off a fan or close a draft door to slow the fire down with loss of power, I want to keep all the overheat & dumping ability possible. And I like redundancy in important situations. I know how I could get this done with something like a Johnson A419 plus a NO zone valve - but larger NO zone valves seem to be an oddity, here at least.

 

[kopeck]

I know how I could get this done with something like a Johnson A419 plus a NO zone valve - but larger NO zone valves seem to be an oddity, here at least.

Check out Belimo, they pricey but really well made. They're also a ball valve so 100% shut off and they switch from NO/NC with a flip of a switch.

K

 

[Armaton]

You could also just heat storage only with the boiler circuit, and utilize a different output from storage for heating and DHW. You would still get the hottest water available from storage, and would stop the flow through the boiler circuit, and still maintain thermosiphon.

 

[maple1]

I think you would still pull the now-cold boiler water into storage? (And replace with warm storage water).

Maybe not as fast but it would still get in there?

 

[ewdudley]

I think you would still pull the now-cold boiler water into storage? (And replace with warm storage water).

Maybe not as fast but it would still get in there?

The key is that the water in the boiler is cooler than the water in the tank. As long as the relative buoyancy of the tank water column is greater than the pressure drop of pulling through the tank portion of the parallel circuit, then there will be no flow through the boiler.

As you have discovered, if the resistance through the tank portion of the parallel circuit is high enough, then the buoyancy of the heated water is not enough to prevent parallel flow through the boiler.

The easiest thing to try might be to reduce the flow to a minimum so as to reduce the pressure drops.