Wanting advice! Owb and adding thermal water storage

[ac2linville]

My current setup is a Hoss 300he and 1” thermopex with about a 70’ run to my house. Once inside I run another total of 60’ of 1” copper type m in a loop first stop is my plate to plate heat exchanger for dhw and then to my 85k btu air to water heat exchanger in my furnace plenum. It’s been setup this way for a few years and has been great. I’m wanting to add some water storage with a diy built tank and nice epdm liner inside my basement and copper coils to reduce the thermal shock going back to my owb. My thoughts were to add a 1” manifold with 4-1/2” copper coil lines each 50’ and then from their my run to both heat exchangers and before returning directly to the owb it returns to the water storage to another set of 4-1/2” copper coils to reduce the thermal shock back at the wood stove. And to mainly reduce the cycles and save wood and all that would be on one loop. Or I add another pump inside my house to have it run continuously with the other set of 4-1/2” copper coils 50’ each in length on its own separate loop to collect the heat from the thermal storage. Trying to find ideas and if any other info needed please ask as I feel like I’m writing a novel.


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[maple1]

If it is all one simple loop, then any time you are running the loop with a cold boiler you will be sending stored heat out to the boiler & outdoors.

 

[E Yoder]

I have my doubts adding storage will significantly change the efficiency of your unit? I think it's not a gasification boiler, but I could be wrong.

 

[maple1]

Ya, I'm not sure about using storage with OWBs in general.

The whole point of using storage is to burn the boiler wide open when it is at it's best combustion efficiency, sending excess heat to storage, then coast off storage when the fire burns out, until the stored heat is depleted.

Which means there would be periods of time the boiler will go cold. Will it be OK to let it go cold? Will anything freeze?

Then there will be quite a period of time when starting a burn to heat everything up again. Does the boiler have good heat transfer efficiency? If not, you will be losing heat up the stack when that is going on - and when charging storage at wide open burn.

Might be an advantage for some OWBs, but an ordinary simple water jacketed one, I'm thinking not. (Don't know what the Hoss is). Plus the possible freezing thing.

 

[ac2linville]

I would say that I run my owb 24/7 without ever turning it off. Currently aquastat is set to 180f with a 10 deg shutoff at 170. When my inside heat exchanger (furnace plenum) kicks on to call for heat I have a delta of about 20-25 deg colder going back to the boiler. So as it gets colder in our winters my furnace can cycle on and off about 4-6 times before my owb needs to fire up again. I’m trying to avoid thermal shock and I want to add a buffer tank to my system so it’s not as cold going back to the boiler. I’m just wanting to mainly cut down on so many cycles my boiler kicks on and off and would prefer longer burns to be more efficient. So it always seems like I’m flip flopping on my own ideas to get this done. Thank you again for taking your time


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[coolidge]

Honesty, I have 330 gallons of storage for my OWB and there is very little difference in wood consumption while I am using it versus not using it. While using it, I have 180 going in but 160 coming out, so always a delta t.

 

[maple1]

Why the big concern about thermal shock?

 

[ac2linville]

I always like to learn more and it’s winter time here so I get a little more time on my hands. just trying to see if I can make my system more efficient and save on the wood consumption. Plus I like having a project to do. As well after reading that a system is more efficient with the longer burn times (creosote and useable btu’s). I was thinking the less cycling would be the better option for my owb. But hey that’s why I’m on here lol.


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[maple1]

No doubt there are potential gains by keeping your boiler burning all out without idling. Idling is a waster. Just not sure when it comes to different kinds & designs of OWBs on whether it would be 'worth it'. Also one other side effect of storage, that is usually a benefit, is it usually sends colder water back to the boiler. Not warmer. Coolest water back into the boiler for as long as possible is another efficiency gainer. But the boiler has to be able to handle that cold return water, usually with some sort of boiler protection or boiler bypass setup.

 

[hobbyheater]

In the early 80's, 1049 imperial gallons of storage was added to a boiler like the one pictured below. The boiler was a cast iron down drafter, somewhat efficient for its time. With the addition of storage to this boiler, its yearly wood consumption was reduced from 16 to 10 cords a year. Also on storage you should be looking at 1,250 gallons of storage to gain any advantage on storage.One of the down sides to adding storage is the inside of the boiler and chimmney is really going to cresote up so good boiler protection is going to be needed .
The epdm liner that you spoke of is not the best choice. Contact American Solartechnics. They have better liners and offer complete tank setups. http://www.americansolartechnics.com/

 

[warno]

I added 750 gallons of storage to my homemade OWB and it made a huge difference in wood consumption the first year used. But I also switched my burning techniques from letting it run idle to batch burning.

Here's the threads I made of my improvements to my system.

Starting my "storage and replumb" project

I decided to put in a storage tank and replumb everything from last year and plumb the house in the loop as well. Here's my storage questions thread https://www.hearth.com/talk/threads/help-with-storage-plumbing-2-0.154285/ And my last year's project thread...

hearth.com

My replumbing project

The end of last season turned into a nightmare at best. Over heating issues led to cavitation issues. I couldn't get enough heat out of my boiler to save it from going into idle mode, No matter what I did. Some of you may remember my threads on over heating and cavitation from last year. So...

hearth.com

 

[peakbagger]

Unless you go to batch burn you are not going to gain much. To batch burn a typical OWB you would need huge storage. You mentined off hand EPDM for a liner. It typically does not work well at elevated temperatures. Seam welded PVC is the preferred material.