A 5,000 gallon storage tank, Not dialup friendly

[Justburnit]

I have built a 5,000 gallon, non pressurized storage tank. This tank went through a few design changes before construction started as well as a few more during the build.
I originally researched building a masonry stove but my house is large and long. I had been using a Defiant wood stove for supplemental heat but the issue I ran into is the south side of the living room had 54' of floor to ceiling glass. Old Anderson ⅜" glass. With the Defiant burning happily away it would be 75° near the stove but down to 40° near the windows. I was first looking at ways to distribute the heat. Then how to store and distribute and could not come up with a suitable way to utilize what I had. It became time for a rethink, and this is the direction I went.

The beginnings.
I decided that I did not want to install the new boiler in the basement, long term forecast is that my bad leg won't get stronger and my back will get worse so needing to go up and down stairs repeatedly 10 years from now was not an attractive idea. I also eliminated the idea of an outside boiler. I do not want to wake up and go out to load a stove on a frigid morning.
So we went with a new addition, great the house is too big as is. But an addition it will be.
The original tank design was to build a block foundation on two walls and utilize existing structure on the inner walls. I was not sure how well I would like this idea since one wall was a non mortared piled stone foundation. I figured I would just taper that wall of the tank so it would not impose a sideload on that wall. As I got to digging and was down in the hole looking at the house I could see that I had left a basement light on. I should not be able to see that between the top of the foundation and the sill of the house. Might be why a marble on the floor picks up speed as it rolls towards that wall.
Redesign time, It was decided to go with a poured concrete structure on all 4 walls. Big cost increase but had to do it.
Well to start with I had gone out and scrounged a few pieces of 3" thick blue foam,
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With the change from block wall to poured concrete I decided to go with the Quadlock ICF system,
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I sculpted the ground in preparation of forming the footings,
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The way I did these footings was to pour directly between the foam so the sides of the footings are insulated,
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I was also going to do a monolithic pour,
the footings and walls were poured all at once so there would be no shear line.
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These forms go up like Lego blocks, I hadn't played with these in decades,
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The Quadlock system allows for different concrete and foam thicknesses,
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Ready to pour,
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The pour was done on a chilly December day in 2006
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Chilly enough that it was snowing while the truck drove away, But the next morning I was back at it adding another 3" of foam to the 4 ¼ that was there.
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Continued, Part 2 in an hour or so,

 

[Justburnit]

Tank build part 2
With the tank walls poured, additional foam added to the soil bearing walls and it all backfilled I then took the time to get the house set back on the new foundation. Lets see if the front loading washing machine can settle these walls.

The next step covered here was to grade the soil and install 6" of foam for the floor of the tank.
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At this point it was time to shut down for the winter.
It wasn't till August that I could resume the project. I had researched a precast top, an ICF poured top and numerous other options.
I chose to go with wood, is this the best way, I doubt it but the next section has many compromises due to available resources where I live.
So My next step was to lay out the floor joists,
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This structure was built in place then hoisted and hung so I could work on the tank lining underneath.
I am jumping ahead to the tank liner,
This first one shows the liner being brought up to the sides and starting to tuck the ends in place.
The inside of this tank is 14' x 10' and 5' deep This is a pretty good size of rubber to wrestle around.

One detail to note are two dark shiny spots on the wall on the right side of the pic, These are aluminum weldments I made for the thermocouples, there is a plastic tube through the concrete that the sensors get inserted through and these transfer the surface temp of the tank pretty well, I think.
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The sides are hung and corners need to be folded next.
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Once the corners were in place I set the through the wall fittings, Here I am setting the tank fill and drain fittings.
Both fittings are capped but the filler has two small holes drilled to act as vents.
Also in this picture, the white lines are a rope webbing intended to hold the top liner up, this did not work at all.
I ended up making a temporary structure of 2bys that worked well.
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After attaching two sides of the top membrane under the sill plates I then set the deck structure down,
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With the inner two sides of the top bonded and clamped in place I then gripped a corner and pulled tension so I could set the other sides,
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Once all the sides of the membrane were clamped and bonded I again picked up the structure and inserted a continuous layer of 3" foam.
This provides a full insulation layer with no thermal breaks between the structure and tank.
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At this point I cut through where the service hatch is to be and locked the top in place.
I used strips of composite deck material held up with 6" stainless screws into the joists.
This holds the foam and membrane up as well as providing me with hardpoints for a rack system to use later.
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And now I had to work with a big compromise, I sure wish I could have had someone spray foam the insulation in the floor but the only Quote
I could get was at a stupid price over $22 a square foot.
So I used the foam I had and cut, fit and sealed all the bays in the floor.
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I then installed the floor, this also was bonded and sealed,
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I will jump past the building of the structure, the original intention was to use Structured foam panels for the walls and roof,
I need to contain cost and went stick built with blown in celulouse.
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With a shell up the Tarm was set in place,
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A sprinkler system installed overhead with heat sensing alarms.
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It was now time to play in the rubber room,
All through tank fittings are at the top of the tank,
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I made a rack that the heat exchange tubes all hung on. For economic reasons I could not afford Copper so the system was built with Pex,
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Not all the tubes are in here at the time of this shot.
The heat transfer are 6 100' loops,
Two loops for the solar system input.
A 100' loop to heat the Spa,
A loop to preheat the water going into the DHW tank,
A loop for an icemelt system.
And a few spare inputs and outlets.
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And then the glorious day in early January when we chopped thorough the ice on my pond and pumped the water in,
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Now about this time I must have lost interest in shooting pictures. With the tank full of 34° water I did a bunch of pipefitting, filled the boiler and fired the system up.


Keep in mind, I had not found this forum. I am self employed and built the whole system with money out of pocket and between customer jobs. When I work on the house I do not earn money, this takes a toll on you.

 

[sdrobertson]

Wow This is very impressive. Very nice job.

 

[Justburnit]

My house has both radiant and baseboard heat. When I moved in here 11 years ago it was forced hot air, The system was in horrible condition. At that time I installed a hydronic system with a system 2000 boiler. Over the years much work was done to insulate and air seal the house cutting my fuel use to less than a third of when I moved in. During that time the Radiant was added in. I can switch between systems and in reality the baseboard works just fine with water temps down in the 130° range. The circulator just runs a bit longer.
At this time I use the baseboard as a kicker to bring up the house temps when the radiant is either stumbling or has been caught be a fast drop in outside temp at the end of a sunny day.
The baseboard is also useful in bringing the house up quick when we return from 3-4 days without burning wood and the storage temps are down.

 

[tom in maine]

Impressive project. I would keep an eye on the EPS blocks. They usually do not like high temperatures. (above 140-160F).

 

[Justburnit]

My original desire was to install a layer of Hi R foam on the inside of the tank. This would have been to protect the EPS, for some reason I never installed that layer.

I generally use the mid 160s as an upper temp and depending on demand it drops 10-15° before firing up again. I am building a heat exchange tower that will mount on the top cleanout of the Tarm to capture the waste heat. This will be a tube-air exchange and will either use a flat plate or direct transfer to the tank. Not decided on that yet.

The Pex tubes in the tank have about an 8° heat loss on exchange, this is a bit more than I expected.

 

[pybyr]

! Applause !

What an impressive piece of ingenuity, determination, and craftsmanship

 

[stee6043]

Awesome project! Nice photo-journal of the whole thing too.

How did you determine how much pex you used as heat exchangers in the tank? Very cool setup....

 

[SolarAndWood]

Exceptional project and documentation. Thanks for sharing it. Have you measured standby loss, temperature gain on incoming water to DHW, effectiveness of the solar collectors on the tank, etc?

 

[Nofossil]

I am very impressed - nice job! Seems like you really thought this through.

It will be great to get performance data over the years.

 

[Northwoodsman]

Very impressive project!

Nice way to "kill two birds with one stone" (storage and foundation for new addition).

I have a few questions about it:

1.) How did you determine what size tank you needed?
2.) How did you determine how much PEX you needed for the HX?
3.) Did you perform heat loss calculations (BTU loss) on the area you are heating?
4.) How is the system working and do you have any performance data you could share wih us?

Please keep us posted on how things are working out and the changes you make along the way.

NWM

 

[Justburnit]

Thank you guys,

How did you determine how much pex you used as heat exchangers in the tank?

I do not recall where I got the numbers I used in calculation but they came up with 4 100' loops. I built it with 6 loops and glad I did. The return temps on the loops are not much higher than the top tank temp, 3 to 7° or so.
Mid way through last heat season I realized there was a fair amount of stratification in the tank that was hurting performance, I had a mis belief that with my coils around the perimeter of the tank that it would mix the water as it is heated. Not.

To deal with this I used a set of ¾" tubes that were fitted, one to the near side upper and the other to the far lower of the tank and fitted a bronze 006 I had to mix the water. This works well. I now get much less difference top to bottom in the tank when heated giving a much improved output temperatures.

My next step is to install a large flat plate in this loop and build a tower that bolts on top of the cleanout on the Tarm wit6h a tube type exchanger as a second heat output. This should raise the efficiency of a burn by a great amount.

Have you measured standby loss, temperature gain on incoming water to DHW, effectiveness of the solar collectors on the tank, etc?

The standby loss is about 10° a week at 150° tank temp. I am very happy with this considering my 70 gallon Vaughn DHW tank looses over 15°a day at 130° tank temp. Not impressed.

My preheat loop for the DHW has a single loop of ¾ pex, this underperforms and needs to be changed. It does however serve a propose, I have a small circulator to keep warm water at the showers, the return from this goes through the preheat loop. this does a great job of keeping the tank hot during the winter.

The solar system is a sore subject, it is an Apricus 30 tube array. It was subjected to freezing temps before installation that damaged it according to the manufacturer but the American Distributor up in Maine has refused to provide warrantee replacement. It occasionally provides afternoon shower water for the two of us but never enough heat to transfer to the big tank. The original intention was to expand to a 60 tube system but I will not spend another nickel with Apricus.

It will be great to get performance data over the years.

I have a number of thermal sensors and can move them around to different places in the system. I feel this could be improved on especially if I was set up for logging data on a laptop.

I have learned enough to make a number of changes, some done and a fair amount of to do projects.

The first important thing I did was to convert the Thermovar from a 3 way to a 4 way valve,
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This was done by machining a Delrin ring that closes the bypass as the unit opens the return flow. With a single 007 pushing water into the Tarm this greatly improved performance of the system.

This summer one of the first changes will be changing the water outlet on the Tarm Solo 30. One big issue with the Tarm is very poor internal waterflow. The water short circuits within the boiler.
There are a few here that have noticed knocking in their Tarms with a hot burn going, this knocking is a hot area up in the front corner under the blower. There is no water flow in this area so it boils in that spot. Tarm knows about it. I will now add a new outlet on top through the removable hatch that is intended for the DHW coil. This will draw water from the front corner so the internal water flow will be more even.
The next change will be the added heat transfer on top of the Tarm. With the best I can estimate my Tarm is at best 40% efficient. A far call from the manufactured claims. Most of the Solo series heat transfer is from the wood chamber to water, not from the tubes in the hot section. I am tired of seeing 500° plus flue temps and barely getting heat out when there is a small amount of wood in the chamber. This will change.

I have a few questions about it:

1.) How did you determine what size tank you needed?
2.) How did you determine how much PEX you needed for the HX?
3.) Did you perform heat loss calculations (BTU loss) on the area you are heating?
4.) How is the system working and do you have any performance data you could share wih us?

Some of this is partially answered above,

1, The tank size was selected intending to provide a longer time between burns off season. This almost works, I will give me 4 days of heat when the temps are around 35° or so. the issue I run into is putting heat back in. When the Tarm cools down it takes a full half day of burning before it puts out heat. As mentioned above this is being addressed. Due to this we found we needed to fire the unit daily. Frustrating when it is around 50° out and the house does not need heat and most of what it gets is the massive heat loss from the Tarm itself to the surrounding air.
I will be installing a forced air duct to move that heat to the far end of the house.

3, This was originally done by the plumbing contractor whom installed the first system, I think he just winged up with estimates as he looked around. I do have the Wirsbo software and personally this house has had so many build issues that I can not get what I call, "Good numbers".
I realized after watching the System 2000 for years and working from it's estimated output with different nozzle sizes and determining the duty cycle and fuel consumption to come up with better numbers for what was needed. Simply put, this house needs allot of heat if it is cloudy and well below zero. The sun helps allot here. Cold days, easily 30K an hour. More with no sun. If it stays around 20° and above the system has an easy time of it.

Hopefully I have answered most of the questions, I will add more when my mind lets me.

 

[Wet1]

Nice work and interesting read... thank you for posting!

 

[DaveBP]

Charlie,
Do you have a thermometer on the return water into the Tarm?
Do you know the temp of the water actually entering the boiler? Be interested in how your delrin ring affects this part of the formula.
What temp is the thermostatic unit in your Termovar?

I was at first alarmed by your mixing of the tank water. This eliminates the possibility of counter-flow heat exchange between the PEX and the tank water, if your tubes are arranged to take advantage of it. But after a little thought (always my last resort) I think it is probably well that you do mix it. If you're getting 160F top to bottom now, by letting the tank stratify you would have much higher temps in the upper water. I believe you would then be collecting data on the long-term service temperature limits of polystyrene.

Do you pour the whole height of the wall at once or gradually in lifts to limit the pressure on the EPS forms? Never messed with ICFs. Any rebar, mesh or fiber?

Thanks for posting such a thought provoking project. Great to see someone grab his tools in his teeth and attack a big dream.

 

[Justburnit]

Hi Dave,
I have 4 water temp probes that I move around between thermowells as well as surface mounting and also use an IR meter for quick checks.
By default I monitor the manifold where the pex loops enter the tank. This allows me to understand much of the performance when I am wither loading the tank or just drawing heat from it.

The Thermovar has, if I recall a 72°C element. At the start of last season the performance was real poor and I found closing the bypass manually would help. My big issue last fall was even though I ordered cordwood in March, Delivery did not start till August. I did not have nice dry wood so the Tarm just would not make heat. I actually removed the element from the Thermovar and manually valved the operation keeping return temps above 60°C and it started making heat. The Tarm can be very frustrating when it has 500°+ stack temps for hours and will not put out hot water.
Adding the sleeve in the Thermovar allows the bypass to be opened up during startup and once heat comes available it now moves the water out into the system, without throttling down the bypass.

My reason for mixing the tank. When I was doing a burn the top of the tank would climb up to say 160° while the lower part was about 145°. Within hours of the end of a burn the top of the tank would drop to the 140ish range that the lower part of the tank was at. Morning tank temps were around 130° and heating performance was reduced.
Now with mixing, the whole tank is at a higher temp at evening shutdown and overnight it would remain in the 140s or low 150s. The Tarm responds to the higher temps much better during morning startup. When the core temps in the Tarm drop the unit is a real pig to get back up and performing. I sure wish it would burn overnight.

Tank, the polystyrene is supposed to be serviceable with temps into the 180s. I have run test pieces above that but they did not have compression against they so I do not know the true limit of what I have. If the insulation fails it will induce the concrete to be more thermal mass. I still have 7" of foam to the earth and a few inches to the basement. I have monitored surface temps in th basement and they have been right at ambient. I would expect a small rise in surface temp with insulation failure. On the outside I had hard frost right to the wall. I did not expect that.

Above the tank the floor is cold, it will actually be a few degrees below room temp, There is an airspace between the top of the foam and the subfloor. Clearly I could use a bit more perimeter insulation.
At this time there is very little insulation on top of the service hatch to the subfloor. This is where the cats sleep.

I have rebar at every foot around the tank. Multiple bars down low and just single up in the higher rows.
The pour is done full height in one session. If I recall you can do a 12' pour in one session. The wall under the old house is 12" of concrete with a 12X24 footing. Took a bit getting used to seeing 50 pounds of foam shaken by tons of concrete. Personally I think the driver tried to get the forms to blow out, he was mad that we did not use a pump. Dang system works real well.
I looked at a number of other ICF systems but the Quadlock was the only one that can change thickness of concrete and or thickness of foam at will in the middle or in a corner of a wall. And with 5' walls it does not need additional bracing. It cost a bit more than the other foam systems but the freedom of design and no chance of a blowout were important to me.

 

[stee6043]

I think you're going to end up with a very interesting case study here. Is bigger always better? I sure hope you can get to the point where you can effectively run several days between fires with your system. The ROI of a tank this large has to be length of time between fires, right? Keep us updated as you continue to tweak....

 

[Justburnit]

I think you’re going to end up with a very interesting case study here. Is bigger always better? I sure hope you can get to the point where you can effectively run several days between fires with your system. The ROI of a tank this large has to be length of time between fires, right?

Yes this is both a goal and a question of mine as well as others. At this point I like the idea of a 1000 gal pressure tank, but that is not what I have.

What I do have is a mix of what some have thoughts of building as well as what others never wanted to build.

This summers goal will be to get the boiler to make usable heat from startup and to get the efficiency up into the ballpark of what Tarm advertised it to be. It is a month or so till I am done with a customer project and I can get started back on this one.

 

[Wet1]

Charlie,

Who specd the boiler as a match to that size storage? I would think your boiler is pretty undersized for that size of a tank (???), but I don't know much about the Tarms.

 

[Justburnit]

I agree the boiler is undersized. It was speced by the owner of Tarm in NH. I expected to buy a Solo 40 or even a 60. He said the 30 would be more than enough. Maybe it is. We did not have any real cold last winter to see. I think we had a half day at -15° or so but no long term to test a system by.

We will see how the changes I make to the boiler will help with performance.

 

[Wet1]

I agree the boiler is undersized. It was speced by the owner of Tarm in NH. I expected to buy a Solo 40 or even a 60. He said the 30 would be more than enough. Maybe it is. We did not have any real cold last winter to see. I think we had a half day at -15° or so but no long term to test a system by.

We will see how the changes I make to the boiler will help with performance.

Well I guess as long as the boiler is capable of meeting your heating needs, plus the losses of your tank, it's technically large enough for your system. The problem becomes how frequently it has to run and for how long... which I would image is a lot in that configuration.

I'm sure anything that improves efficiency will be a significant improvement. But I'll be surprised if your mods will be enough to get you away from frequent and/or long burns. You might want to think about selling your 30 and going with something larger...

 

[DaveBP]

Charlie,
I've heated exclusively with wood for over 30 years here in Maine but I have NOT used a gassifier for several seasons as a lot of folks on this forum have. Everyone who has stresses that without really dry wood a Tarm (or any other brand of true gassifier wood boiler) is just a wood stove, and maybe not even as good because of condensation issues. And here in the northeast, really dry wood doesn't happen the same year it was cut, split and stacked. This forum is filled with stories of people having trouble when starting out, trouble that went away when they used wood properly dried for a long enough time. Hang in there for a different experience with bone dry fuel.
And I don't share the opinion that your tank is necessarily too big for your boiler. The idea that your boiler will take forever to heat the tank back up is based on the assumption that you let it become depleted of heat before you fire the boiler again. Fire it whenever the tank loses about as much heat as one firebox load will top back off. If that's twice a day in January, OK. In the fall and spring that might be every few days. But with that big a flywheel, you should have enough slack to be able to do it when it's convenient for you. And convenience is just as important to me as an efficient burn without idling.

 

[Justburnit]

You might want to think about selling your 30 and going with something larger

That has been something I have had on my mind since I first fired the Tarm. I do need to do allot of research before I buy though. Most of the marketing for the boilers out there really do not give much in the way of details. If I recall the boiler that I liked was not imported at the time, not sure if it is here now.
I actually bought the Tarm because they were only a few hours away. Had I known of another dealer that I recently found just an hour to the west of me with a few other brands I would have had a better chance of getting a good or at least better unit. I really do not care for the engineering in the Tarm. They concentrated their design on making a flame but totally botched making usable heat from the flame. With the leak issues at the doors and the stubbornness to get the water up to temperature it is hard to believe it is rated so well. I really wish they had not been so adamant that it will burn 10-12 hours on a load of wood. Maybe if the circulator is turned off it might.

Sorry to be critical on a name brand that many love but it is sure not what they advertised it to be. The company has admitted to some of the major design problems when you know to ask directly about the issue, such as door leaks and boiling in the front right corner.

 

[Justburnit]

Charlie,
I've heated exclusively with wood for over 30 years here in Maine but I have NOT used a gassifier for several seasons as a lot of folks on this forum have. Everyone who has stresses that without really dry wood a Tarm (or any other brand of true gassifier wood boiler) is just a wood stove, and maybe not even as good because of condensation issues. And here in the northeast, really dry wood doesn't happen the same year it was cut, split and stacked. This forum is filled with stories of people having trouble when starting out, trouble that went away when they used wood properly dried for a long enough time. Hang in there for a different experience with bone dry fuel.
And I don't share the opinion that your tank is necessarily too big for your boiler. The idea that your boiler will take forever to heat the tank back up is based on the assumption that you let it become depleted of heat before you fire the boiler again. Fire it whenever the tank loses about as much heat as one firebox load will top back off. If that's twice a day in January, OK. In the fall and spring that might be every few days. But with that big a flywheel, you should have enough slack to be able to do it when it's convenient for you. And convenience is just as important to me as an efficient burn without idling.

Yes, Ever since I started with the Tarm I realize I want a low mass boiler that just makes heat. If I am correct the Seton or Greenwood are that style. I would like a bricklined wood chamber with baffles to hold heat and a tube type transfer with a respectably long flue path.

I intend to make the add on tube type transfer for my boiler so I can change the flue path from the ½ second flow the Tarm has to closer to a 4 second flow path. Let the transfer tubes in the Tarm soot up since they are all but useless as is and let the heat get made from the firebox on the Tarm and from the low mass transfer I will build.

I was hoping to have more wood leftover from last season but that did not happen. A few cords, better than nothing. The wood I have had delivered so far this year looks good and I have many more cords coming. It may take awhile to get a few years of wood stored up.