Cast Batch Box Rocket Mass Heater using LTGS

I am currently planning to build a Cast Batch Box Rocket Mass Heater (RMH) using Low-Temperature Geopolymer Setting (LTGS).  

I've built a working J-Tube RMH out of LTGS in order to test the techniques and materials.  So far so good.  I will attach pics of all the items mentioned in this post as replies to the post.  

My primary sources of information in this endeavor are:
- this website
- Erica and Ernie Wisner's book "The Rocket Mass Heater Builder's Guide"
- Peter van den Berg's web site:  http://batchrocket.eu/en/
- the LTGS website I was using is no longer available.

The primary design components are as follows:
- 6" Chimney and overall system
- The batch box will be 7 cast parts: (Floor, Right side, Left side, Back wall which includes the front bottom portion of the heat riser, Back bottom heat riser, Front top heat riser and Back top heat riser)
- I will use 5 forms to cast the batch box and heat riser (2 are reusable)
- Bell will be 3 layers with a 1/4" steel "lid" on top.  The layers consist of 1 1/4" LTGS on the inside, 4" concrete bricks outside of that and a decorative stone veneer
- the Batch box will be raised off the floor 9"
- the Bell will be 13.5" x 13.5" x 67.4"
- the Bell ISA computes to 25.6 cu ft
- the Heat exchange will be a total of 8' long with 3 turns
- the Heat exchange ISA computes to 31.4 cu ft
- for a Total ISA of 57.0 cu ft .1 under the target ISA of 57.1 cu ft
- there is 2 3/4" clearance on each side of the heat riser inside the bell giving a 185 sq in CSA.  This gives a 6.6/1 ratio exceeding the 5.0/1 requirement.
- a 1 1/2 story class "A" chimney will be installed inside the house through the ceiling and the roof.
- approximately 5 cu ft of LTGS will be needed at a cost of about $200 total (not including the J-tube prototype)

My questions:
1 - Will the LTGS use within the bell inhibit the system "draw"?
2 - Am I missing anything else?

My J-tube Cast LTGS RMH uses the 1 - 2 - 4 structural ratio target

It was poured using a single mold.  The burn tunnel was formed with wood and wood-glue and was designed to "burn out" upon first use.

It fired and drew appropriately.

The external temperature of the 1 1/2 inch thick LTGS was around 100 degrees F

The internal temperature exceeded the 500-degree max temperature of my infrared thermometer.  So it was "Really HOT!"

Note: I did not add enough water to the LTGS mixture.  This prevented it from settling properly.  I have adjusted my LTGS recipe to correct the issue.

Here are some snaps from my Batch RMH Sketchup

Here's a pic of the form used to build the J-Tube

Thanks for sharing Steve. I really like the direction you're headed. Please keep us updated as you install and learn to run it.

15g of Rock Wool after it was run through a kitchen blender

Here is the latest and hopefully last pic of my target Batch Box Rocket Mass Heater.  My intent is to:
- build an aesthetically pleasing heater
- add value to my home
- add an alternative heat source (wood)
- utilize a renewable energy source (wood, many don't consider this in their definition of renewable but I do)
- efficiently convert the wood to heat
- efficiently distribute the heat to the entire house

Geopolymer cuts easily with a hand saw

I am exploring another Batch Box design.  It is known as the Double Shoebox Rocket (DSR).  I will be experimenting with this idea for the next few months.  It utilizes many of the same modular components as the BBR.  Therefore, if I need to revert back to the original design, I can do so with little waste.

Latest sample of LTGS

Bell

End result look

Plumbers Torch Test after 10 mins

Here are the results of the temperature testing using a geopolymer piece 7/8" thick.

The first form is poured for the DSR.  It's inside the curing box.  Temps currently 102F on a hazy 80F spring day.

This is a view of the "Internal" components.  This comprises the actual DSR and Bell.  

The next 3 forms are ready to go.  I've adjusted the allowance for shrinkage to 11% after reviewing the first poured form's results.

Left to right they are:  Batch Box side, Batch Box floor (cut in 2), Batch Box and Shoe Box roofs (cut in 2)

6 forms have been poured so far.  At this time there haven't been any visible cracks.  :)

Looks promising. What is the LTGS recipe, and how sensitive is it to local material composition?

Phil Stevens wrote:Looks promising. What is the LTGS recipe, and how sensitive is it to local material composition?

You can read all about it here.

http://donkey32.proboards.com/thread/3283/geopolymer-code-named-kansas-city?page=1&scrollTo=29144

Here's the batch box.  Next steps are to add the P-channel, cut the port in the batch box roof, cut the shoe box sides and roof to size and set it all up.

cover pic

"Dry Stacked" Double Shoebox Rocket - next steps - mix up some cob to temporarily assemble the heater for testing, weld the metal exoskeleton.  The p-tube will be trimmed to its final length once the doors have been built.  

Very babylonian or egyptian looking !

Thanks for the updates, Steve. The dry stack looks great. In the DSR design, is the upper chamber also loaded with fuel? What are the reputed advantages of this over the standard batch box?

Phil Stevens wrote:Thanks for the updates, Steve. The dry stack looks great. In the DSR design, is the upper chamber also loaded with fuel? What are the reputed advantages of this over the standard batch box?

You can read about the concept and see some videos here:

http://donkey32.proboards.com/thread/2341/different-batch-core-riser-all

Phil Stevens wrote:Thanks for the updates, Steve. The dry stack looks great. In the DSR design, is the upper chamber also loaded with fuel? What are the reputed advantages of this over the standard batch box?

From my perspective, the DSR is simpler to build with cast components over the Batch Box Rocket style.  Another huge advantage is the ability to see the "Rams Horns" or "Vortex" in the Shoe Box via a window.  It's also slightly shorter.  

DSR exoskeleton is started.  This will provide some structure to the overall heater and also provide a foundation for attaching doors.

The exoskeleton is complete.  I've added a small (5") riser on top of the top shoebox.  I understand it's not necessary.  I already had built all of the components so I went ahead.  

The Threshold has been added and the p-channel cut to size.  I've also cut a "redneck solution" door.  :)  Getting closer to the first test . . . I think.

Here's the "redneck solution" door

I fired up the DSR today with good results.  It appeared to need more air than the recommended air inlet provided.  

The "Temporary" Bell is now nearly complete.  It will be used for testing the air flow through the system.  Once I'm satisfied that everything is working properly, I will move the DSR into my house and construct the permanent Bell.

That's quite clever!

My plan for the "Permanent Bell" is as follows:
-  External Layer is made from 4" x 8" x 16" Cement Blocks
-  Trowel onto that a layer of thinset with "ridges"  - see pic of test block below
-  Trowel over the top of that layer a layer of Geo-polymer (GP)

The test block pictured below shows 3 different "ridge" depths.  Once the sample dries, I will mix up some GP to trowel over the thinset.  My thinking is that the thinset will provide structure and help the GP to adhere to the concrete blocks.  The GP will also provide a heat shield to the concrete blocks.

From left to right is a sample of 1/2", 1/4" and 1/8" ridges.  

Your cement block, hollow or filled?

Satamax Antone wrote:Your cement block, hollow or filled?

The blocks are hollow but I could fill them with rock or sand.

Fill with concrete. Sand insulates.