Chris McClellan

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since Oct 24, 2013
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Recent posts by Chris McClellan

I'm so excited to see the experiment under way, and so beautifully detailed. How is the dust? If you are getting dusting I get good results painting cob and wood and limewash with a coat of clear home made milk paint. It just gives a little gloss and kills the dust. I was able to visit a "Soddie" last year which was our Prairie ancestors' version of the Wofati. They used limewash to brighten and seal the interior as well.  Above beds and cooking surfaces they plastered with newspapers or cloth or whatever they could get to keep the dirt from settling on them. A "canopy" bed with insulating curtains was pretty normal before central heating too.
2 weeks ago
if you are experiencing any dusting on your beautiful interior lime walls you can seal them with clear or tinted milk paint. fresh lime will dust less than stuff that has been sitting in a bag for a while so just put another layer on when you feel it is fading. I am watching your adventure with great interest.
3 weeks ago
I suspect it would work well while it is really cold out until the mass started to warm up. I've wanted to try one with a horizontal exhaust at the lowest point and a chimney on an up-down tee on the end to let overly cold gasses just fall out and give a little draw when the gasses get warmer after it has been running a while. I'm not sure the heat riser I built here has enough thrust to push the gasses all the way through without the help of the heated final chimney. Kirk Mobert actually built one one time that ran the chimney down hill to cause thrust by taking all o the heat out of the exhaust. He said it worked great until it heated up.
2 months ago
For a house that will not get into the negative digits I would suggest running your exhaust through the floor to warm the floor. The only time I have had trouble with this was when I did it in a tiny house that didn't have an insulated floor and it worked well most of the time but when it got really cold out and no one had been there to feed the fire for a few days the floor mass took all the heat out of the exhaust instead of just most of it so the fire burned fine for about 20 minutes then vapor-locked when the pressure from the "cold plug" of super cooled 40 degree F exhaust steam was too cold and heavy for the chimney to lift it out of the floor even though the heat riser was pushing with all its might. In cold climates especially you can have too much mass. I love when I can get warm feet without the hassle of heating and distributing water.
2 months ago

Cleaning the paint off your barrels so they don't offgas into the house and make you sick is an important part of building a Rocket Mass Heater. We've done it with a sand blaster (long and messy). We've paid a barrel refurbisher to do it (very nice job but expensive at up to $40 per barrel). We've thrown them in a bonfire (inefficient and dirty but fun, just don't breathe and don't roast marshmallows). We've used an extra lid for the drum we are trying to burn off to make a more efficient "pocket rocket" heater. That works but it doesn't burn all of the paint off evenly. Unless you wrap the barrel in newspaper soaked in clay slip the paint just goes directly into the air, and the basic pocketrocket it doesn't help getting the paint off a drum lid (we use them in some of our designs).

Enter the "overage barrel". These are special 60 and 80 gallon barrels one of my suppliers sometimes gets that are used to contain a leaking 50 gallon barrel without opening it to pour its contents into another barrel. So take one of these big barrels and make a pocketrocket out of it. Put three bricks at the bottom to hold your 50 gallon drum. If you want to burn off a lid you can put the lid on top of the bricks, then add three more bricks, then put in your barrel. Size the feed tube length so it sits a couple inches from the bottom of the inside barrel. Add fuel and go. We are finding that the big pocketrocket approach burns the paint off much faster, with less fuel because the outside barrel holds the heat in. The paint fumes also appear to burn up in the hotter environment.
2 months ago
Fantastic work Josiah. What was the source of the brown glass? I suspect the darker glass absorbed more solar energy as anything darker tends to, but different types of glass also melt at different temperatures. Heck even different sizes of chunks melt at significantly different temperatures. Sand sized glass bits apparently insulate themselves from the sun and don't melt as well as bigger chunks. The formula I found from folks who do this all the time that worked with the rocket glass melter was bring it up above 1600 degrees for half an hour plus so it will melt uniformly, then let it cool down very slowly (anneal) so the glass cools evenly and doesn't crack along temperature fault lines. For anything over 1/8" thick this process takes at least 6 hours according to what I've read and according to what I got to work with a rocket heater.

I've attached here a firing graph from a glass industry paper showing how long to keep the glass at what temperature in order to have it fire properly. The attached pdf is the entire document in case anyone wants more technical data.

I wish I had found this before I started putting any time into the first version of the solar melter from the ATC that only melted a 1/4" circle of glass. Josiah did a lot better, but it also kept cracking. I think the details in this industry paper point the direction needed to get a better result next time, both in telling us what temps we need for how long and telling us how fine our control of our machine needs to be in order to have it work for thicker and larger panels. Reliably getting a properly annealed tile of glass much bigger than a quarter I think is really a stretch for this approach, but not impossible. Below are my takeaways. I invite comment on this list, especially from Josiah and any other folks following this thread who actually melt glass on a regular basis.

The cracking of the cooling glass that we observed (both in my version and Josiah's version) are consistent with the industry technical statements that the glass needs to be uniformly and consistently heated over its entire surface and down through its entire body throughout the entire process, not spot heated, and not heated by a moving spot.

Our current lens focuses enough energy to produce a 1/4" spot of 2000 degree Fahrenheit according to specs. That is sufficient to provide the 1600 degrees necessary to melt that spot about 1/8" deep.

If we unfocus the beam to uniformly cover a 2"x2" tile we are applying the energy at 1/16th its original concentration, which is not enough to melt the 2x2 tile.

Josiah's insulated chamber improves performance, but not 16 times as much. Maybe 4x based on reliably producing quarter-sized medallions that didn't crack. Josiah did the reflector help?

A glass lid of any sort appears to impede solar gain more than it helps by trapping residual heat. Further conversations with glass experts and Josiah's tests have convinced me that even the cleanest uncoated glass of any sort absorbs or reflects too much energy. Someone else may find a better glass for this, but even common window glass which is 99.99something optically pure provides too much impedance.

A bigger fresnel lens (say a free one with 4x the surface area from a bigger donor TV) I think would take us from iffy melty to consistently melty temps on a 2x2 tile, maybe even bigger.

Adding thermal mass within the insulated envelope could help but only if our lens is big enough to focus enough BTUs to melt the glass uniformly AND heat the thermal mass all at once. Without a lot more BTUs I think additional mass only keeps the glass too cool to uniformly melt. We also don't gain anything from attempting to preheat additional mass (with solar) since the firing takes most of a solar day.

Automated tracking should make a significant difference in giving us the longer exposure to high temperatures we need to melt the glass completely and uniformly and give it the many hours of BTU input it needs to anneal. 6 hours plus at 900 degrees plus throughout its body for anything more than 1/8" thick is what the book says.

3 months ago
Jon unless you are firing your own clay pots to put your home grown food into you are going to need some kind of container. Glass is better than plastic for a lot of things. I like the idea of minimizing consumption, but I find it often challenging. I am excited by this idea not because I think it is practical or that I think it will work how we are hoping it will work, but because we need to unnormalize the casual use of energy intensive materials and processes and really good way to do that is to understand the scale of our casual industrial use by comparing it to what we can gather naturally (like from the sun) with home made apparatus and scaling down much of our use to fit what we know we can produce nontoxicly while we learn to make better apparatus
3 months ago
Lawrence, it shipped Monday via media mail. thanks.
3 months ago