During 2007, my research and efforts focused on making sure that the HG 3a device was CAPABLE of producing the 45,000 Btu/hr that a reasonably well-built, medium-sized house in a cold climate is likely to need for complete heating on the coldest day. That was clearly confirmed and the HG 3a unit was experimentally measured to be able to produce around double that at around 90,000 Btu/hr.
During much of 2008, research and efforts have been more focused on enabling the HG 3a device to produce LESS heat, for the MILDER months. This is technically not necessary, as excess heat could be easily dumped to outdoors! But that would be wasteful of the heat in the materially carried in to the unit, noting that around five to seven tons of material need to be carried and loaded into the unit during a complete winter, and the idea of having to carry MORE than that seems unattractive! Therefore, modes of operation where smaller amounts of heat are CREATED seem very attractive for such mild-weather operation.
It became clear that THICKER pieces of organic materials were desirable during mild weather. Wood chips and tree bark seem useful in very mild weather. Straw, most kinds of cardboard, newspapers, seem suitable for somewhat cooler weather. The very thinnest pieces of material, such as fine lawn grass cuttings and tree leaves, seem better to save until the coldest weather, for greatest heat production and output.
These differences have other effects. When BALES of straw or hay are used, I have generally just separated the bales into 1/3 sections to fit through the feed door of the HG 3a unit. I have discovered that those chunks tend to stay together! This causes far greater difficulty in rotating the unit, as many heavy chunks of those bales tend to stick together, until they eventually tumble across and down! For this, the small motor we used to rotate the unit had problems!
When thick materials such as straw or wood chips are used EXCLUSIVELY, the effect of slowing down heat production is accomplished, for mild weather heating needs. However, the interior of the HG 3a unit seems to tend to then operate at lower temperatures. If ONLY really thick pieces of material are used, such as tree bark and thin branches, it seems to often operate at around 90ºF to 100ºF temperature. If ONLY wood chips and straw are used, it often seems to operate at around 105ºF to 115ºF temperature. This seems to then have the additional effect of slowing down the processing due to the fact that ONLY the mesophilic bacteria can then prosper. They tend to process the material fairly slowly and they cannot digest many of the more complex organic molecules. For now, our recommendation is to NOT allow the system to EVER get above about 125ºF during mild weather, because the higher temperatures then allow the far more efficient thermophilic bacteria to rapidly multiply and take over. They rather suddenly increase the heat production of the system by a factor of many times! That might be too much heat for mild-temperature needs, and it also will cause the materials to be decomposed far faster.
Some experience is indicating that loading the HG 3a unit with mostly straw and wood chips causes the unit to operate at a fairly consistent 105ºF to 115ºF, and to be able to therefore provide the very minimal heating needs for a full house for much of the entire month of September (near Chicago).
My solution to this is to TRY to monitor the mixture of materials inside, and to generally be adding moderate amounts of lawn grass regularly, to try to keep the mixture similar to what I had initially put in.
Once the system gets into the thermophilic bacteria mode (over 125ºF) those thicker materials seem to also start decomposing much more rapidly, but never remotely as fast as the cut grass disappears.
If the corn is GROUND, which then breaks apart the shells and exposes the inside of the kernels, the decomposition all goes very rapidly, about as we had initially expected. We are not sure it is worth the time, trouble and expense to grind feed corn to use it in this way.
As to finding such a leak, we currently do not have any good plan, except to wait until after the heating season and examining the interior with a bright light after having emptied the unit, and then using a patch from a waterbed repair kit. As a result of this, we are generally running that unit with somewhat less water inside it, without the five-gallon constant puddle that we think is desirable in the bottom of the chamber. Our initial concept is that by having such a puddle there, then ALL the organic material is able to get soaked for a couple minutes every half hour or so, so the thermophilic bacteria will have their ideal conditions at all times and for all the material inside the chamber, temp above 125ºF, immediate access to moisture, and immediate access to oxygen from the air.
We are operating one HG 3a device inside the living space of a house and WITHOUT sending the processed gases outdoors through a vent pipe. Our intention is to see if any smells are ever created, and whether such smells might be used as a clue to turn on the blower to provide more oxygen (under the assumption that such smells would only be formed if some anaerobic decomposition has occurred). In general, it creates a somewhat musty smell that resembles the smell of woodburning but to less extent.
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C Johnson, Physicist, Physics Degree from Univ of Chicago