If you have paid any attention to the saga of [The_Cube], you know that up to this point I was aiming at heating the digester by circulating hot water. I have done a lot (a lot!) of work on designing a sump to hold residual water, a heater/pump to...
“Instrumentation,” as a category, includes not only what one would expect— devices that gather information about temperature and similar parameters— but as well, devices that control, such as relays that turn on the pump for the HEx (heat exchange) units, or the electric heater.
In the case of [The_Cube], the situation is made more complex by the fact that we have two instrumentation systems, one developed (the “minimalist” system), and the second a more complex work-in-process that we will describe in another post.
To understand the top square (which holds the four sides of [The_Cube] together at the top; see the top-most wood square in the image to the right), it is useful to understand the internal framework of [The_Cube].
If you've read very much about [The_Cube], one thing you know by now is that I use jigs, which are usually small and fairly simple assemblies intended to enable getting better results. Indeed, some assembly steps might be a practical impossiblity without jigs.
![Agitator for [The_Cube]](https://www.completebiogas.com/sites/completebiogas.com/files/styles/thumbnail/public/images/agitator-model_400px.png?itok=VS5bjjgN "Agitator for [The_Cube]")
Agitation, stirring the slurry that the biogas digester contains, is crucial to insuring that your digester will produce as much biogas as it can. There are two fundamental reasons for agitation:
For the idea for this jig, I am indebted to Scott Mack who attended the Builder’s Biogas Workshop in North Carolina, in June of 2019. He took a router and put a piece of plywood over the bottom, then pegged the agitator strut boards onto a dowel in the plywood. The dowel then became a pivot so he could scribe the half-circles for the agitator cups (which are pipes cut in half) in the agitator struts. (More on all that in the blog about the agitator.)
The pump/heater is the unit that (obviously) heats the digester. For this first phase of the development of [The_Cube], I have not wanted to introduce any unnecessary complications, so for the time being, I am using electricity as the energy source for heating the digester. Some time in the future, if my efforts are rewarded with sufficient success, I will be working on solar heating options. But not just yet.
To understand [The_Cube], it helps to understand that it is made from assemblies, which are in turn made from parts and other (sub-) assemblies. Given that, what is absolutely essential to understand based on that “tree-like” structure of the bits that are put together to make the digester is that each of the assemblies, sub-assemblies and parts has a unique identifying number, which we call the Structured Part Number, or SPN.
I used to call this sump the “hot water sump”, but that’s misleading, because the water in the sump is not heated per se (that is, in the sump itself); rather, it is only heated just before it is pumped through the digester and into the HEx (heat exchange) units, saving energy. So now, at least for this moment, I'm calling this assembly the “water sump”.
