The main chart accompanying today’s post shows the temperatures measured in the biomeiler at a height of 4’ above the ground. This height marks the boundary between the pre-existing biomeiler and the recent extension. The data were collected by a thermocouple buried in the pile at that height at the very center of the inner core, another placed halfway between the inner and outer walls of the outer core, and a third similarly placed between the inner and outer walls of the mantle. The air temperature was measured on a thermometer in the open air.
Last month, on February 24, I began using the air compressor to pump air into the bottom of the biomeiler. With only a few minutes of aeration spread over the next five days, the inner core of the biomeiler increased in temperature by 30 F degrees by the end of the month.
At the start of March, I was much more consistent about the aeration (seen in black on the main chart). Unfortunately, consistent aeration produced the opposite effect and the inner and outer cores cooled off. When the aeration was discontinued entirely, temperatures in those regions improved before slowly dropping.
The mantle of the biomeiler, which should not have been affected by the aeration, cooled to 32F and remained at that temperature for the remainder of the month. Cooling further than that would require removal of the latent heat of fusion, which would be difficult without much colder outdoor temperatures.
I continue to suspect that there is a “goldilocks” value to aeration. Too little aeration starves the aerobic bacteria population. Just enough will allow the aerobic bacteria to thrive and generate heat without harming the anaerobic population. Too much aeration harms the anaerobic bacteria population and decreases the total heat output.
Looking at the chart, I hypothesize that there was too much oxygen present between March 1st and 6th, the right amount between the 7th and 14th, and too little from the 15th through the end of the month. I will test this hypothesis in April by applying aeration for one short period and monitoring how the temperatures change afterward.
It astonishes me that the biomeiler temperatures, whether IC, MC, or OC, don’t relate more to the outdoor temperature.
I enjoy the charts.
The outer core is surrounded by the mantle and crust, which is a 3′-thick layer of sawdust and shavings, wrapped with Reflectix.
So, there is considerable insulation between the active cores and the outdoor air.