There is nothing surprising happening with the biomeiler, which is just as it should be. No one wants an exciting heat source for their chicken coop.
The biomeiler continues to steadily cool the incoming air. The effect was diminishing, but has stabilized. The air entering the coop was at 45F at the beginning of the month, warmed to approximately 55F, then settled on 50 F by the end of July. In consequence, the coop temperature has generally been only 5-10 Fahrenheit degrees warmer than the outdoor air temperature. The data are shown in the main image of this post.
In the last week of July, the coop was occupied by only two roosters and 15 pullets. After the previous meat birds were harvested, the next flock of 30 meat bird chicks were relocated to the recently-vacated outdoor pen. I was pleased to see that by removing the body heat contributed by the meat birds, the cooling power of the biomeiler was sufficient to bring the coop temperature down to match the outdoor temperature on July 31. It was a brief triumph, but I am celebrating it, nonetheless.
The second chart 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.
The mantle and outer core of the pile warmed steadily during the first half of the month, much as one would expect. In the third week, the weather cooled and it was more breezy than usual. I think those conditions explain the flattening of the mantle temperature curve. The slight drop in the outer core temperature could be due to heat being absorbed by the inner core. In the last week of the month, the mantle cooled slightly and the outer core warmed slightly. That trend could be explained by the outer core absorbing heat from the mantle.
It is important not to give unwarranted significance to small temperature changes. During the summer, the general trend of heat flow should be from the outside toward the center. Rises and drops in the temperatures of the layers would be due to variations in the amount of heat arriving at a layer and/or the heat being absorbed by a layer deeper in the pile.
An additional caution is that my voltmeter is not capable of measurements small than 0.1 millivolts. Because I am using Type K thermocouples, that voltage places a temperature change of 4 or 5 Fahrenheit degrees at the very limit of resolution in this experiment.
The significant cost of a more sensitive voltmeter is not currently justified, but I maintain hope of being able to use a Raspberry Pi to monitor the biomeiler temperatures in the future. The temperature sensing equipment that works with it may be trustworthy at smaller voltages. Even if it isn’t, I believe the experiment would benefit from greater time resolution in the data.
Presently, data is collected whenever I feel motivated to stand by the pile with a mug of ice water, connecting and disconnecting 18 thermocouples. It is not a bad experience in the summer, but at -40F, it gives me pause to reconsider my choice of hobbies.
It is really remarkable to see the various temperatures recorded. I enjoy the charts.
Do you plan to dismantle any parts of the biomeiler in preparation for the oncoming winter season?
Mug of ice water in hand, of course, if your temperatures are competing with ours in New York State!
Presently, I plan only to add material to rebuild a conical peak on the pile.
The peak from last fall has become several depressions.
The mug of ice water is actually for a 32F reference temperature for the data collection.
It is necessary even in the deep winter.
I would have to keep my thermocouples much cleaner if I intended to drink the water later 🙂