The graph shows the temperature in the chicken coop, the temperature of the air in the vent pipe coming from the biomeiler, and the temperature of the outdoor air. The electrical energy usage would be shown for any days when the electric heater was used, but it was not needed this month.
All month long, the biomeiler kept the air entering the coop within the desired winter temperature range of 45 +/- 10F. The body heat from the birds further warmed the coop and kept the temperature above 60F for the entire month.
When the temperatures are in the 60-70F range, the coop is pleasantly warm and dry. However, when the temperature rises above 70F, the coop becomes quite humid until the litter dries out. That is the current situation. When I enter for chores, my glasses steam up and I try not to think about what I may inhale.
We try to move the birds to their outdoor pens before the coop gets to the 80s. Often, as is currently the case, the outdoor conditions are not appropriate for moving the birds. So, we open the window, prop the door partially open, and hope the local predators are unobservant. This year, we may not face that problem.
Amazingly, even though the outdoor temperatures are in the 50s and 60s, the biomeiler is cooling the incoming air to 37F! You probably find it strange to hear of a compost pile steadily absorbing heat, yet remaining cooler than the environment. Indeed, I must admit to feeling some puzzlement when I discovered the situation.
My first thought was that the reference junction was malfunctioning and biasing the thermocouple readings to be too low. Some double-checking eliminated that possibility. Next, I reasoned that only a material undergoing a phase change could absorb so much heat without increasing in temperature.
During the winter, it was often the case that the trend of the biomeiler temperatures was opposite to that of the outdoor temperature. Another observation was that the temperature in the vent pipe was steady at about 42F, almost regardless of the outdoor temperature. I speculated then that the moisture in the mantle of the pile was freezing and latent heat was being released to the vent pipe and the core layers. This morning, I did some exploratory digging in the surface of the biomeiler and uncovered the evidence necessary to confirm my suspicions.
About 6” beneath the surface of the pile there lies a large body of ice. The limited probings I made indicate that the ice layer is about 4’ in radius and has a thickness of about 6” at the outer edge.
In one area, I dug deeply enough to reach the upper coil of the vent pipe. The pipe had a surface temperature of 35F and the compost surrounding it, thoroughly soaked with meltwater from the ice above, measured 33F.
This discovery has significant positive implications for the future use of the biomeiler. It has already proven itself to be an affordable and dependable source of low-grade heat, and now may also be equally affordable and dependable as a provider of air conditioning!
These thoughts will be further developed in part 2 of the April update, which will more-specifically address the biomeiler’s internal functioning.
