The chicken coop has two 4”-diameter air vents. Each vent has an inline duct fan capable of moving air at 100 cubic feet per minute. They are arranged so one fan pulls air into the coop and one fan pushes air out. The volume of the bird quarters is a bit under 900 cubic feet. So, the birds get a complete air change every 9 minutes, or so.
In the previous versions of the biomeiler, heat was extracted from the pile by a ventilation pipe coiled through the pile. Outdoor air was drawn through 100 feet of 4”-diameter corrugated drain pipe. The heat from the composting material warmed the air in the pipe as the fan drew it into the coop. I will continue to do that with the current version of the biomeiler. Additionally, heat will be extracted by water flowing through the PEX pipe wrapped around the inner and outer cores.
It took some thinking to come up with a good way to get the PEX pipe out of the pile and into the coop without too much extra complication. I did not want to make any new wall penetrations and I did not want to buy a lot of extra insulation to keep the water from freezing. What I decided to do was cover the PEX pipe with foam pipe insulation, attach them to the ventilation pipe, and insulate the whole collection together.
I added thermocouples to measure the temperatures of the water in the pipes as it enters the inner core on it way from the coop and as it exits the outer core on its way back to the coop. That direction of water flow was chosen because heat transfer is maximized when the temperature difference is maximized and the inner core is likely to be warmer than the outer core.
Insulating the pipes was another wrestling match. It was even colder today than when I wrapped the coils around the cores. Also, the duct tape did not want to stick in the cold. I had to hold the ends together and warm it with my hands to get it to work. Finally, though, all the pipes were bound, fiberglass insulation was wrapped around the bundle, and the plastic sleeve material was slipped over it all.
