When I was researching climate battery technology in greenhouses, they claimed that climate battery tubes did not get moldy since they were full of tons of tiny holes. (almost a mesh.) They said that natural harmless fungi could then out compete harmful molds, as opposed to a solid or even a perforated pipe. From my research in mold remediation, I know that harmful molds do indeed need a competition free environment.
Would this solve the earth tube problem? Buyer beware, I have never built anything like this and don't know what I am talking about.
Of course, the pipe would have to be surrounded by gravel and have a sloped drain to daylight to avoid filling up with water. Basically running air through a French drain, and pulling it out half way down.
That sounds very interesting!
I installed a 4" fan driven earth tube air intake for my shop. It keeps the shop quite cool in the summer, but has no heating effect in the winter. I used super-ferritic stainless flue pipe that my local plumbing supply house wanted to get rid of. These have very nice rubber seals, so no moisture gets into the pipe and as a result, I haven't had any moisture/mold issues.