I'm kind of reluctant to use the term "geo thermal" because it tends to invoke a more involved system like you're saying with exchangers and such. The system I saw on this TV show was simply air in / air out. Maybe this worked better for this person because of where they were located (they definitely were not out in the middle of the desert)... but it seemed like it would provide a solid temperature year-round, cooler for sure, even if not perfect.
Don't think geothermal works very well with air directly, they normally use liquid and heat exchangers. And you might need 1000s (maybe 10s of 1000s...) of feet of pipe with liquid buried pretty deep in the desert to support the # of miners you can pack into a 900 sq ft shack.