I studied Earth tube heating/cooling as a way to save energy and money when remodeling our park store. 

Earth tube cooling uses the natural stable temperature of earth soil, in our case just 5 or 6 feet below the surface, to heat a building when cold and to cool it when hot.

The Great Lakes keep our water table high and the temperature of the damp earth is in the 50's most of the year.  Tests have shown that in a reasonably sized tube over 100 ft long, the temperature of the air moving through the tubes, does not warm or cool the earth around it enough to make any significant difference.  Therefore air moving through it will be heated or cooled in relation to its constant moderate temperature.

After reviewing information I found on the web, I came up with the attached design.  It incorporates a "thermal chimney" that uses hot attic air to create a natural airflow without using electricity to power fans.  The hotter it is, in theory, the better this system would cool.  It looks like due to time and lack of a source of a cheap, dependable, tube design. 

The humid warm air of summer would cool and drop its water (dehumidify) so it is important to engineer draining and sump operations as well as a way to clean and sterilize the tube to avoid mold or mildew issues.  I don't have elevation numbers for the drainage as these are initial concept drawings.

See the concept and drawings

PDF of concept and drawings

Campground proposals and innovations

CONCEPT, DESIGN AND WEB PRESENTATION PREPARED FOR MACKINAW MILL CREEK CAMPING, MACKINAW CITY, MI
BY FRANK R. ROGALA   © 2007 Mackinaw Mill Creek Camping