I posted pics of ground tube network I plan to use to temper subzero fresh air to DIY exchanger(in Eco-build thread). Three 100' 6" sewer pipes linked together at foundation. Each run has a nylon rope thru it that can seasonally have a bleach soaked swab pulled thru for cleaning. It will only be used in winter so condensation problems should be minimal. Capped in summer. All tubing was surplus and laid in same trench that day lighted footing drains are in out hill away from foundation.
http://ecorenovator.org/forum/renova...d-started.html
