[TowerTalk] where the condensation comes from

[jimlux]

I did a bit of calculating about what might push damp air into a conduit.

I assumed that I had 30 meters (100ft) of a 2" diameter tube where there 
was a pressure difference corresponding to a 10 mi/hr wind (it's about 
1/4 lb/sq ft)

You'd get a flow of about 2 liters/second (which is surprisingly high)

In an hour, then you'd have 7200 liters.  If you had 100% humidity air 
at 68F (20C) going in, and the soil was at 50F (10C), you'd be 
condensing out about 50 grams/hour.

In reality, you probably don't have 100% humidity at 68F. But you might 
have 50% humidity at 85F, and that's about the same amount of water.