First, given your location, all fans will do is relocate outside moisture t o the inside, and push inside moisture to the outside. What you need is an effective dehumidifier - which is heat/cool neutral, but does remove moistu re - albeit at a cost (electricity).
Second, based on venting to the south, drawing in from the north, you are d oing exactly the opposite of what you should do for your purpose, at least in the northern hemisphere. You want to draw air from the warm(est) side of the house, which will be the sunward side, even in Seattle. And you want t o vent to the cool(est) side, which will be to the north (no direct sunligh t).
Short of deliquescent materials, there is no passive means to remove humidi ty. Any anyone that suggests otherwise is telling porkies. Some other point s:
a) Concrete and stone (typical foundation materials) are, emphatically, not vapor barriers, so unless an effective vapor barrier was installed on the
*outside* face of the foundation walls, and beneath the concrete slab, you will have a constant source of moisture at all times, weather notwithstandi ng.
b) I really hope that you are not intending to do any sort of work involvin g electronics or you handling electrified equipment in that space. Working over a concrete floor over dirt is, essentially, equivalent to standing in an inch of water. To prove the point, with a decent VOM on AC volts, one p robe to the hot side of a receptacle, the other to the floor. As your body, assuming you are otherwise healthy, is not much more than a 10,000 ohm, 1/
4 watt resistor, be careful!
c) Cellars (more than 50% below grade) or basements (50% or less below grad e) unless designed as such from the git-go are simply not meant to be used as finished, habitable space. And in your climate, even more so. And, if yo u happen to be in an older house where local stone was used in the foundati on walls, drying them out is absolutely not a good idea unless you want you r house to start settling, big time. There is a long explanation for this, but typically old foundations were built with a mud/lime mortar with very l ittle Portland Cement involved. The stuff is solid when damp, but when drie d out, it shrinks, crumbles and fails. Here in the Philadelphia region, the likes of Dr. Desert Dry and their ilk won't touch older houses for that re ason. Again, be careful!
Best of luck - fans are a waste of money if dehumdification is the specific goal. Deliquescent materials have a high first cost, and will have you ups etting your significant other as you will be baking them dry in the oven co nstantly. But, they do work. Leaving you with machines as quick, relatively efficient means to that end. Invest in the additional condensate pump so y ou are not constantly emptying the bucket.
Best of luck!
Peter Wieck Melrose Park, PA