Thanks, Mongoose. The pvc coming out of the back middle of the keezer collar has a cap on it and a cutout to direct the return air to the right corner. The fan you are asking about is blowing that return air (hopefully) down into the pvc floor with wire shelving on top.
You can't see them because they are drilled to point down somewhat, but the pvc floor has several holes drilled in it to keep air moving and hopefully reduce moisture issues.
The two soda kegs are their to help figure out spacing of things.... I just realized how filthy they are after being in the barn for a year.