can a person just run a 25' coil of copper or does it have to be a straight line pipe.
I think the manufacturer's have the 25' to 50' guideline when installed in ambient shop air situations. I have seen this installed in a manifold type of arrangement, up and down, repeatedly, to accomodate the 25 to 50 length in a shorter wall span. Realize here that each drop would need a drain.
Any time you can introduce a cooling mechanism, whether it is a coil of copper in a bucket of water, a heat exchanger/cooler, or a dryer system, you have now replaced the pipe length requirement with a device to perform the same function, likely more effectively. I have even heard of a copper coil passed through the shop refrigerator to cool the air and condense any vapor. (use caution with this not to drill through freon lines)
Other air system layout practices tend to fall under "common sense". Where the TP tools link shows some good theory, one of them still can be improved upon. One version shows a perimeter system in a loop, with all the "drops" that go up before dropping to the air outlet, using a separate drain. Where the other version shows more of a straight run, with any and all moisture dropping to the air outlets, requiring a moisture trap at each outlet. By simply using a 1" drop every 10' run in your system layout (to promote drainage to the end) and using the "all outlets go up before dropping", you will promote draining any moisture to the end of the line and not the outlets, as gravity works to keep it from the outlets. Following this scenario, you can use one drain at the end of the run instead at each outlet. Here's a link that shows my system for some examples of these..
http://www.garagejournal.com/forum/showpost.php?p=2100537&postcount=57
