But how is the steel coil arranged? on shelving units, palletized, pictures, etc would help. As far as mounting, is the ceiling 15m or is the ceiling taller with pendant mounts down to 15m?
If you assume a coverage radius of approx 30m (again this HIGHLY depends on the edge environment along the permiter as to whether you need two rows of APs or a staggered midline, etc), using a downfiring 90deg directional antenna, you would need a minimum of 8 APs without much overlap. 50% overlap would be 12 APs, 100% overlap for full redundancy would be 16 APs. Then you have to look at client type, but with downfiring directional antennas like the ANT-35A.
Also, it's VERY important to note that at 15m the AP-367 is likely a much better alternative. It's less expensive, no need to external connectorized antennas, and the mounting solutions are more cost effective (since you don't need the ADP to use outdoor metal mounting assets on the 228). You may end up needing a few more AP-367s, but the lower overall cost and the much more redueced installation times will more than make up for it.
To compare, if you go with a 228, you need:
1 x AP-228
2 x ANT-35A
2 x AP-ANT-MNT-3
1 x AP-270-MNT-ADP
1 x AP-270-MNT-H2 (or H1 if you need adjustment)
If you go with an AP-367, you need:
1 x AP-367
1 x AP-270-MNT-H2 (or H1 if you need adjustment)
The overall cost of the 367 solution is much much more attractive.