Hi Knightly

Probably not enough head height in the room, but when building rack/trolley freezers, we would fit a false ceiling.
This is basically a set of fridge panels running horizontal in frount of the cooler (like an extension of the drip tray). The cold air off the cooler is blown over the false ceiling (the racks are wheeled under the false ceiling) the air then returns through the racks bck to the cooler (small 1 foot sections of plastic curtain are hung under the false ceiling to stop the air taking a short cut back to the cooler above the racks).

This set up will make a big difference to your freezing time (provided that no short cuts are left for the air, ie gaps around and above the racks, or racks left out of the rows).

Hope this helps

Kind Regards Andy