Can only realistically imagine it is a way of saying "plafond actif":

[from my notes] Plafond actif Active ceiling, thermo-active ceiling (sort of radiant ceiling, heated & chilled ceiling, etc.)

Literally it appears to suggest the heating panels are mounted directly beneath the roofing, implying that there is no insulation or lining (ceiling). This could well be the case in warehouses for agricultural plant, but these days in particular it would seem unlikely that they would heat the place under those conditions.