The sandwich panel is the building block of the cold room. On the outside, 0.4–0.6 mm painted galvanised steel sheet (stainless or PVC-coated where food is in contact), in between 40–200 mm of polyurethane (PUR) or polyisocyanurate (PIR) foam. The thermal conductivity of the foam is around 0.022 W/mK; a 100 mm panel passes 0.21 W/K per 1 m². The panels lock tightly together through the tongue-and-groove joint and cam-lock (hook) system at their edges; they can be dismantled and re-erected elsewhere.
Thickness is chosen by room temperature: 60–80 mm for +5/0 °C, 100 mm for 0/−5 °C, 120–150 mm for −20 °C, 150–200 mm for −30/−40 °C. A thick panel raises the investment but lowers the heat load, and hence the cooling capacity and electricity consumption, for life. PIR foam has a better fire class than PUR (B-s1,d0 / B-s2,d0) and is preferred in large warehouses under the fire regulations.
Points to watch in installation: panels are set on a clean, level floor with U profiles top and bottom; the joints are sealed air- and vapour-tight with silicone and plastic corner profiles; under the floor panel of frozen rooms ventilation or heating is provided so that the ground does not freeze and heave the floor. The cooling load calculator takes panel thickness as an input and shows the conduction load.