Efficient thermal insulation is an important aspect of any cold-storage facility’s floor structure, helping to maintain the correct internal temperature, as well as saving precious energy.
The reversal of usual flow of heat and moisture inside to outside through a building structure needs to be taken into account in the case of cold storage i.e. the flow of heat and relatively high moisture levels present in the sub-soil and external environment where the temperature is relatively higher, is towards the colder (low moisture content) cold store interior, via diffusion through the cold store floor and enclosure.
The thickness of the thermal insulation layer can, in many cases, exceed 200 mm, making the use of a high-strength insulating material in the floor particularly justified, ensuring continuity of insulation for the entire envelope, including the floor as well as walls and ceiling.
The manufacturing process for extruded polystyrene (XPS) produces a homogeneous, closed-cell material structure with a smooth surface skin (the extrusion skin). This offers:
- a permanently low thermal conductivity
- water and frost resistance
- high strength
- high resistance to damp diffusion
The use of high-strength XPS boards with a high insulation co-efficient low thermal conductivity enables cost-saving ground bearing and load-distributing reinforced concrete floor structures to be used.
Increased insulation thickness is achieved using multiple layers of XPS boards - Ravago recommend installing up to three staggered layers.
The thickness of the thermal insulation will vary depending upon the required internal cooling temperature and the maximum heat flow permitted for economical operation of the cooling equipment. The value of the maximum heat flow can be used to determine the target U value needed for of the cold store envelope, and thus, the necessary thickness of the thermal insulation layers including those in the floor.
Generally the sub-soil under the floor of a cold store needs to be kept warm with heating coils beneath the insulation to avoid freezing of the underlying ground.