Freezing Technology

6.1.2 Insulation

The choice of insulation is very important as it accounts for a large proportion of the total construction cost. The insulation material and thickness is also important from an energy point of view. Besides a satisfactory thermal conductivity coefficient the insulation material should also be odour-free, anti-rot, vermin and fire-resistant and impermeable to water vapour.

Typical insulation thickness for chill and cold stores utilizing different insulation materials

Insulation	Calculated thermal conductivity (kcal/m hoC	Thickness (mm)
Polystyrene	0.033	220
Styrofoam FR	0.030	200
Polyurethane	0.025	170

Vapour Barriers

 Water vapour in the air gives rise to a pressure and together with the other gases present. The partial pressure exerted by the water vapour is proportional to the quantity of vapour present and the vapour in the air will tend to migrate from areas of high partial pressure to areas of low partial pressure. Hence, there is a tendency for moisture in the ambient air to pass through the insulation of a cold store to the area of low partial pressure within. When this vapour is cooled, it condenses and the build-up of ice will eventually affect the insulation properties of the cold store wall and also weaken the structure of the wall or building.  

Foundations and Frost Heave

Low temperature stores built directly on the ground may require special precautions to prevent the build-up of ice below the cold store floor. The ice formation causes distortion known as “frost heave” (fig.) and in particularly bad cases, it can lead to the complete destruction of the structure of the building. The conditions that give rise to frost heave are rather complex, since they are related to the type and texture of the soil, the insulation properties, the availability of moisture, the dimensions of the store, seasonal climatic variations and other factors. Two methods of preventing frost heave are commonly used. The ground below the store can be heated either by a low voltage electrical mat in the cold store foundation or by circulating a heated liquid such as glycol through a pipe grid built into the foundation. The heat for the glycol is usually obtained from the compressor hot gas through a heat exchanger.