The refrigeration capacity of ice:
Melting one kilogram of ice at 0°C creates 80 kcal of refrigeration capacity; heating water by 1°C produces 1 kcal, and heating ice by 1°C produces 1/2 kcal.
Consequently the main refrigeration capacity of ice is at melting point; the temperature of the ice has virtually no effect of the overall refrigeration capacity.
Energy requirements for ice production:
The energy, which is used later in the form of refrigeration capacity, initially has to be used to produce the ice. For sub-cooled ice (ice below 0°C) an over-proportional amount of energy has to be used, as the ice itself has an insulating effect, which has to be overcome in order to sub-cool it.
Ideal ice temperature:
The optimal temperature with regards to energy is therefore just below freezing at -0.5°C. The full refrigeration capacity of the ice lies here, without excessive amounts of energy having to be applied to produce the ice.
Ice is always exposed to a certain amount of air humidity and always emits moisture by melting. When this moisture re-freezes, the ice sticks together.
The colder the ice is, the easier it is for the moisture to freeze. If defrosted water arises on the surface of an iceberg in a reservoir, then this water flows down the ice and freezes on the pieces of ice, it passes = the pieces freeze together. This effect becomes stronger, the longer the ice remains and the more moisture there is.
As a result, for example flake ice at -7°C tends to freeze together into lumps after a few hours; this can be delayed by storing the ice in a room chilled to around -5°C.
Chip ice at -0.5°C has the characteristic that the moisture does not re-freeze, as the temperature difference between the ice and the moisture is too low. As a result chip ice can be stored for days at temperatures above 0°C (ideally up to 4° to keep defrosting to a minimum), without freezing together. A light frozen layer merely forms on the surface, while underneath the ice remains loose and granular.
When calculating the storage volume the bulk weight is important:
1.00 t / m3 for water
0.92 t / m3 for BlockIce
0.50 t / m3 for ChipIce or FlakeIce
That means that when storing 1,000 kg of chip ice, a storage area of 2 m³ plus a reserve for the inverted cone = approx. 2.5 - 3 m³ is required.
The greater the surface of the ice in relation to its volume, the faster the ice melts. i.e.:
• micro ice (with small chip ice particles) melts faster than macro ice (large chip ice particles)
• scale ice (ice thickness of approx. 2 mm) melts faster than macro ice (ice thickness 9.5 mm)
If fast melting = rapid cooling is necessary, then micro ice (or StreamIce®) should be used.
If long durability (e.g. for transporting fish in warm conditions) is desired, then macro ice should be used.