Specific heat
Also known as: specific heat capacity, cp
Short definitionThe coefficient that gives the heat to be removed to cool one kilogram of a substance by one degree (kJ/kg·K). Water, at 4.19, has one of the highest values; for ice it is about half that, 2.1.
The first question in a product load calculation is how many kilos enter the room each day and at what temperature. The heat to be removed is the mass multiplied by the temperature drop and the specific heat. Watery produce needs more energy: the coefficient is 4.0 kJ/kg·K for cucumber but 2.5–3.0 for fatty meat. In frozen product the water has turned to ice, so the coefficient is roughly halved; freezer room calculations use the below-freezing value.
Cooling 800 kg of lean meat by 20 K at 3.4 kJ/kg·K means 54,400 kJ, about 15 kWh of heat. If the goods may take 10 hours to cool, 1.5 kW is enough; if 3 hours is wanted, 5 kW is needed. That is why a blast room asks for stronger equipment than a storage room. Count the crates, pallets and trolleys as well; in a load packed in wooden crates the packaging share can exceed a tenth of the product.