For cooling without freezing, Q = mass × specific heat × temperature drop / cooling time.
In short: freezing also needs latent heat and cooling below the product's freezing point.
Use product-specific data and include packaging where significant. Produce may add respiration heat. A storage room is not automatically a blast chiller.
The formula
Q_product = (m × c × ΔT) / (t × 3 600)
- m = mass loaded per day (kg)
- c = specific heat of the product above freezing (kJ/kg·K)
- ΔT = temperature drop required (K)
- t = available cooling time (hours); dividing by (t × 3 600) gives the result in kilowatts (kW) — multiply by 1 000 for watts (c is in kJ/kg·K)
Specific heat values
| Product | Specific heat c (kJ/kg·K) |
|---|---|
| Fresh meat | 3.2 |
| Fish | 3.6 |
| Dairy | 3.9 |
| Fruit and vegetables | 3.8–4.0 |
Freezing products need latent heat
Freezing products? If the goods cross 0 °C, the formula above covers only the sensible heat above freezing. You must add the latent heat of fusion (the energy to turn the water in the product to ice, roughly 250–335 kJ/kg) plus the sensible heat below freezing. A simple m × c calculation badly under-sizes a freezing or blast-chilling duty — treat those as a separate, larger calculation.
Respiration load for produce
Fruit and vegetables also keep generating heat after harvest (respiration load); for large produce stores, add this from published crop data. It is small for a few pallets but significant for a full produce warehouse.
Related articles
- Heat Load Calculation: The Four Components
- Infiltration load explained
- Internal heat sources
- From total load to design load
- Using the Frostbox size calculator
For a checked calculation, use the Frostbox size calculator or contact [email protected].
