Reefer Pre-Cooling Time Calculator

Estimate time to a cooling target by fitting a constant-asymptote exponential curve to readings or a known half-cooling time. Use measurements from the same location under steady conditions. Air readings and product-core readings describe different temperatures; the fit is not a validated cooling procedure.

How to use this tool

1. Choose what you know: one reading plus the supply-air temperature, three readings taken at equal intervals, or a half-cooling time.
2. Enter the starting temperature and the target temperature.
3. Enter the time to your reading and the reading itself (or both readings).
4. Read the time to target and check the predicted temperatures in the table.

Formula

T(t) = Ta + (T₀ − Ta) × e^(−k t), time to target = ln((T₀ − Ta) ÷ (Tt − Ta)) ÷ k

Ta is the cooling air temperature, T₀ the starting temperature and Tt the target. The half-cooling time is ln 2 ÷ k: in each half-cooling time half of the remaining difference is removed, so three of them give the "seven-eighths cool" point used in postharvest cooling. With three readings T₀, T₁, T₂ taken Δt apart, the temperature being approached is (T₀T₂ − T₁²) ÷ (T₀ + T₂ − 2T₁) and k = −ln((T₁ − T₂) ÷ (T₀ − T₁)) ÷ Δt.

Example

Product loaded at 25 °C with 1 °C supply air reads 13 °C after one hour. Half of the 24-degree gap is gone, so the half-cooling time is 1 hour. Reaching 4 °C means only 3 of the 24 degrees remain, one eighth, which takes three half-cooling times: 3 hours.