Eutectic plates do not remove the cooling energy, they carry it. A plate absorbs heat from its surroundings while it melts and keeps the inside of the box close to its melting temperature. The cold is still produced; the difference is whether it is made on the road with diesel or in the depot with electricity. The decision shows in two cost lists filled in for the same route and the same load.
GEBHARDT plates: melting point and freezing
GEBHARDT's minimum margin is 5 °C: a -21 °C plate freezes in a freezer set to -26 °C, a -3 °C plate in one set to -8 °C; the -14 and -18 °C plates are standard only in the 480 × 280 × 34 mm size. GEBHARDT requires an air gap between plates and recommends its freezing racks for that: a plate stacked on another does not freeze through, and the box gets less cold. Freezing time depends on the cooling technology and runs from 8 to 24 hours; the table of sizes and melting points is in the fleet freezer capacity article.
Unit side: 1.8 litres of diesel an hour
Carrier Transicold puts the average consumption of a semi-trailer refrigeration unit at 1.8 litres of diesel an hour: 1.9 in summer and 1.7 in winter. The figure comes from chamber tests in chilled mode at 2 °C and frozen mode at -20 °C, with door openings simulated. Carrier lists three factors that raise consumption: the set temperature, the outside air and how often the door opens.
Unit cost items: fuel (proportional to running hours), maintenance, refrigerant recharge and depreciation of the unit. Plate cost items: freezing electricity, extra load on the freezer, depreciation of plates and containers, and labour for moving and placing the plates. Both lists must be filled in with the same units and for the same trip.
Worked example: 6-hour route, 6 plates per box. Example data: one trip with 6 hours of cooling, a box holding 6 plates of 480 × 280 × 34 mm with a -21 °C melting point. These numbers are an example; enter the duration of your own route and your own plate count.
| Item | Unit (on the road) | Plates (in the depot) |
|---|---|---|
| Main input | 1.9 × 6 = 11.4 litres of diesel (summer); 1.7 × 6 = 10.2 litres (winter) | 6 plates, 24 h in a -26 °C freezer |
| Unit price | Price per litre, from the invoice | Price per kWh, from the invoice |
| Per trip | 11.4 × price per litre + share of maintenance, refrigerant and depreciation | Freezing kWh × price per kWh + extra load, depreciation and labour |
The number of plates is multiplied by the number of trips per day. Two trips a day need two sets of plates or twice the rack space in the freezer, because freezing takes 8 to 24 hours and every plate freezes again after each return.
Which side wins. Plates win under three conditions: the freezer has spare capacity to reach -26 °C, the number of daily trips fits the plate cycle, and the litres burned on the route cost more in lira than the freezing electricity per trip. On a long route with few door openings the unit side causes fewer problems; if the freezer is already full, the plate option stays on paper.
Do not add litres and kWh together. First measure the freezer's spare capacity, then count the plates, and finally convert every item to lira with the invoices of the same period and compare them per trip. If the route, the load or the number of door openings changes, redo the calculation.
