How should hold time be read?

A: Ask for the starting differential and payload; an empty-case figure drops to a third when loaded.

How is panel count set?

A: Heat load over latent heat, then the supplier's table, then one measured run.

Why does empty weight matter?

A: Loaded with panels, passive cases often pass twenty kilograms and need two people or castors.

Is the battery sized on peak power?

A: No: average draw times hours plus twenty percent; the peak lasts a moment.

What does acceptance cover?

A: Loaded hold, empty weight, recovery after three openings, battery run-down. ---

Choosing a Temperature-Controlled Case: Range, Hold Time, Power

Quick answer: Three hard figures decide a temperature-controlled case: the target range, how long it holds after power is cut, and how much power it draws. Hold time is the one usually fudged — twenty-four hours means little without the starting differential and the payload.

Three hard figures
Range and phase-change material
Hold time: three conditions, all required
Power and supply
Acceptance: four measurements
FAQ

1. Three hard figures

Target range comes first, written with both limits — two to eight degrees, or minus twenty to minus ten. A qualitative word like chilled cannot be accepted, and the range decides which phase-change material applies.

Close-up of the lid gasket and insulation lip

Hold time is the drift from the starting value to the upper limit with no power and no opening. It is bound to three conditions: starting differential, payload and ambient temperature. Quoted alone, it means nothing.

Power is the draw needed to hold temperature in an active case. Passive cases have no such figure, but the energy to precondition the panels is the same account kept in a different table, and putting all three on one sheet shows the difference faster than comparing ranges.

Figure	How to set it	Conditions required	If short
Range	both limits stated	ambient range	nothing to accept against
Hold time	drift to the limit, no power	differential and payload	half of what was promised
Power	average draw to hold	ambient and opening rate	battery undersized
Empty weight	case with panels	panels included	too heavy to carry

2. Range and phase-change material

The range follows the phase-change point, not wall thickness: cold chain at two to eight degrees uses a material near five degrees, frozen work at minus twenty needs another. Mixing them puts the temperature outside the band while the case looks fine.

The case open showing insulated walls and a cavity with phase-change panels

Panel count comes from heat load divided by latent heat, where the load includes payload heat capacity, wall leakage and air exchange on opening. Use the supplier's table, then verify with one measured run; sizing panels by volume is the usual cause of excursions.

3. Hold time: three conditions, all required

Measure hold time with a rated payload, precooled to the lower limit, at the highest ambient, recording hourly until the limit is crossed. The test takes eight to twenty-four hours and has no substitute.

Close-up of the temperature logger pocket inside the lid

The usual claim quotes an empty case with a twenty-degree differential. Loaded, the heat load rises three to fivefold and hold time drops to a third. Require the figure at rated payload and maximum differential, and put it in the contract.

4. Power and supply

Active cases are sized on average draw, not peak: the peak lasts a moment, while capacity comes from average draw times hours in transit plus twenty percent.

Two cases on a pallet with a data logger beside them

Three supplies exist: vehicle power, internal battery and mains. Long hauls usually combine battery with vehicle charging; battery-only sizing follows the longest outage, not total transit time.

5. Acceptance: four measurements

Four measurements: loaded hold test with the crossing time, empty weight including panels, recovery after three openings, and a battery run-down. The first two finish in one session, the others take half a day each.

Recovery after openings is the one usually skipped. Real use opens the case several times a day, and air exchange is consistently underestimated; after measuring, panel count or opening discipline usually changes.

The three figures constrain each other: a tighter band shortens hold time, and a larger payload raises draw. No selection optimises all three, so fix the one that cannot be compromised and balance the other two with panel count and preconditioning time.

Conclusion

Three items: range follows the phase-change point, hold time follows its conditions, power follows the average. Figures without conditions are paper numbers, so write the conditions into the contract and acceptance has something to measure against.

This article covers container-side specifications and design implications only, not the handling, loading or use of the contents.