Most insulation conversations end at wall thickness. The one number that appears on the certificate, the K coefficient, is a laboratory result. Thickness is one of the things that goes into it. Knowing how the measurement is set up is what makes a supplier's figure something you can question.
The rig runs in the opposite direction
The roadside inspection guide published by Turkey's Ministry of Transport and Infrastructure describes the arrangement: the equipment goes into a closed test tunnel, the tunnel is set to 7.5 °C and the interior is raised to 32.5 °C with heaters. That establishes a 25-degree difference. The heating power spent holding the interior steady is measured, and the K coefficient follows from it.
Heating a body that will spend its life being cooled looks backwards at first. What matters for heat flow is not direction but the difference between the two sides and the power spent maintaining it. The watts drawn by an electric heater can be read directly; achieving the same precision on the cooling side is far harder because of the compressor cycle.
Twenty-four measuring points
The same guide puts 12 sensors inside the body and 12 outside, distributed according to the shape of the body. A single thermometer cannot see the thermal bridge at a corner, the leak around the door, or the difference between floor and ceiling. Averaging twenty-four points folds all of that into one number.
The stability conditions are stricter than the number itself
| Condition | Value given in the guide |
|---|---|
| Steady-state duration | at least 12 hours |
| Temperature variation within it | no more than ±0.3 K |
| Variation over the preceding 6 hours | no more than ±1.0 K |
| The two compared measuring periods | at least 3 hours each, at least 6 hours apart |
| Difference in power between them | less than 3 per cent |
| Period used for the K calculation | 6 hours |
| Mean difference between start and end of that period | no more than 0.2 K |
| Total test duration | 2-3 days |
Those conditions serve one purpose: making sure the body has genuinely reached equilibrium at the moment of measurement. A body still warming up produces a better number than a body at equilibrium. The six-hour window and the 3 per cent rule exist to close that gap.
The same measurement logic settles the question of refrigerated vehicle or insulated container: the comparison is made from reports, not from claims.
The result belongs to a type, not to one vehicle. The test report is issued to a manufacturer and to a type. Under Article 11 of Turkey's regulation on special equipment for the carriage of perishable foodstuffs, the type test is repeated on one reference unit for every batch of 250 units of the same type. If production passes 250 units within two years, the test is repeated at the end of the two years; if 250 units are not reached within six years, it is repeated anyway. For refrigerating and heating units the report is valid six years from approval.
The letter code comes out of this measurement. The thresholds in the guide are plain: normal insulation is 0.4 < K ≤ 0.7 W/m²K, heavy insulation is K ≤ 0.4 W/m²K. Heavy insulation additionally requires a side wall of at least 45 mm on equipment wider than 2.50 m. The second letter of a code such as FRC or IR is a direct read-out of this measurement.
Questions that come up
Who runs this test in Turkey?
According to the guide, TSE is authorised by the Ministry of Transport and Infrastructure for approval, certification, periodic inspection and testing under ATP. Three type test stations were set up for Turkish bodybuilders and nine periodic test centres nationwide for equipment in service. The first national ATP certificate was issued after 15 May 2017, and more than three thousand certificates had been issued by the time the guide was written.
Is a test done in one country valid in another?
The guide states it directly: parties to ATP are deemed to accept the work of one another's test centres, and a test result obtained in one country is valid in every other ATP country.
The container side
The regulation lists special transport equipment as vehicle bodies, containers and insulated transport containers, so a container falls inside the definition. Being inside the definition does not mean the model in front of you has been tested. The useful question is whether a report exists for that type, and what its number is.
