Insulated Panel Thickness and Unit Matching
Panel thickness sets the heat load; the refrigeration unit has to remove it at your ambient temperature. A mismatch in either direction costs money.
Panel thickness and cooling unit: they are one decision, not two
The refrigeration unit removes heat; the panels decide how much heat gets in. Matching them is a calculation, not a brand preference. A 100 mm panel with an undersized unit will not hold temperature in a 40 °C market. A correctly sized unit behind 50 mm walls will run at high duty for its whole life, consume more fuel and wear out early. The working rule is that the unit’s rated capacity at the required box temperature must exceed the calculated heat load by roughly 20–30 %, and the panel schedule must be chosen first, because panels cannot be upgraded later without rebuilding the body.
What the four panel thicknesses actually do
| Panel thickness | Typical thermal performance | Where it is the right choice |
|---|---|---|
| 50 mm | Lightest, lowest cost, highest heat ingress | Chilled distribution at 0 to +8 °C, short routes, mild ambient |
| 75 mm | The general-purpose specification | -18 °C frozen work in moderate climates; chilled work in hot climates |
| 100 mm | Strong margin at -18 °C in hot ambient | Frozen distribution at 35–45 °C ambient; long dwell times |
| 120 mm | Highest insulation, heaviest, most volume lost | -25 °C duty, pharmaceuticals, desert operation |
Thickness is usually not uniform: the floor and roof normally run one step thicker than the walls, because the roof takes direct solar load and the floor takes conductive gain from the road surface. A body quoted at “75 mm” that does not state the floor and roof schedule has not been fully specified.
How the heat load is calculated
Four terms dominate. Transmission through the panels, driven by surface area and the temperature difference to ambient. Solar gain, which on a white roof in direct sun can add a third to the transmission load. Product load, meaning the heat the cargo itself brings in — warm product placed in a cold box is the single largest load a frozen body ever sees. And infiltration, meaning the warm air that enters every time the door opens. A supplier who quotes a unit without asking about door openings and loading temperature is sizing for an empty box.
Which refrigeration unit matches which body
Three families are in common use. Engine-driven units take power from the chassis via PTO or a belt: cheapest to buy, no separate engine to service, but they only cool while the truck runs. Self-powered units carry their own small diesel engine: independent of the chassis, suitable for long dwell and for chassis whose emission behaviour makes PTO operation unattractive. Electric and hybrid units run from a battery pack or shore power, and are the right answer for urban chilled distribution but need charging infrastructure that most export markets do not have yet.
The matching discipline is simple: take the unit’s capacity at the actual evaporating temperature required, not its headline rating at 0 °C box temperature, then subtract the derating for ambient. A unit rated at 5 kW at 0 °C box may deliver well under 3 kW at -25 °C. That derating curve, not the brochure number, is what decides whether the box holds temperature on the hottest day of the year.
Why a body rated for -18 C cannot simply be reset to -25 C is explained in -18 C or -25 C.
Three specification mistakes worth avoiding
Oversizing the unit to compensate for thin panels: it works, but it burns fuel every hour for the life of the truck and hides the real problem. Under-specifying the floor: the floor is where most heat enters from the road and where the panel is most often downgraded to save cost. And forgetting the door: a wide, poorly sealed door on a 120 mm body leaks more heat in a day’s deliveries than the extra thickness saves.
What to send us to get a matched specification
Send five items: cargo type, required box temperature, maximum ambient, body internal dimensions, and door openings per day. The reply will state the panel thickness by surface (wall, floor, roof), the refrigeration unit model with its capacity at your box temperature, and the resulting duty cycle. If the requested combination will not hold temperature, we will say so and propose the change — the calculation is done before the quotation, not discovered at commissioning.