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What order should you deliver frozen, chilled and ambient stops?

Every mixed load starts the same argument at the dock. Do you deliver in the order that protects the coldest product, or in the order that gets the vehicle back soonest?

The standard order, and the reason behind it

The standard order is frozen, then chilled, then ambient, and the reason is exposure. Frozen product sits furthest from the outside temperature, so it gains heat fastest every time the doors open, and some of that damage is permanent: product that partly thaws and refreezes does not come back to the texture it had. Delivering it first means it survives the fewest door openings.

Chilled goes second for the same reason with less urgency behind it. Ambient goes last because ambient does not care.

The delivery order also decides how the vehicle is packed, because a run is loaded in reverse. The last drop goes in first, against the bulkhead. The next drop sits by the doors, where it can come out without exposing everything stacked behind it. Change the sequence after the vehicle is loaded and you have added a rummage at every stop, with the doors open while it happens.

Why the quickest route usually wins

The quickest route usually wins because the sequence is a preference and the geography is a fact. If the frozen drop sits on the far side of town with three chilled drops between here and there, driving the textbook order means crossing the city twice to honour it.

That detour is not free for the load. Every extra half hour on the road is another half hour the chilled and ambient stock spends on a vehicle in traffic, with the refrigeration unit working against the outside temperature the whole time. Forcing the order to protect the frozen goods can leave everything else on the vehicle worse off than it would have been.

The detour is not free for the business either. Refrigerated delivery is priced tightly, and an extra thirty minutes on a run is not a rounding error - on a thin margin it is the job's profit. That is a reason to take the trade-off seriously, not a reason to settle it with a rule.

What a door opening actually costs

A four-minute door opening on a chilled body costs about 10°C (18°F). Measured on our own vehicles, a body holding 5°C (41°F) with 30°C (86°F) outside is sitting near 15°C (59°F) by the time the doors close again, and takes roughly fifteen minutes to settle back to setpoint.

Published figures are gentler than that, and they are usually measured somewhere else. A widely repeated table puts a five to fifteen minute opening at a 2-4°C (4-7°F) rise with thirty to forty-five minutes of recovery, but that is a loading dock: doors opening into a sealed, cooled, sheltered space. A kerbside drop opens onto whatever the weather is doing.

These are our numbers, from vehicles running standard truck-mounted refrigeration units, and they are not a constant. Unit capacity, insulation, outside temperature and how full the body is will all move them.

An emptying vehicle is a warming vehicle

How full the body is matters more than most operators expect, because the product is the thermal mass. A full vehicle holds temperature largely because of what is stacked inside it, and as the run empties that mass leaves with the stock. The same four-minute opening costs more at drop eleven than it did at drop two. The vehicle is at its most vulnerable at exactly the point in the day when everyone assumes the hard part is behind them.

How to tell which runs need re-sequencing

The answer comes off the temperature record, not off the route. Record every run, including the ones nobody is worried about, because a run only tells you something when you can compare it to the same run on a different day.

A spike at every stop is normal. That is the door, and it should fall back. What matters is the baseline underneath the spikes: if the low point after each recovery is a little higher than the low point before it, the unit has stopped catching up, and the stop where that begins is the stop that should have come earlier.

Run the same route on a cool morning and a hot afternoon and the answer changes. A sequence that holds through winter can start drifting by drop eight in summer, which makes this a seasonal decision rather than a permanent one. That is also why a rule fixed at the planning stage is the wrong tool for it.

The same records do a second job. They answer the receiver who wants to know whether the load stayed in spec on the way to them, and they export as a history of the run when an auditor asks for one.

Changing the order without replanning the run

Once the records point at a particular run, the change is a re-sequence rather than a rebuild. Move the frozen drop up the list, look at what it does to the finish time, and decide whether those minutes are worth the degrees. That decision needs both numbers in front of you at once, which is the part most planning tools make hard.

YowieTech Route Planner shows a run as a list of stops you reorder directly, with each stop's temperature zone visible while you do it, and it keeps the temperature record and the cost of the run afterwards so the next version of this decision has evidence behind it rather than an opinion.

The thing worth doing on Monday is smaller than replanning anything. Pick the run you trust least in hot weather, record its temperatures for a week, and look at where the baseline stops recovering. You will either find nothing, which is worth knowing, or you will find one stop sitting in the wrong place.