Temperature Mapping a New Cold Room: The Study That Proves It Holds Spec

A cold room controller shows one number — the temperature at the sensor, usually near the evaporator return. That number can read a comfortable 4 degrees while a pallet in the far corner sits at 9, and a carton by the door swings to 12 every time it opens. A temperature mapping study is how you find out what the room actually does, everywhere, before you trust it with product. For anyone storing pharmaceuticals, vaccines, or high-value perishables, it is not optional.

What mapping proves that a controller cannot

The control sensor manages the refrigeration; it does not represent the whole room. Air temperature in a cold store varies with distance from the evaporator, height, proximity to the door, how the racking blocks airflow, and how full the room is. A mapping study places many independent, calibrated data loggers throughout the space and records them together over time, so you can see the real distribution: where the cold spots and warm spots are, how big the spread is, and how the room behaves during and after a disturbance. The output is a picture of the room, not a single point.

How a mapping study is run

• Sensor grid. Loggers at all eight corners, the centre, beside the door, at the evaporator air discharge and return, and at several heights — floor level, mid, and just below the ceiling. A larger room needs more points. One logger sits outside as an ambient reference.
• Logging interval. Short — every one to five minutes — so that door openings and defrost cycles show up rather than being averaged away.
• Duration. At least a continuous 24 hours, and often 48 to 72, to capture every defrost cycle and a full day-night ambient swing.
• Empty and loaded. Run it once empty to characterise the room itself, then again fully loaded, because product mass and blocked airflow change the result significantly.
• Challenge tests. A door held open for a set period, and a power-off period followed by recovery — the second one matters a great deal in Bangladesh.

Reading the results

From the logged data you pull the minimum, maximum and mean at each location, the overall spread across the room, and for pharmaceutical work the mean kinetic temperature, which weights the excursions by how damaging they are. You are looking for any location that goes outside the product’s allowed range, how long recovery takes after the door and power challenges, and whether any spot is consistently the worst. That worst location is where you then place your permanent monitoring probe — monitor the hardest point, not the easiest — and where you avoid putting the most sensitive product.

The reference standards

For pharmaceutical and vaccine storage the recognised guides are the World Health Organization’s Technical Report Series 961, Annex 9, and the PIC/S guidance on good distribution practice; national drug-regulatory expectations follow the same logic. Food operations run a lighter version aligned to their HACCP plan. Whichever applies, the principle is identical: qualify the room against a written protocol, keep the raw data and the report, and be able to show it. See cold chain compliance for pharmaceutical and vaccine distribution.

When to map, and when to map again

Map a new room before first use, after any significant change — new racking, a relocated or replaced evaporator, a change in how the room is loaded, a capacity increase — and periodically thereafter, commonly once a year, plus after a major repair. In Bangladesh it is worth timing at least one mapping for peak summer, when the condenser works hardest and ambient load is greatest, and making sure the power-failure recovery test reflects a realistic load-shedding duration rather than a token few minutes. Pair the study with continuous monitoring so you catch drift between mapping exercises — see IoT temperature monitoring and humidity control in mini cold storage.

Build mappability into the room

Some rooms are far easier to keep uniform than others: an evaporator sized and positioned for even throw, racking laid out so air can circulate rather than being dammed by a solid block of pallets, well-sealed doors, and enough refrigeration headroom to recover quickly after an opening. Those are design choices made at purchase, and they are the difference between a mapping study that passes cleanly and one that sends you back to move equipment. Related reading: pharmacy and medicine storage and condenser and evaporator placement.

Choosing and calibrating the data loggers

The study is only as trustworthy as the instruments. Use enough loggers to cover the grid — a small room might need nine to fifteen, a large one many more — and they should all be the same type with a resolution and accuracy suited to your tolerance band; tighter product limits need better instruments. Every logger must carry a current calibration certificate traceable to a recognised standard, and it is good practice to do a quick pre- and post-study check by reading them all together in a stable reference (an ice bath, or a calibrated chamber) to confirm none drifted during the run. Loggers that disagree at the reference get excluded and the affected positions re-run.

Writing the mapping protocol before you start

Decide and write down, in advance: the acceptance criteria (the temperature range every location must stay within, and any short-excursion allowance), the number and exact positions of loggers with a labelled diagram, the logging interval, the total duration, the empty and loaded conditions, the door-open and power-off challenge parameters, and how the data will be analysed. Agreeing the pass criteria before you have the data is what makes the study a genuine test rather than a rationalisation. Keep the protocol, the raw logger files, and the final report together — an auditor or a regulator will want to see all three.

From mapping report to standard operating procedure

A mapping study is not filed and forgotten; it feeds your daily operating rules. The worst-case location becomes where your fixed monitoring probe sits and where you never place the most sensitive stock. The recovery time from the power-off test sets how long you can tolerate a load-shedding event before you act — move product, start the generator, escalate. The door-open result sets a rule for how long the door may stand open during loading. And the map tells staff which zones are for fast-moving, less-sensitive product and which are the tightest, most stable spots. Re-map after any change to racking, refrigeration or loading pattern, and at least annually, ideally timed for peak summer. Pair it with continuous IoT monitoring so drift between studies is caught early.

Who should run the study

A food cold store with modest tolerances can often run a credible mapping in-house, provided someone owns the protocol, the loggers are calibrated, and the analysis is honest about excursions. Pharmaceutical, vaccine and high-value applications usually bring in a qualification specialist, both for the instruments and for the independence — a regulator or a customer audit gives more weight to a third-party report against a written protocol. Whichever route, the deliverables are the same: the approved protocol, the raw logger data, a report that states pass or fail against the pre-agreed criteria, and a list of the actions taken where a location failed. Keep all of it with the room’s records for as long as your sector requires.

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