How is temperature mapping done?

A room’s thermostat can show the right value while the room is not the same temperature everywhere. The area by the door, the shelves near the ceiling, the space in front of a cooling unit and a wall that catches the sun all behave differently. Temperature mapping is done to measure that difference.

Why is it needed?

The EU GDP guidelines (section 3.2.1) ask for a storage area to be mapped before it is used, under representative conditions. Permanent monitoring devices are then placed where the mapping shows the greatest variation. Mapping is repeated at intervals set by a risk assessment, and whenever the facility or its temperature-control equipment changes significantly.

In other words, mapping is not a one-off exercise. It describes how the area behaves today, and it needs a fresh look when the area changes.

A protocol before any measurement

Good mapping starts with a written protocol. It sets out:

• the purpose of the study and the area it covers,
• the acceptance criteria, meaning the range in which the product must be stored,
• a layout showing where each sensor goes,
• how long the study runs and under which operating conditions.

The measurements come from calibrated data loggers that record at a fixed interval. Their calibration certificates go into the report too; a reading without a certificate is a reading nobody can interpret.

Where do the sensors go?

Think of the area in three dimensions. Loggers are spread across low, middle and high levels. They are not bunched in one spot but distributed so that together they represent the whole area. These points in particular are covered:

• near doors and loading docks,
• along outside walls and windows,
• around lights, heaters and cooling units,
• in the middle of the area, as a reference.

In racked warehouses the difference between the top levels and floor level gets its own attention, because warm air rises and the upper levels can behave differently.

How long should it run?

Rather than a fixed number of days, the right question is whether the study covers the area’s normal operation. The hours when doors open most, working and non-working days, and the cycles of the cooling system should all fall within the recording period.

Where the outside climate affects the area, mapping is done in both the hot and the cold season. It also allows for the area behaving differently when it is empty and when it is full.

Mapping and continuous monitoring

Mapping is a study done over a defined period, and it shows how an area behaves. Continuous monitoring runs every day with permanent sensors, and it shows whether the condition is being kept.

The two complement each other. Mapping decides where the monitoring happens: the permanent sensors go where the mapping found the hottest and coldest points. Over time, the monitoring data can in turn show whether a new mapping is due.

What should the report show?

Alongside the raw data, a mapping report shows the hot and cold spots, any readings outside the range and their likely causes, where the permanent monitoring sensors should go, and any zones that should not be used for sensitive products. A good report is written clearly enough for the next person to repeat the same study in the same way.

We explain where mapping fits within GDP in What is GDP?, and the risks a product meets after leaving the warehouse in Where does the cold chain break?