Temperature mapping measures how temperature is distributed across a storage area and finds its warmest and coldest points. The practical output is where the permanent monitoring sensors go and which zones stay free of product. The figures below come from WHO's temperature mapping supplement (Supplement 8) and from the Turkish TİTCK GDP Guideline.
Sensor grid and count
WHO asks for sensors on a grid every 5-10 metres. In an area with a ceiling of 3.6 metres or lower, each grid point is measured at three levels: floor, 1.2 metres and 3.0 metres. Example area: 30 × 20 metres with a 3.6 metre ceiling; the dimensions are chosen to keep the calculation simple.
| Spacing | Grid points | Loggers (3 levels) |
|---|---|---|
| 10 m | 4 × 3 = 12 | 36 |
| 5 m | 7 × 5 = 35 | 105 |
So a 10-metre grid gives 36 loggers and a 5-metre grid gives 105. All loggers are set to the same start time; if the clocks differ, events cannot be matched to the record.
Recording time and calibration
A warehouse at ambient temperature is logged for at least 7 consecutive days: 5 working days and 2 weekend days. Cold rooms and freezers are logged for 24-72 hours, longer if justified. The recording interval is set between 1 and 15 minutes. At a 1-minute interval one logger produces 10,080 readings in 7 days (7 × 24 × 60), and at a 15-minute interval 672 readings (7 × 24 × 4); the device memory is chosen to match.
Each logger needs an NIST-traceable three-point calibration with an error no greater than ±0.5 °C, valid within the current year; otherwise it is recalibrated annually. The certificates go into the report.
| Area | Minimum duration | Season |
|---|---|---|
| Warehouse at ambient temperature | 7 consecutive days | If needed, two studies: warmest and coldest season |
| Cold room, freezer | 24-72 hours | Two seasons usually not needed |
Empty and loaded store
A map taken in an empty store does not describe a loaded one. WHO asks for the temperature profile both empty and under normal load, because racking and product change the airflow. The time outside limits after a door opening is part of the acceptance criteria: WHO allows a maximum of 30 minutes, and the protocol states it. The acceptance range, for example 2 °C to 8 °C or 15 °C to 25 °C, is written into the protocol beforehand.
What follows from the result
Permanent monitoring sensors go to the hot and cold spots shown by the map, even where door openings affect them, and the alarm limits are set from that data. An average alone decides nothing; WHO recommends looking at the overall high and low trends as well as the single highest and lowest values.
Zones close to cooling coils, cold air streams and heat sources are marked as areas without product, and WHO asks for these zones to be defined. The TİTCK guideline asks that stacking in a cold room does not block the airflow in front of the indoor unit, and it recommends perforated shelving.
Hot and cold spots can differ between summer and winter, so WHO asks for them to be determined by season.
When it is repeated
The study is repeated when racking, equipment settings or anything else affecting airflow changes. WHO gives a three-year periodic repeat as an example. The TİTCK guideline asks for a repeat after a risk assessment or a significant change in the facility. The protocol, logger records, location plan, raw data, analysis, deviations and approvals are kept together.