Where a body or cold room has a single sensor, what it measures is the temperature where it sits, not the average of the space. A sensor in front of the discharge reads colder than reality and one beside the door spikes at every opening, so decide first what you want to watch.
| Point | What it shows | What it is used for |
|---|---|---|
| Discharge outlet | Air the unit is producing | That the unit is running |
| Return air | Average air of the body | Unit control |
| Hardest zone of the load | Worst case | Product safety decisions |
The hardest zone differs from body to body. Cold air leaves the discharge, circulates around the load and returns, and where circulation is weakest depends on how the load is stacked. Instead of guessing, find it with several sensors on a trial run and put the permanent point there; if the product is within target at that spot, it is within target in the rest of the body too.
An air sensor responds quickly, a product core slowly; because product temperature is what counts in audits and commercial disputes, a logger goes among the product on critical shipments. For quick-frozen food the regulation requires ambient temperature to be measured and recorded; in a retail cabinet the thermometer reads at the maximum load line, on the return side of the airflow (Communique 2014/48, Article 4).
- Do not put the sensor directly in front of the discharge
- Keep at least one point in the hardest zone of the load
- In a store, monitor the door zone and the farthest rack together
- Record positions on a sketch
