I have a request from a customer concerning the validation of a cold room with a size greater than 20m3. To validate the temperature, the norm NF X 15-140 specifies 15 sensors for a volume between 2 to 20 m3.
there is no hard and fast rule that these many have to be placed. I have seen only references till date that there should be like this. It depends on your risk assessment considering all the factors like location of supply, height etc where you place sensor for mapping.