Can any one elaborate to me the relation between temperature, relative humidity and differential pressure.
Assuming you are talking about a clean room, these are values that must be controllable and were probably set during start up of the facility. Guidelines mention no specification for temperature and humidity. These you must set yourself based on the requirements of your process.
ISO14644-4 Annex A: The pressure differential between adjacent cleanrooms or clean zones of different cleanliness level should lie typically in the range of 5 Pa to 20 Pa, to allow doors to be opened and to avoid unintended cross-flows due to turbulence.
Don’t forget to document why you choose certain settings!