The HVAC design is driven by the cleanliness of the room (ISO class) but also by the required temperature, humidity, and pressure differential. These prescribed conditions are dictated by the process involved in the cleanroom and the comfort of the personnel working inside the room. The temperature and relative humidity (RH) precision (+/-) is also a major factor in the design of the HVAC. The heat produced by both the users and the equipment must be compensated by the air conditioning. Therefore, it is important to know how many people will be working in the cleanroom, the equipment in place and the heat it generates (watt).