One of the most important aspects of cleanroom design is HVAC and airflow in the room. In addition to incorporating a robust HVAC control system and HEPA filters, many cleanrooms also include pressurization. Positive pressurization is particularly beneficial to rooms that handle sensitive processes.
Air typically flows down from the ceiling through HEPA filters, sweeps the floor and is exhausted through grilles in the wall. The air is then pumped back up to the ceiling where it is sent back through the HVAC units. The cycle continues as the air flows back down through the HEPA filters back into the cleanroom.
To achieve positive pressurization, more air is required than that which is already in the room. Outside air is added to increase the amount of air pressure in the room. The cycle then continues with air circulating in the cleanroom, mixed with additional air from the outside. Thus, the air within the cleanroom is now at a higher pressure than the air outside of the cleanroom.
Maintaining this higher level of pressure does require some extra work. The extra air, or “make-up air”, needs to be at the correct temperature, humidity, and cleanliness. Furthermore, measures need to be put into place to make sure that the room doesn’t get over-pressurized. All of these items are highly dependent on the proper HVAC units.
Despite good HVAC systems, pressurization is also greatly dependent on the quality of the cleanroom. Since the cleanroom will be at a higher pressure than the area outside the room, the cleanroom must be built with the utmost quality. This includes being well sealed to minimize air leakage and to prevent contamination from infiltrating the clean space. Lastly, the highest pressurization should be in the cleanest spaces and should cascade to a lower pressure for less clean spaces
Some rooms may require negative air pressure. Negative air pressure involves taking a portion of the air out of the room completely. This is typically for very specialized processes that often involve hazardous chemicals. The negative pressure usually occurs under a hood and then is sucked out of the room. Depending on how harmful these chemicals are, they may need to be filtered again before they are released into the outside air.
As with most things associated with a cleanroom, it is important to consult with an expert. HVAC systems are highly important and should be installed and configured properly. Much of the activity that is conducted within the cleanroom is contingent upon the HVAC system functioning properly.