Can anyone advise me on which methods large pharmaceutical manufacturers such as Glaxo use to maintain constant pressure within their manufacturing areas? VAV?
In general , the VFD will be used to overcome the pressure drop across filter with its age and the differential pressure will be maintained by adjusting the exhaust dampers though pressure transmitter.
I am not sure about my answer but based on my understanding the pressure is generated by the air flow rate for that particular room and so if one can control the airflowrate then the air pressure can be controled. It goes back to air changes and air flowrate set for that room.
The flowmeter mesures the entry and exhit flowrates and hence the volume and controls it to the preset value to keep maintaining the pressure in the rooms.
I hope this helps. Do let me know if you have any different explanation or ideas.
I don't know about Glaxo but in the places where I worked the differential pressure was achieved with VSD linked to differential pressure transmitters.