Application of CAV boxes in supply ductwork

[ikovacevic]

Dear colleagues,

My question is about one technical solution, which may be applied in pharmaceutical HVAC. We are about to decide whether to install Constant Air Volume (CAV) boxes in supply ducts for each process room.
If all dampers in supply ductwork are fixed and if supply fan is running at constant speed, then air flow rate to each room should be constant. My conclusion is that CAV boxes are not needed at all. Please note that there are no terminal HEPA filters in room ceiling, HEPA filter will be installed within Air Handling Unit.
I would like to hear opinion from other colleagues from pharma industry.
Best regards,

Ivan

 

[quark]

Fan speed is not the question. If you have HEPA in AHU, the loading of HEPA will alter the fan operating point though you maintain constant speed. Better is to maintain constant flow rate in the supply duct work by varying the speed of the fan.

If you have non HEPA diffusers, then CAV in each outlet is not necessary (but better if you have enough budget). You can have a combination of VAV and CAVs for return.

I have operated class B positive pressure zones with simple variable speed AHU and fixed supply return dampers (supply is with HEPA) without problems. The main presumption is that all HEPAs in one zone will load equally. This may create problem in future but an economic solution.