Negative pressure in Room and air balance 1

[Fenixseravgon]

I have a doubt:

If a have a negative pressure in a room, does it suppose that i have a negative air change?

Because my extraction is bigger than my inyection of air to the room. these is rigth or not?

I have to report my air changes in a pharma instalation and i have that doubt.

Please help me.

Sergio Avila

 

[KiwiMace]

Not right. Even your doubt is doubtful. Everything is relative.

If you have a little negative pressure in a room, it is still positive to the general universe and likely to atmospheric pressure... and some other space closer to the supply fan.

Negative pressure can be obtained with any number of air changes - air changes can be had as long as there is air passing through a room. Look at your air flow and calculate the air changes based on that data and the volume of the room.

 

[quark]

KiwiMace,

Biological production units maintain areas negative with respect to atmosphere, particularly when viruses or GMO are being handled.

Sergio,

You calculate ACPH based on supply flow rate and not net flow into the room. ACPH indicates how many times your room air is being refreshed (by filtration) to maintain the required particualte level.

 

[mauricestoker]

I would recommend reviewing USP 797 if you are doing pharma. Whether you have a positive or negative differential pressure, or both, would probably depend on that. For toxic compounding you would need a negative enclosure, such as a bio cabinet or other ISO 5, surrounded by a positive enclosure, generally ISO 7. Entry would be through a vestibule under negative relative differential pressure compared to the ISO 7, for personnel and material movement. The USP 797 has some simple figures with it to illustrate the relative pressure differential for compounding and toxic compounding.

If you are handling viruses, you would probably be in a BSL-2, 3 or 4, which is an entirely different requirement from the BMBL.

If positive, I count air changes by supply for the ISO ACH requirement, and look for a 0.05 IWG at balance by dampering the exhaust. For negative I go by ISO ACH requirement on the supply side, and damper back the exhuast at balance for the 0.05 IWG. A magnahelic on the wall before entry should be considered for operations. Differential flow indicates relative differential pressure. The amount of flow difference needed is reflective of the leakiness of the enclosure.

 

[KiwiMace]

OK quark, but the OP is still not right.

 

[ChasBean1]

Calculating an air exchange rate for any space is based on the higher of the flows (exhaust or supply).

 

[quark]

I am not sure about other industries but it is supply in Pharma. Excess return air, in case of negative pressures, is a result of leakage from other areas. This is considered to be untreated.

 

[ChasBean1]

Treated or untreated, sucking out air and re-injecting it is ACH101. Air is exchanged regardless of passing through whatever supply filter media is in place.

 

[317069]

I think it is a helpfull link

http://www.eng-tips.com/viewthread.cfm?qid=43928