Air Balancing in Pharma

[zer0net]

Hi everyone,
I'm currently tasked with balancing air in a new pharma company and it would be great if someone can tell me if i'm on the right path.
On the main manufacturing area, there are about 30 rooms, each room has most rooms have 1 to 3 supply air diffusers and 1 to 2 return grills (depending on the size of the room), the biggest room has about 18 supply diffusers and 3 return. We have 2 HAAKON AHUs handling air on this floor. What we want to do is keep the corridor pressure to be higher than that of the room, so when the door opens air from corridor should flow into the room and no air should come out what so ever.
I'm playing around with this and I have set the supply fan to 45Hz and return fan to 55Hz. I did this because I think that by setting return fan to be higher than supply I will force the air from corridor to the room and also when the door is opened, the return grill should be able to handle large influx of air. Doing so magnahelic shows me differential pressure of approx 15Pa (after adjusting return damper for each room).

But I dont know if this method is efficient or even right. Can anyone please confirm/offer suggestions

Thank you

 

[ChasBean1]

Maybe slow on responses because questions remain. Are there terminal boxes? Do spaces return all air or exhaust some? If your AHUs are the source of outdoor air, just setting the return VFDs to 55 Hz and the supply VFDs to 45 Hz will probably ensure no fresh air is taken in by the units unless economizer dampers are at 100% OA.

Return should track supply to maintain the desired minimum outdoor air value. Balance negative rooms with less supply than exhaust/return; make up differences in common/neutral areas.

 

[zer0net]

Hi ChasBean1, thanx for replying
Due to ridiculous amount of humidity outside we reduced the OA damper to about 5-10% and same with EA damper, so almost all of the air is returned at the moment.
But do you think it makes sense to run return VFD at 55Hz and supply VFD at 45Hz?

 

[davidcamell]

If so much of the air is recirculate (correct me if I'm wrong: room air and corridor air mix at the unit before being redistributed?), then what is the goal in keeping a higher differential pressure in the corridor?

Also, are there terminal boxes? Are they variable volume?

I might be incorrect, but isn't the point of the VFD's to have varying supply and return airflows? If the system is variable supply/return, wouldn't you use a pressure sensor mounted in the duct mains to modulate the VFD and therefore the pressure/airflow?

Are there fume hoods or process exhaust in these rooms?

 

[zer0net]

Davidcamell,

Yes the air is mixing, but its going through filters before it mixes, and when it mixes it passes through more filters and finally passes through HEPA filter before entering manufacturing area, so there wont be any cross contamination that way.
We dont have any terminal boxes.

For us the main thing is to keep (15pa) differential pressure between the room and corridor.

only one room has fume hood, and each room will have process vacuum.

 

[ChasBean1]

Try not to confuse the outdoor air (OA) damper position with the % of OA being taken in. For example, if you are at minimum OA (OA open 10-15%, mixed air damper fully open, and relief damper closed) and your return is set at 55 Hz moving 50,000 cfm and your supply is at 45 Hz moving 42,000 cfm, you are taking in no outdoor air. There is 8,000 cfm going out the intake. And this, in addition to your building exhaust will make an excessively negative building.

Whatever net negative there is in the building will be made up by infiltration, which means you'll be conditioning that air anyway, except in locations that could cause localized condensation and mold growth rather than at the AHU coil.

To minimize your outdoor air, set the return air flow equal to supply flow minus building exhaust flow. If you have an enthalpy comparison economizer that works right, don't worry about fixing OA dampers to a certain position. The ridiculous amount of humidity outside will be accounted for in the enthalpy comparison; dampers will be at your set minimum if OA humidity is high.

Set the AHU like this, then focus on the space to space distribution/balancing.

 

[dtse86]

I work in semiconductor cleanrooms and typically we try to control particulates using POSITIVE pressurization. Clean spaces are under positive pressure so that particles always flow to a less clean space. In the fab I am currently working in, we return our air into a dirty return air chase and use filtered fan units to push the return air from the plenum back into the fab. Depending on what kind of Class of clean room you plan on certifying in, your coverage can range from 30% to 100%.

 

[ChasBean1]

You're right about clean rooms and typ. pharmacy manufacturing areas, but the positive pressure is switched to negative for applications where they're manufacturing toxins, e.g., for chemotherapy, etc.

 

[mauricestoker]

USP 797 requires the same ISO class considerations for ACH, toxic compounding requires negative pressure for employee protection. Large difference is outside air; for USP 797 toxic compounding 100% OA is generally required.

I think you need to provide a few more details before any realistic comments could be offered. What type of supply system, controls, what is driving the VFD's, etc.

Are you balancing the system or designing it? I think suggestions would be based on that point. If you are trying to balance it, set the exhaust damper for ACH for ISO/contract requirements and adjust supply to meet differential requirement. Repeat for each room. Record static pressure for setpoint control.

Hopefully the hood is off its own exhuast. Is it a fume hood or BSC? That will change criteria and control. If a BSC, include time and money for NSF 49 cert, unless you hold a cert. That would be in addition to the clean room cert.

 

[dtse86]

I thought that when dealing with HPM distribution or reactions, the process needs to be performed in an exhausted enclosure which is typically either a vacuum or a heavily exhausted cabinet. The room which the tool or equipment sits in can remain positive pressure so that the operator has a lesser chance of being exposed. Typically that means that the exhaust requirements for the production equipment will almost always cover the requirements for air change.

That's what the Safety department here seems to tell me anyways.

 

[mauricestoker]

HPM means that product must be protected. If no listed or characteristic materials are given, then employee protection is not required. That would be comparable with non-toxic compounding where room environment would presumably be positive (or an immuno-suppressed room). If toxics are used, then employee protection must be included. That would be where a glove box or bio safety cabinet would come in. For immuno-suppressed I've recommended moving to microenvironment or including a vestibule where large mammals are involved.

If you have a glove box, then HVAC and controls are much easier, surrounding ISO level should be lower, and you don't need negative differential pressure. That would definitely be the way to go from a cost and energy standpoint.

If you have a bio safety cabinet,then some more expensive considerations come in. For toxics, the room must remain negative so as not to expose the rest of the facility. Your safety officer must have been thinking of glove box and specficially not fume hood or BSC. I've gotten around the issue by including a positive anteroom, same ISO level as BSC room. Also helps with managing door swing pressure changes(by interlocking the doors). If the Safety Officer meant that to include for BSC, then the Safety Officer should be moved to directly outside of the room to filter out toxics with their lungs.

I finished a USP 797 earlier this year and wished over and over they would glove box or reach a decision on what BSC would be used. Did convince them to move toxic to an upper floor and non-toxic to the basement, as it meant a six figure difference in cost. Consulted on another job, same situation, cost difference of about $550,000. One more of those jobs and I'll be spending all my money on Rogaine and hair weaves.

 

[HEC]

Can the OP draw a sketch of the arrangement and perhaps provide some guide on why the manufacture room needs to be negative. Had a similar issue in a Pharma plant where we needed to contain a flamable zone.


Mark Hutton

 

[mauricestoker]

I would suggest reading NFPA 45 for an understanding of why any environment needs to be negative. Under USP 797, for toxic compounding, the same rationale is given. The earlier ASHRAE Applications coverage was rather weak under wet or potentially airborne contaminatns, but covers it much better in the 2007 version of Applications. It shows both postive and negative environments for clean room under chapter 16.

The glove box or isolator eliminates need for much of the air changes and control requirements. Unfortunately, a lot of customers do not like glove box or isolator. A BSC can give product protection, but it does not provide personnel protection. Personnel protection must be provided not only for the operator, but for the facility and emergency responders as well. Even further, the O&M personnel must be protected, which is why ANSI Z9.5, ASHRAE 62.1, IMC and USP 797 includes requirements for duct negative pressurization, minimum duct velocity, exhaust stack height and discahrge velocity, duct construction, subducting, backdraft dampers, alarm, etc.

If using postive pressure environment with toxic/flammable materials, where does the toxic/flammable material drift to if not the surrounding facility. If occupied, and the personnel are literate, they should be calling for OSHA investigation under those conditions. I would not want to be exposed to uncontrolled levels of unknown toxic material, and would not want to do that to anyone else, including repsonders and O&M personnel.

 

[slynk]

In a pharma facility, corridors are usually kept at a higher pressure as a way to protect personnel and cross-contamination of the products between rooms.

zeronet: I'm also doing something similar. Do your production area and corridors share the same AHU? If each area has its own, then setting 55hz for return and 45hz for supply for the production area makes sense. However, if they share the same AHU, then it's really up to the adjustment of dampers in the rooms to ensure the DP is there. Anyway, I think you may have completed your task by now. Hope it went well.

 

[sridhar1312]

Corridor is clean and all the rooms are different substance and hence the clean corridor has to be higher pressure and room can take corridor air which is clean.

Yes you can adjust the exhaust damper to maintain the differential pressure between corridor and room. Mostly each room shall be with separate unit to avoid any cross contamination.

 

[zer0net]

Slynk,
I havent completed it as yet, got side tracked by higher priority projects, and yes both the production rooms and corridors share the same AHUs. My logic behind setting return higher than supply is, if i reduce the supply dampers in each room to minimum and then open the corridor supply to maximum, and since there is no return in the corridor I should increase the return in each room thus forcing air in each room from corridor. It seems to give me the pressure I want, almost in every room, however... I still need to maintain +ve pressure even when the door is open (even +1 will do).

 

[mauricestoker]

If they are on the same AHU, then I would recommend a net neutral balance. Corridor would be provided air at the net volume balance (set at TAB) needed to make relative static pressure differential between positive corridor and negative work rooms. Certification of room includes ACH; for a negative environment that is measured off the exhuast. Set ACH on exhaust to meet ISO/contract requirements, then set supply damper to meet relative negative differential requirement.

Most will have to be set at TAB, then final sheaving done, unless you have VFD's (which are nice against filter loading, TAB, and future changes). As room ACH's are pretty much set for work areas (volume flow for ISO is going to greatly exceed any comfort flows), only the corridor needs to be estimated for air flow. That would probably be the greater of PHARMA requirements (which in some cases requires surrounding ISO 8) or ASHRAE 62.1, or differential air flow volume needed between corridor and work room. That is pretty much a ball park guess, unless it is existing construction (to address any leakiness factors)where you can do some field testing before setting balance flows for the TAB.

If the corridor and work areas are off the same unit I would recommend a net neutral balance (assuming you need to have filtered supply air). If supply volume is less than exhuast volume, where does the necessary make-up air volume (which will be necessary to maintain the relative differential static pressure difference betweeen corridor and work area)come from? That would be either from increased infiltration or taking in air from another part of the building (which the same level of supply air filtration might not be required).