[labnetwork] Filter type for the FCU

Fri Apr 10 10:45:43 EDT 2015

Jack,

Now I am getting the clear picture of the how air system works. I will convey your suggestion and feedback to my facility engineers and Will discuss about this with my installation contractors so that we will all agree upon what is best.

Once again thanks for your valuable feedback.

-Shiva

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From: Paul, Jack [Jack.Paul at hdrinc.com]
Sent: Thursday, April 09, 2015 6:56 PM
To: Shivakumar Bhaskaran; labnetwork at mtl.mit.edu
Subject: RE: Filter type for the FCU

Hi Shiva,
Thanks for the photos.  Very helpful.  It looks like you have your make-up air dumping into the ceiling space, where it mixes with the air coming from the Fan Coil Unit.  That’s good as it will give you the best consistency of temperature and humidity across the cleanroom.  The Fan Filter Units (FFU’s) are doing all the “work” of recirculating the air and the Fan Coil Unit (FCU) is only doing enough work to pull air out of the chase, across the sensible cooling coil, and into the ceiling space.

To answer your question regarding pre-filters on the FFU’s, most new FFU’s are available with the option to install a pre-filter, but it is not required.  The purpose of the pre-filter in that location is mostly to protect the fan motor from any “big stuff” like cleanroom wipers or pieces of paper that get entrained in the air stream, and particle build-up on the motor itself.  They are typically fiberglass in an aluminum (or other metal) frame.

There is a slight reduction in airflow through the FFU when you add the pre-filter, but it can be accommodated by speeding up the FFU motor if you have variable speed motors.  If you have 2 speed or 3 speed motors, you might be limited, but overall it should not upset your air balance too much.

You would see the difference in the face velocity of the HEPA on the FFU, so if you are happy with the current face velocity (which also equates to volume change or air change rate) then you could speed up the motors to until you achieved the same face velocity.

The main purpose of the pre-filter on the FCU is to protect the cooling coils in the FCU from dust build-up.  It doesn’t really do much fine particulate filtering since that job is done by the HEPA’s.  But the air going in should be pretty clean since it just came through the cleanroom.  I do understand the concern with loading the HEPA’s, but if your cleanroom users have good protocol, it is typical for your HEPA’s to last 10 years.

If you do decide to replace the current cardboard framed filters, we would suggest a MERV 7 or 8 fiberglass media filter in an aluminum or plastic frame (HDPE for example), sized to fit the FCU of course.  A MERV 17 or 18 (i.e. HEPA) or a MERV 20 (i.e. ULPA) filter will reduce the air flow through the FCU substantially due to the very high pressure drop across the filter.

Let me know if I can help further.
Jack

Jack Paul, RA, LEED AP BD+C
Laboratory Planner/Programmer
Vice President
HDR
3200 E Camelback Rd, Suite 250
Phoenix, Arizona 85018
D 602.474.3940 M 602.369.2086
jack.paul at hdrinc.com<mailto:jack.paul at hdrinc.com>
hdrinc.com/follow-us<http://hdrinc.com/follow-us>

From: Shivakumar Bhaskaran [mailto:sbhas at uchicago.edu]
Sent: Thursday, April 09, 2015 4:21 PM
To: Paul, Jack; Morrison, Richard H., Jr.; labnetwork at mtl.mit.edu
Subject: RE: Filter type for the FCU

Hello Jack,

What you saying is correct.

The cleanroom was installed before I joined here and I am trying to figure out how this works. Correct me I am wrong. As its been more than two year since it was installed I am trying to add the pieces based on inputs from different people and trying to correlate with my contractors and facility personnel.

The supply from the Air Handler unit and FCU supply are going to the HEPA filters. The return opening with the filters on the FCU are exposed to the chase area. Attaching the pdf of our systems.

Based on the interaction with other Cleanroom Managers I see that you guys are having prefilters on top of the HEPA filters, is it recommended?, I was looking into the spec of the model of the unit I have and datasheet showing prefilters on the HEPA filters. Based on my arrangement if I have prefilter installed will there be going to be effect on the air balance/pressure on the cleanroom.

Thanks for all your inputs.

-Shiva

Shivakumar Bhaskaran, Ph.D.
Searle CleanRoom Manager
The University of Chicago
5735 S.Ellis, Room 032
Chicago-60637
Ph:773-795-2297
https://searle-cleanroom.uchicago.edu/

From: Paul, Jack [mailto:Jack.Paul at hdrinc.com]
Sent: Thursday, April 09, 2015 4:12 PM
To: Shivakumar Bhaskaran; Morrison, Richard H., Jr.; labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: RE: Filter type for the FCU

Hi Shiva,
A couple of comments if I may.

Fan Coil Units are notoriously low power fans, so most of the time they are not equipped with a filter at all.  The fans cannot typically handle the pressure drop required to draw air through the filter.  I doubt that the FCU’s installed in your cleanroom will be capable of handling a MERV 20 filter, and the fan will overheat.

I may have misunderstood your air management scheme, but I believe the FCU is effectively only drawing air from the cleanroom chase and then pushing it back into a plenum above the cleanroom ceiling, correct?  Any air it draws out of the chase has come from the clean side, and that same air it pushes back into the plenum above the cleanroom ceiling will be filtered by the HEPA’s in the Fan/Filter Units.  It should not need much filtration on it, if any.  In a common cleanroom design approach, a recirculating air handler (a beefed up much larger version of your Fan Coil Unit) will not have a filter on the inlet side.  Occasionally, it might include a light duty filter (such as MERV 8) or as we sometimes call it “a wiper catcher”.

[If I’ve misunderstood and you are not using Fan/Filter Units in the ceiling of the cleanroom, but instead have a pressurized plenum, then the FCU is providing the pressure to push the air through the HEPA filters?  In any case, the air will be filtered at the ceiling before entering the cleanroom so a filter on the FCU should not be necessary]

If you do keep a filter on the FCU, you should definitely install filters with plastic or metal frames.  No cardboard.  In this case, I would even suggest you are better off without the existing filter at all.  (and the fan in the FCU will operate more efficiently as well).

Hope this helps, and hasn’t created confusion.

Regards,
Jack Paul

Jack Paul, RA, LEED AP BD+C
Laboratory Planner/Programmer
Vice President
HDR
3200 E Camelback Rd, Suite 250
Phoenix, Arizona 85018
D 602.474.3940 M 602.369.2086
jack.paul at hdrinc.com<mailto:jack.paul at hdrinc.com>
hdrinc.com/follow-us<http://hdrinc.com/follow-us>

From: labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu> [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Shivakumar Bhaskaran
Sent: Thursday, April 09, 2015 10:39 AM
To: Morrison, Richard H., Jr.; labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: Re: [labnetwork] Filter type for the FCU

FCU- Fan Coil Unit.

We have opening on each side (right/left wall) of the cleanroom were the cleanroom air is pushed out of the cleanroom and comes to the chase and then go to the FCU and then goes to the HEPA filter (we are recirculating the cleanroom air). Even though the chase area is not maintained at class 100/ 1000, we want to make sure we install  the correct filter type to maintain the air quality of the cleanroom, so that we don’t make the HEPA filters work hard with less quality air coming from the Chase air.

-Shiva

Shivakumar Bhaskaran, Ph.D.
Searle CleanRoom Manager
The University of Chicago
5735 S.Ellis, Room 032
Chicago-60637
Ph:773-795-2297
https://searle-cleanroom.uchicago.edu/

From: Morrison, Richard H., Jr. [mailto:rmorrison at draper.com]
Sent: Thursday, April 09, 2015 12:02 PM
To: Shivakumar Bhaskaran; labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: RE: Filter type for the FCU

Here is a good cross-reference guide.

We have MERV-8 as pre-filters in our makeup air unit they have plastic frames they are 2” thick. The final filter in the MAU is 4” thick Merv-15 Precision Cell ll 95% filters, again plastic frame. This air is then feed to the chases and passed into Fan Filter HEPA ceiling units. Hope this helps

I am not familiar with a FCU, what does that stand for.

Rick

Draper Laboratory
Principal  Member of the Technical Staff
Group Leader Microfabrication Operations
555 Technology Square
Cambridge Ma, 02139-3563

www.draper.com<http://www.draper.com>
rmorrison at draper.com<mailto:rmorrison at draper.com>
W 617-258-3420
C 508-930-3461

From: labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu> [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Shivakumar Bhaskaran
Sent: Thursday, April 09, 2015 11:34 AM
To: labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: [labnetwork] Filter type for the FCU

My building Facility Engineer was trying to change the filters in the FCU. He found that the FCU was installed with MERV8 type filter. I looked into the specs and it mentioned its used in commercial building.
For cleanroom the filter type is MERV20. Before we change , I want to consult with you guys on what type of filters do you use in your FCU. Our FCU is located in the Chase area of the Cleanroom ceiling.

The filter that was installed were Pre-pleat 40 LPD. The filter frame is cardboard, I am worried that this cardboard framed filter shouldn’t be used in the FCU instead it should be metal frame or plastic.

-Shiva

Shivakumar Bhaskaran, Ph.D.
Searle CleanRoom Manager
The University of Chicago
5735 S.Ellis, Room 032
Chicago-60637
Ph:773-795-2297
https://searle-cleanroom.uchicago.edu/

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