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#1 TouchDown

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Posted 07 March 2009 - 02:42 PM

So, we have a lot of unused clean room space in our plant, with HEPA filters everywhere. Depending on the space, they are either fan driven or ducted. Majority of one's that are available are fan driven (lots and lots).

I am in charge of a project where we're are looking at building a modular cleanroom in a space where I'd like to set it up with ducted HEPAs for better control as we make the new space a new VAV zone since there are a lot of heat sources in the space and we want to make sure it's held at the correct space setpoints.

My question is this, since I have soooo many of these fan driven one's and I want to use ducted HEPAs, is there a large difference between the 2? Could I just not hook up the fan and duct one of these fan driven one's in? It looks like they have a sheet metal fitting that could be modified to accept a duct, but does leaving the fan in place increase your pressure drop across the HEPA, creating a supply air problem? Could I remove the fan blades and then use them?

We're just looking at saving cost and with these things laying around, I would like to reuse them, but I don't have time to "test" to make sure they'll work like I want.

Any feedback is appreciated. I guess I could call the HEPA mfg. as well??? But, it's Saturday and I'm watching cartoons with the kids.

#2 mizzoueng

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Posted 09 March 2009 - 03:05 AM

I cannot envision what you are talking about right now for sure, I assume the HEPAs you are talking about are self contained filters that have a fan on the inlet side to supply clean air to your clean room.

Now you want to use a HEPA fan as a VAV or a supply air duct to a VAV for a new zone in such. You could do this but you will need to account for the pressure drop across the fan and the filter for proper duct sizing and VAV sizing. Now if you are using the fan as a booster fan and it will not be needed (again, check pressure drops across filter and flow rates) then by all means you can demo out the fan blades and plug the holes and use the fan housing as duct. But you will need to take into account the pressure drop through the fan hosing, you need to follow the ASHRAE standard for calclulating the duct area differential to get the proper drop.

Once you do that you and it calcs out, you should be in the clear. I would demo the fans as nicely as possible. You could always re-install them if you need additional pressure in the room (say you add more zones and need to maintain a pressure balance).

Also, if I am way off mark, ignore it and I can try again.

#3 TouchDown

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Posted 09 March 2009 - 08:40 PM

Not too far off...

QUOTE
I assume the HEPAs you are talking about are self contained filters that have a fan on the inlet side to supply clean air to your clean room.


Ducted HEPAs just get a supply duct mounted directly onto them to support clean supply air. Fan driven include a mounted fan in the unit and normally (from my experience) pull air from a plenum that is supplied by supply air.

I may just call the Mfg. and see if they recommend using them in this application (they obviously don't make the fan one's for this application, since they sell the others). Thanks Mizzou.

#4 TouchDown

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Posted 10 March 2009 - 01:18 PM

Mizzou - here's an example after I looked them up on the internet and called the Mfg. They couldn't answer my question yesterday, so they are supposed to call me back today.

Here's a ducted HEPA module.

Fan module.

We'll see what they say...


#5 PEara

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Posted 10 March 2009 - 09:58 PM

QUOTE (TouchDown @ Mar 7 2009, 07:42 AM) <{POST_SNAPBACK}>
So, we have a lot of unused clean room space in our plant, with HEPA filters everywhere. Depending on the space, they are either fan driven or ducted. Majority of one's that are available are fan driven (lots and lots).

I am in charge of a project where we're are looking at building a modular cleanroom in a space where I'd like to set it up with ducted HEPAs for better control as we make the new space a new VAV zone since there are a lot of heat sources in the space and we want to make sure it's held at the correct space setpoints.


I usually do not design OSHPD projects, but I have couple of concerns about the question that you asked:
1)You said you want to add VAV system, since CFM in VAV system would modulate, how do you want to make sure the room always has positive pressure and fast air movement (0.1in.water, I think)?

2)Since you would like to add VAV and HEPA filers have very high static pressure drop how do you want to make sure your filter works properly when VAV is in minimum setting?

3)You would like to add VAV box, so CFM and FPM will change in the upstream of the VAV box constantly. Do you think HEPA filter still can work since face velocity would keep changing in the filter?

As I said, I am not expert in OSHPD projects but just these questions came in my mind.



#6 Art

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Posted 11 March 2009 - 02:12 AM

QUOTE (PEara @ Mar 8 2009, 07:58 PM) <{POST_SNAPBACK}>
I usually do not design OSHPD projects, but I have couple of concerns about the question that you asked:
1)You said you want to add VAV system, since CFM in VAV system would modulate, how do you want to make sure the room always has positive pressure and fast air movement (0.1in.water, I think)?

2)Since you would like to add VAV and HEPA filers have very high static pressure drop how do you want to make sure your filter works properly when VAV is in minimum setting?

3)You would like to add VAV box, so CFM and FPM will change in the upstream of the VAV box constantly. Do you think HEPA filter still can work since face velocity would keep changing in the filter?

As I said, I am not expert in OSHPD projects but just these questions came in my mind.



there is a couple ways to do it...the most common a static pressure xmtr driving the exhaust damper...as the VAV ramps down, the damper closes and vice versa...the delta air flow is maintained (the delat being the air required to pressurize the space), hence space static...
another cruder method, a mechanically balanced damper in the wall, as the P goes up, it goes open...

the static drop is known across the VAV, you just make sure the supply air that feeds it from the AHU is a constant static...
the static of the VAV discharge is not critical, it's the flow...and as long as you exhaust less than you supply, the room will be positive...
so you measure flow and set the limits when balancing...

most filters will operate over a given range of static/flow...
but if the VAV is a dual duct fan powered box, one from the room (rtn air RA), the other make-up air MUA from an AHU, then the flow will be constant...as the space calls for cooling, the MUA/AHU air damper opens, and the RA closes and vice versa...

I used to do this for a living...I built many clean rooms for pharm/bio-tech...
some with 4 pressure levels...0.30-0.20-0.10-atm...

#7 TouchDown

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Posted 11 March 2009 - 10:22 PM

Yeah, this is coming off of a shared duct for the room, with this modular cleanroom going into the corner of that same space. With the installation, we're planning on doing a test and balance for all drops off of the duct, to make sure we've pinched off in the open space enough to push adequate CFM through the HEPAs, as well forcing the VAV minimum to such a point that we make sure it doensnt' allow a "low or no flow" condition at the HEPAs, and maintaining the room positive. This is not going to be a classified space, so we don't need to worry about minimum air turns, they just want clean air over this press operation, so I don't consider it critical, as long as we maintain enough cooling into the room to maintain comfort / code as well as a positive pressure to push outward, we are OK.

#8 Alaa Kassem

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Posted 16 March 2009 - 09:41 AM

Please if any one made that FE exam for mechanical Engineering and still have books, materials or courses to send it to me or telling me which books is similar to tht FE exam for mechanical Engineering. this is my e mail for any one can help me (( alaa_abdalwaness@yahoo.com )).

please really i need help because i am so scare of this test. thank you all.

#9 TouchDown

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Posted 17 March 2009 - 05:00 PM

Probably not the thread to address this...

But, when I took the FE - it was without books present. We did reviews in after class settings at our University for prep on each section. I don't think it was specific for Mech / Elect / Chem / Civil... everyone took the same test and it was across all disciplines just assessing overall competance? Maybe it's changed in 12 years... I took it in 1996.

I would think your school would have this information and prep work. If you've been out of school and returning, then I'd put in a new thread specific to that and I know there are people who have done it after school - it was hard, so you'll need to be super prepared. Good luck.

#10 mizzoueng

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Posted 17 March 2009 - 08:33 PM

When I took it in school they (test) provided a mini MERM for us to use during the test. THis meant you had to search it as you went through the test or get a copy in advance (available for purchase from bookstore) and memorize the locations.

The test itself was not as bad as I thought it would be. More about the fundamentals that you learned in school with some more advanced questions in the specific portion that would probably not know unless you took that elective.






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