[labnetwork] FW: Temperature specification for facility process chilled water

Fri Sep 18 15:38:19 EDT 2015

Bill and Tim, 

Please let me chime in here. Over the past 32 year designing, building and operating PCW systems at various high tech facilities here are my thoughts:

1.   Temperature control: tighter temp control range could be easily achieved by using a "Modulating V-Port control ball valves with pneumatic actuators" compared to other types of control valves as long as you have a relatively stable CHWS temperature.

2.    Bacteria control:
       a) open loop: usually such a system includes a storage tank equipped with nitrogen purge to minimize CO2 absorption, hence very low or no bacteria growth. PCW tanks that don't have nitrogen purge will develop bacteria and biofilm growth on the piping surface. 
      b) closed loop: closed loop systems filled with RO water don't experience frequent bacteria growth. Sterilizing the system once every couple of years then refilling with RO water is recommended. You can also add a biocide but it will defeat the purpose if you need to maintain resistivity at a certain level. However, bacteria growth could be better controlled by adding a bacteria UV light in a side stream connected between pumps' discharge then back to the PCWR pipe upstream of the air separator snd pumps suction.

3.   Resistivity control: 
      a) open loop: as Bill stated this is usually achieved by the bleed and feed method. DI water is added to the tank when water resistivity drops below a preset level. Excess water overflows from the tank to the AWN. This method uses more water and takes longer to raise resistivity to the preset level. A more effective way is to bleed PCW from the PCWR pipe by activating a side stream solenoid valve then adding DIW  to the tank until the desired resistivity level is achieved. This will take less water and time to achieve the preset resistivity level. 

     Another way to control open loop and closed loop resistivity is by running a PCW side stream  from the pumps' discharge  into ion exchange beds then return the water back to the tank or pump suction respectively. Adding a bacteria sterilizing UV light to this side stream will
Be an economical way for controlling bacteria growth in the PCW system. 

15 years ago we were invited by Novellus  to evaluate their open loop PCW system which developed very high bacteria levels due to the absence of nitrogen purge. Prior to our involvement Novellus attempted to sterilize the system using sodium hypochlorite. Unfortunately they ended up destroying the phosphating layer on the interior surface of the vacuum pumps and causing them to rust.  Adding pain to misery the system developed iron eating bacteria which resulted in destroying their vacuum pumps which had to be replaced at $54K a piece. 

In conclusion, depending on the system that you currently have you can design and install one or a combination of the features described above that will serve your needs. Please feel free to call or write back for any questions.  

Regards

Rizik Michael
Cell: 408 718 0927
Sent from my iPhone

> On Sep 17, 2015, at 7:59 PM, Bill Flounders <bill at eecs.berkeley.edu> wrote:
> 
> No biocide or corrosion inhibitors on the pcw loop.
> Piping is copper. 306 SS was rejected for cost savings. 
> CPVC would have been preferred and additional cost 
> savings but initial code interpretation would not allow CPVC 
> since it does not meet 25/50 smoke/flame spread requirement.
> 
> Resistivity target is 200kohm.
> At 175k, tank dumps ~20% system volume and is refilled with RO.
> Resistivity recovers to ~275k. System resistivity gradually decreases
> over 3-5 days and cycle repeats. Recurring fresh water input is what
> avoids need for biocide or inhibitor. 
> 
> If any failure of pcw pump/flow - system automatically crosses over
> to single pass ICW. Resistivity spec is bypassed. When PCW flow
> is restored, resistivity control is reimplemented and 4-5 tank dumps
> required to restore system to normal. A picture is worth 1000 words:
> Appended graph summarizes resistivity as function of time for the 
> past 1month. 2 cross over events to ICW are noted. 
> 
> Bill Flounders
> UC Berkeley
> 
> 
> <PCW_Resistivity.jpg>
> 
> 
> 
> Miller, Timothy J wrote:
>> Iain,
>> 
>> Normally Jeff Kuhn would answer this, but he is out this week on family business.
>> 
>> All of the components in our PCW system are stainless steel, CPVC, or fiberglass.  We haven't really worried about corrosion preventers since the building was commissioned.
>> 
>> In ten years of operation we have had one problem with bacteria.  The system was dosed once with biocide, which was then removed by dilution.
>> 
>> No UV sterilizers or mixed beds.  If there is a catastrophic loss of water we can refill from the RO on the UPW system, which runs 1-2 MegOhmcm.  If the resistivity of the water drops below .95 Meg the system is topped off with concentrate water from the ultrafilters on the UPW system (18.2 Meg) with the excess water overflowing to drain until the resistivity returns to 1.05 Meg.  Very simple and very inexpensive.
>> 
>> Tim
>> 
>> Timothy J. Miller
>> Purdue University
>> Birck Nanotechnology Center
>> 1205 West State Street
>> West Lafayette, IN 47907-2057
>> 765-427-4712
>> 
>> 
>> -----Original Message-----
>> From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Anteney I.M.
>> Sent: Tuesday, September 15, 2015 2:16 AM
>> To: Dennis Schweiger
>> Cc: Vito Logiudice; labnetwork at mtl.mit.edu
>> Subject: Re: [labnetwork] Temperature specification for facility process chilled water
>> 
>> Denis,
>> 
>> I'm particularly interested in your comment about polishing the loops to get 1 mega-ohm resistance as we have struggled to do this especially when we dose the system with biocide and corrosion inhibitors. What are you using to polish the system, what inhibitors/biocides do you use and how do these affect the conductivity.
>> 
>> Regards
>> 
>> Iain
>> 
>> Cleanroom Manager
>> University of Southampton
>> 
>> Sent from my iPhone
>> 
>> On 15 Sep 2015, at 00:36, Dennis Schweiger <schweig at umich.edu<mailto:schweig at umich.edu>> wrote:
>> 
>> Vito,
>> 
>> here at UofMichigan, one of our PCW systems runs about 62.5F (16.9C) with a daily deviation of about 1F. The second runs about 59-60F (15C).  It too has a daily deviation of about 1F.  For both systems we may see a seasonal deviation of 3-4F as the main chiller plant transitions from "free cooling" to the use of chillers to create cooling water for the campus wide loop.  We also "polish" both loops to 1 meg-ohm so that we have a "high resistance" in the RF cooling circuits.
>> 
>> Dennis Schweiger
>> University of Mighigan/LNF
>> 
>> 734.647.2055 Ofc
>> 
>> On Fri, Sep 11, 2015 at 3:47 PM, Vito Logiudice <vito.logiudice at uwaterloo.ca<mailto:vito.logiudice at uwaterloo.ca>> wrote:
>> Dear Colleagues,
>> 
>> The process chilled water loop in our cleanroom has consistently oscillated between ~15.4C and ~17.2C over a span of roughly 10 minutes. Our Plant Operations group is looking into the possibility of tightening this up for us by tuning the control sequence. They have asked for guidance on an acceptable specification.
>> 
>> In light of this I would appreciate hearing from you as to your facility's PCW temperature target and tolerance. Thank you much.
>> 
>> Best regards,
>> Vito
>> --
>> Vito Logiudice  P.Eng.
>> Director of Operations, Quantum NanoFab
>> University of Waterloo
>> Lazaridis QNC 1207
>> 200 University Avenue West
>> Waterloo, ON           Canada N2L 3G1
>> Tel.: (519) 888-4567  ext. 38703<tel:%28519%29%20888-4567%20%C2%A0ext.%2038703>
>> Email: vito.logiudice at uwaterloo.ca<mailto:vito.logiudice at uwaterloo.ca>
>> Website: https://fab.qnc.uwaterloo.ca
>> 
>> 
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