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Subject:
From:
Joyce Koo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 8 Mar 2017 15:36:29 -0500
Content-Type:
text/plain
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thx.  (it only goes for 40-60%).
> I've used Aprilaire ducted dehumidifiers. Pricey but nice clean hookup,
> and we had no issues with them. When you see the pricing, you will
> probably end up going with just increasing global warming with reheaters
> instead!
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Chuck Brummer
> Sent: Wednesday, March 08, 2017 8:53 AM
> To: [log in to unmask]
> Subject: Re: [TN] humidity control
>
> Oh Boy,
>
> How high are the ceilings?  What are the walls finished with?  Luckily the
> room is not that large.
>
> Your right, humidification will not be that difficult.  Dehumidification,
> much harder and your local HVAC guy has no idea.
> You need an air handler to get enough air into your room to make it
> positive pressure.  You need a large enough compressor to cool air moving
> faster than typical over the coils.
> You need a reheat unit to warm the air moving through the coils when you
> have not met your RH requirement.  Typically you have two compressor
> systems so that on runs 24/7 and the other comes on and off on demand.
> Your RH requirement is much lower than ours is so your compressors will
> run often.  I have a +/- 4% spec and we can hold that at a target of 48%.
> Find a cleanroom designer to spec your system for the HVAC contractor.
>
>
>
> Chuck Brummer
> Medical Flex, EMSD
> 8357 Canoga Ave, Canoga Park, CA 91304-2605
> Office: +1 818 734-4930 | Mobile: +1 805 890-8452 [log in to unmask]
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
> Sent: Wednesday, March 08, 2017 6:14 AM
> To: [log in to unmask]
> Subject: [EXTERNAL] Re: [TN] humidity control
>
> Hi Joyce-
>
> Doesn't exist.
>
> Humidification is easier than de-humidification but is still problematic
> because boiling water is a violent process at the molecular level and can
> be corrosive.
>
> Properly conditioned air is a very precious and expensive commodity. The
> first rule is that you have to treat it that way: You need to know how
> much air is leaking out so you know how much capacity you need for
> humidification/de-humidification. If you use robots in a sealed plastic
> bag you will still need to provide a little make-up air to keep positive
> pressure in the clean room. But add people and they put out humidity too!
> And they consume oxygen so a certain amount of "fresh" input air is
> required. A U.S. standard for HVAC is 20CFM/operator, which seems quite
> high unless these operators are doing very hard physical labor.
>
> On many cleanrooms, the HVAC contractor had no business designing the
> system because they have no experience with the practicalities of the
> velocities and pressures involved. They try to get by with a standard
> rooftop commercial HVAC unit of higher capacity to get the number of air
> changes per hour up to the requirements of the cleanliness level. When you
> really start treating air as a precious commodity you will find these
> commercial units are basically un-sealed (partially because the
> differential pressures involved in the cleanroom are larger than what they
> designed their little weather strip seals for.
>
> I had pretty good luck using the area above the cleanroom ceiling as a
> simple mixing plenum: A standard rooftop HVAC unit, sized appropriately
> for the load (not oversized like most commercial buildings), kept the
> plenum at the required temperature and supplied the required make-up air.
> A separate loop went through the de-humidifiers (ducted) and the HEPAs
> were just self-powered. The humidifier was just one of the wall mount
> units like many SMT areas have. If you have designed properly than you
> shouldn't need to put a heater in the system to get the air conditioner in
> the HVAC unit to act like a dehumidifier--the solution most commercial
> HVAC designers will try to sell you on.
>
> But even with the degree of control I had, 30-34% is too tight a range to
> be practically feasible. I was happy with being able to maintain a 10%
> range. And that's near the low side. If needed in the spring when
> temperatures are moderate, then it may be unavoidable to use a re-heater.
> You don't provide a temperature range, but if you can tolerate swings in
> that then I can see 30-34% being achievable by increasing/decreasing
> temperature in addition to the other controls.
>
> By the way, this is a control system, so it is not difficult to get it to
> go unstable. One cleanroom I oversaw would have swings of 50%RH within 10
> minutes!
>
> Wayne
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
> Sent: Wednesday, March 08, 2017 5:43 AM
> To: [log in to unmask]
> Subject: [TN] humidity control
>
> Guys and Gals,
> Does anyone know a unit (reasonably priced and compact) to control
> temperature at 21 C+/- 2 C and RH (I know it is hard one) at 30-34%
> capable of constant maintaining within the range?  The canadian
> winter/spring is crazy, especially for the RH.. we can swing from extreme
> dry to rain within few hours.  I know majority of control are for (1)
> office - not going to work (2) electronic cleanroom - >40% RH... but I do
> need 30-34% RH to get laser working.  Many thanks.
> regards,
>                       jk (already got 4 dehumidifier in the room of size
> of 29'x12') 3M security scanners have not detected
> any malicious content in this message.
>
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>

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