i was afraid someone going to say that... the only one i can see is the
two duck system with one with 100% RH (bucket water saturated) and other
goes to the external air, control unit to mix the two inlet to get RH in
the range... pricy and big.. not for small room like ours.
crying... thanks Wayne.
         jk
> 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')
>