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. > > To report this email as SPAM, please forward it to [log in to unmask] >