[labnetwork] High Humidity Issues in Coastal Areas?

[Paul, Jack]

Hello Kamal,
In general terms, there are only a couple of methods for removing moisture from large volumes of air as required for the cleanroom make-up air.  You can cool the air enough to condense the water vapor out, or you can absorb the water vapor with a dessicant dryer.

Of the two, the most common is to cool the air, since you need to do that anyway. However, to get good condensation the water temperature must be pretty low, and the air velocity through the air handler and over the cooling coils must be relatively slow.  So my best guess is that your infrastructure may be “under designed” to squeeze enough moisture out of the air to reduce the humidity to acceptable levels around 43% or so.  In-line duct dehumidifiers just can’t keep up with the large volumes of air and large quantities of moisture to be taken out of such wet air.

Optimally, you would have one or two large make-up air handlers with large cooling coils (maybe even dual coils in sequence) that would run chilled water provided from your chiller plant (in the building or remote on campus?).  The water temp is low enough (typical design range would be around 5 to 7 deg C) that it would cool the incoming outside air (design conditions maybe 32-37 deg C and 75-100% RH?) to around 13 deg C.  The 13 deg air cannot hold as much water and it condenses out.  This low temperature make-up air is then mixed with recirculated air either in your recirculating air handlers or perhaps within the cleanroom volume if you are using fan-filter units, further reducing the RH as the temperature rises to internal cleanroom design conditions about 20 deg C.  (Since the humidity is “relative” to the capacity of the air to hold water vapor, if the water vapor content remains constant as the temperature rises, the relative humidity decreases as a percentage of capacity).

The other option is dessicant drying, but it consumes very large quantities of energy and actually heats the incoming air, which is in contrast to what you want to accomplish.

Suggest checking your

-        chilled water capacity (how many tons of cooling are available) and the water flow rate

-        chilled water temperature (can it be set lower?)

-        coil size in the make-up air handler- can the air handler be retrofit with a better coil design or in-line dual coils

Hope this helps as a starting point.
Regards,
Jack


From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Kamal Yadav
Sent: Thursday, July 23, 2015 6:42 AM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] High Humidity Issues in Coastal Areas?

Dear All,

During Monsoon time in India, and specially in Mumbai where it rains heavily from June to September, we observe high humidity in the lab ~65%. We have de-humidifiers as well as other HVAC infrastructure. But more control is required. Is it possible or our infrastructure is not good enough?

Are there any other known humidity control solutions known to you. Is it the case with others as well, who are in heavy rains/humid area. This certainly is not the case with Intel in Portland, OR, where it rains a lot too.

--
Thanks,
Kamal Yadav
Sr. Process Technologist
Electrical Engineering
IIT Bombay
Mobile: 7506144798
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