[Nhcoll-l] Humidity in collection rooms

[Callomon,Paul]

In our experience a recurring problem in wet collection environments is the combination of ambient high humidity and lower-than-ambient temperature. The dew point – the temperature at which water vapor condenses – is a function of both factors; with ambient humidity but below-ambient temperatures, such as in a room that has air cooling but no humidity control, condensation happens when it would not if the temperature was also ambient.

Water will condense onto the coldest surface first, which tends to be the glass bottle surface. Room dehumidifiers exploit this effect by cooling a coil with refrigerant gas to present an even colder surface on which condensation will thus happen first. Purpose-built fluid storage rooms often have an air drier that removes vapor from the incoming air before it is cooled, thus providing both humidity and temperature control.

Many years ago we constructed an entire building thus equipped, but the cost of running and maintaining the driers got them switched off, with disastrous consequences that have taken decades to remediate. The entire building quickly became a mold farm and rust was rampant even in recently-installed racking. Because the building had been designed as a sealed system, there were no windows to open to at least mitigate the worst effects.

If you have high ambient humidity that cannot be lowered, therefore, it might be safest not to cool the room much. This is suboptimal in conservation terms, but the consequences of lowering the dew point are rust, mold and other undesirable results of liquid condensation running down your jars and over your racks.


Paul Callomon
Collection Manager, Malacology and General Invertebrates
________________________________
Academy of Natural Sciences of Drexel University
1900 Benjamin Franklin Parkway, Philadelphia PA 19103-1195, USA
prc44 at drexel.edu<mailto:prc44 at drexel.edu> Tel 215-405-5096 - Fax 215-299-1170



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