Methods to stabilize and maintain extremely low humidity in a lab environment

My atomic physics lab is in a building that experiences huge swings in humidity levels during the year due to the monsoon season

Our building provides temperature, but not humidity control. Using just the building temperature control results in the following lab climates:

10 months out of the year, the room is at

T $\approx 24.4 ^oC$

Relative Humidity $< 10\%$

2 months out of the year, the lab is at

T $\approx 24.4^oC$

Relative Humidity $\approx 50\%$

This season variation necessitates significant recalibration twice per year at the beginning and end of the monsoon season. The sensitive components are mainly opto-mechanical.

The lab currently has a dehumidifier that is spec'd at 45 pints per day during the wet season. This specification indicates how much water the unit will remove from the air in a given day when the air is saturated with water (100% relative humidity). The problem with such a specification is that 100% relative humidity is a way different environment than 40% or 50% humidity.

On a wet day, this unit reduces the lab relative humidity by about 10% from 55% to 45%. This is still far from the lab's climate most of the year. It is a trade off, though, because it will also raise the lab temperature by about 1 degree C, which necessitates other recalibration. I am investigating options to further reduce the humidity.

The lab is approximately 5 meters X 10 meters X 3 meters in size. Most of the experiment is on a very full optics table that is 1.5 meters X 4 meters. There are lots of cables and water tubing that require access to the table, making climate isolation of the table difficult (although not impossible).

A few options under consideration are the following:

1: Introduce an additional higher capacity dehumidifier

Pros:

• Fast and easy implementation

Cons:

• it is unknown how efficient a dehumidifier will function when the relative humidity is only 45%.

• Manufacturers do not specify how well the unit will work at low humidity levels, only at 80% +.

2: Fill sensitive areas with positive pressure Nitrogen

Pros:

• Excellent climate control
• Minimal impact on room temperature

Cons:

• requires significant reconfiguration of experimental setup.
• Requires refilling Nitrogen tank frequently, a recurring cost.

3: Isolate experiment from lab climate using large plastic enclosures and recirculate air in this enclosure

Pros:

• Excellent environment isolation

Cons:

• requires significant reconfiguration of laboratory and would likely restrict access to areas of the experiment.
• It could also likely result in a temperature increase of the experiment area.

Introducing an additional room dehumidifier would be the easiest option by far.

So my Question is: does anyone know how efficient dehumidifiers works in dry environments? E.g., if I were to purchase an additional dehumidifier, would could I achieve a humidity level of less than 30% or does the humidity level asymptote off at some level due to a limit on the efficiency of dehumidifiers?

I realize an alternative would be to humidify the lab 10 months out of the year. However, having low humidity is extremely convenient for rapidly water-cooling components. During our wet season, our water-cooling results in considerable condensation on our components.

-
Chalk up to the list of Nitrogen's cons: danger to life and limb in case of a leak. –  Deer Hunter Jun 27 '13 at 20:41
Joe - check out Chapter 23 of ASHRAE's HVAC Systems and Equipment Handbook (2008). –  Deer Hunter Jun 27 '13 at 20:46
I found an interesting external link: Desiccant Dehumidification vs. Mechanical Refrigeration ( bry-air.com/… ) In summary, their recommendation is that desiccant based dehumidifiers are necessary if you need relative humidity levels between 1% and 45% –  Joe Jun 27 '13 at 22:20
Maybe you could use slightly warmer cooling water to prevent condensation? Are you using open-cycle cooling - slightly wasteful. –  akrasia Aug 14 '14 at 13:18

One option: Buy more dehumidifiers, and a space heater. Use the space heater to maintain the lab at the "elevated" temperature when the humidity is low and the dehumidifiers are not running.

Another option: Run your dehumidifier when the humidity is high, but run a humidifier when the humidity is low. Meet in the middle.

Yet another option: Build a tent around your optics table and control the climate in there. Less air volume means less challenge. The tent probably doesn't have to be completely airtight.

-

It is probably not an answer good enough, but I try. My experiences with a small commercial dehumidifier were great when humidity was 100%. I tested it long term at 60% without big effect.

I was trying to decrease humidity with Calcium Chloride type material and ventilator (Silica gel is probably safer but less efficient), it worked better but 10%, I have never seen. But maybe with a lot of material... Actually I am impressed that you have 10%, even your presence must influence it...

-