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RH Calculator

This calculator will predict the RH in a showcase that is fed with a
positive pressure microclimate generator, such as the Mini One. The
formula will calculate final humidity based upon four variables:
. Case Leakage Rate (expressed in Air Changes per Day (ACD))
. Air Supply Rate ( the feed from the microclimate generator, also
expressed in ACD)
. RH of the Air Supply (fed from the microclimate generator)
. RH of the Ambient Air (which surrounds and leaks into the
showcase)

Use this calculator to predict showcase performance as
variables change.
You may use it to predict:
. The volume of air flow you will need to maintain constant
humidity
. How changing the humidity of the input will affect your showcase
humidity
. The effects of ambient humidity variations on your showcase
. How well sealed your showcase must be to use a microclimate
generator with a known output
. The maximum showcase volume that can be conditioned on a known
input

For example:
To calculate how a well-sealed, 5 cubic meter / 150 cubic foot showcase
with a target humidity of 50% would respond to a moderately dry gallery
when treated by a Mini One Microclimate Generator (output of 24
cubic meters per day), input:
. Case Leakage Rate: estimated as 1 ACD
. Air supply rate: 4.8 ACD (derived by dividing the Mini One's 24
cubic meter daily output by 5 the showcase's 5 cubic meter volume)
. Air Supply RH: 50% (as set on the Mini One controller)
. Ambient RH: 38% (as measured in the gallery)

If the above data are entered into the calculator, the resulting
predicted showcase RH will be 47.9 % RH. If the predicted humidity level
is not acceptable, you may wish to better seal the case, increase the
air supply (if possible), or increase the humidity of the air supply.

During periods of extreme ambient humidity the calculator may also be
used to calculate a temporary RH input to compensate on a seasonal
basis. For example, changing only the Air Supply RH in the example above
to 52.5% will raise the resulting humidity in the showcase to 50% RH.

NOTE: To change calculations, hit the "Reset Calculator" button.

Case Leakage Rate (ACD)
Air Supply Rate (ACD)
Supply/Leakage Ratio
Air Supply RH
Ambient RH
 
Resulting Case RH
 

The Excel version of this calculation is easier to work with, especially when testing for changing variables. Click here to download an Excel file.