RH Calculator

This Excel calculator makes it easy to 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 The 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.