This calculator, currently at a very early stage of development , will predict the dehumidification capacity needed for a museum store or archive whose climate is controlled by dehumidification alone, with a freely wandering temperature, heavily buffered by the ground beneath.

Enter the outside monthly average temperature in ℃ and RH % in the first two columns.
The default outside values are for Birmingham UK

In the third column enter the predicted inside temperature obtained from a thermal modelling program. The default values are typical for an insulated building over earth, with some internal heat generation.

In the fourth column enter the desired inside RH for each month.

Since there is no possibility for humidification, the predicted RH may be less than intended but will never be above the set value.

The value for buffer capacity is in kg/m3 of active cellulose, which is considered to be the outer 20 mm of the paper edges exposed directly to the room air. The calculation of the buffered RH is very approximate, given the month time between calculations. Please suggest a good algorithm for this!

Outside climate Inside climate
MonthTRH T RH set RH pred. kWh/m3

Air changes per hour:  
Buffer capacity in (kg of active cellulose)/m3:    

Annual energy for dehumidification (kWh/m3)

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kWh: for dehumidification ——
Temperature: out ——  in ——
RH: out ——  in ——

This calculation includes the effect of humidity buffering but it is a very crude approximation, because of the long calculation interval. The predicted RH values below the set point are therefore pessimistic.
There is no correction for the efficiency of the dehumidifier. The calculation is based on the latent heat of condensation of water vapour.
In a humidity buffered building there is no need for continuous dehumidification. Therefore, the energy use is averaged to kWh per month, on the assumption that intermittent solar power will be used.

Description of the calculation

© Tim Padfield 2015
Creative Commons License
This work is licensed under a
Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 Unported License.

This calculator is in JavaScript. It can be saved to disk and will work offline.