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Is the absolute dehumidifying capacity affected by ambient temperature and humidity?

Rosahl membranes remove moisture from an enclosure. The manufacturer publishes dehumidifying capacity at 30° C and 60% RH as an indication of performance. This is not the absolute dehumidifying capacity of the membrane.

Exactly how much moisture they remove depends on the temperature and absolute humidity (g/m³) in the enclosure. The capacity changes as the moisture in a cabinet changes. The drying curves published by the manufacturer reflect this information.

Drying curves for Rosahl dehumidifying membranes


Absolute dehumidifying capacity

As an example, a size 10 membrane M-10J1R. The published capacity of this device is 29g/day. This assumes ambient conditions of 30° C and 60% RH. Under these conditions, the absolute humidity is 18.21g/m3 (from table below).

The M-10J1R membrane capacity of 29g/day changes as temperature and humidity change as follows:

At 30℃・40RH

Absolute humidity is 12.1g/m3 → 29*(12.1/18.2) =20.2g/day membrane capacity.

At 30℃・90% RH

Absolute humidity is 27.2g/m3 → 29*(27.2/18.2) =44.2g/day membrane capacity.

At 20℃・60RH

Absolute humidity is 10.4g/m3 → 29*(10.4/18.2) =16.6g/day membrane capacity.

At 40℃・60% RH

Absolute humidity is 30.6g/m3 → 29*(30.6/18.2) =48.8g/day membrane capacity.


At 30℃, when RH is higher than 60% the membrane will remove more moisture, and when RH is less than 60% it removes less moisture than the published capacity.

At 60% RH, when temperature is lower than 30° C the membrane removes less moisture, and when temperature is above 30° C it removes more moisture than the published capacity.


Membrane dehumidifying capacities

ModelDehumidifying capacity
PD4, PD542 mg/day
PD2, PD3, RD3, RD484 mg/day
RS1, RS2210 mg/day
M-1J1R1 mg/day
M-2J1R2 g/day
M-3M1R2.9 g/day
M-3M1R, MDL-34 g/day
M-5J1R, MDL-5, S-5T19 g/day
M-7J1R, MDL7, S-7T116g /day
M-10J1R, S-10T129 g/day


Moisture per cubic metre of air