Relationship of absolute dehumidifying capacity and ambient

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℃・40％RH

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℃・60％RH

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.

Summary

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

Model	Dehumidifying capacity
PD4, PD5	42 mg/day
PD2, PD3, RD3, RD4	84 mg/day
RS1, RS2	210 mg/day
M-1J1R	1 mg/day
M-2J1R	2 g/day
M-3M1R	2.9 g/day
M-3M1R, MDL-3	4 g/day
M-5J1R, MDL-5, S-5T1	9 g/day
M-7J1R, MDL7, S-7T1	16g /day
M-10J1R, S-10T1	29 g/day

Moisture per cubic metre of air

g/m3 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

50°C 8.3
16.6 24.8 33.1 41.4 49.7 58 66.2 74.5 82.8

45°C 6.5 13.1 19.6 26.1 32.6 39.2 45.7 52.2 58.7 65.3

40°C 5.1 10.2 15.3 20.4 25.5 30.6 35.7 40.8 45.9 51

35°C 4 7.9 11.8 15.8 19.7 23.7 27.6 31.6 35.5 39.5

30°C 3 6.1 9.1 12.1 15.1 18.2 21.2 24.2 27.2 30.3

25°C 2.3 4.6 6.9 9.2 11.5 13.8 16.1 18.4 20.7 23

20°C 1.7 3.5 5.2 6.9 8.6 10.4 12.1 13.8 15.5 17.2

15°C 1.3 2.6 3.8 5.1 6.4 7.7 9 10.2 11.5 12.8

10°C 0.9 1.9 2.8 3.8 4.7 5.6 6.6 7.5 8.4 9.4

5°C 0.7 1.4 2 2.7 3.4 4.1 4.8 5.4 6.1 6.8

0°C 0.5 1 1.5 1.9 2.4 2.9 3.4 3.9 4.4 4.9

-5°C 0.3 0.7 1 1.4 1.7 2.1 2.4 2.7 3.1 3.4

-10°C 0.2 0.5 0.7 1 1.2 1.4 1.7 1.9 2.1 2.4

-15°C 0.2 0.3 0.5 0.6 0.8 1 1.1 1.3 1.5 1.6

-20°C 0.1
0.2 0.3 0.4 0.5 0.7 0.8 0.9 1 1.1