Selecting the correct membrane

Translation

ROSAHL was developed for dehumidifying (air drying) steady state cabinets up to 2m³ or 70 cu ft in size.  This means the cabinets should be sealed to avoid the ingress of moisture under normal operation-in the same ways as a refrigerator.  It is understood that the cabinet will be opened from time to time to rearrange items but the expectation is that it will be closed most of the time.  For enclosures larger than 2m³ multiple Rosahl membranes are used.

The precise drying time will depends on a number of variables such as starting and target humidity, air temperature, volume, leakage and so on.  The following tables have been prepared to give users an indication of drying times.  We recommend you undertake your own tests.  If you are interested in scientific models for estimating drying times use the contact us section to obtain the relevant links.

 

Selection

We provide a number of graphs and tables to aid selection of the correct Rosahl element.  They are provided for guidance only as every application is different. See notes on humidity

ROSAHL’s dehumidifying capacity (cabinet internal humidity) is determined from the volume of air in the cabinet and its humidity.  From the graph below, select a suitable model from the intersection of the required humidity and volume.  For example, if your cabinet has a volume of 0.5m³ and your target humidity is 50% then select the MDL-5 or equivalent.  This table is based on a surrounding humidity of 90% and may be adjusted for higher/lower levels.  Contact us for further information.

Rosahl has a half-life of about six years when operated 24/7.  This is extended when operating time for shorter periods ot time.  We recommend over-sizing the membrane where practicable to allow for a decline in performance over time.

Economy of selection

For different enclosure sizes we recommend different models or Rosahl.  If the initial drying time is not critical, and the enclosure remains closed for the majority of time, or you have a lower starting humidity, it is often possible to use a smaller membrane.

It is also important to consider the volume of air inside the enclosure rather than the external dimension.  For example if your enclosure is 50% full by volume of non porous material, then the space to be dehumidified will be reduce by a similar amount.

 

Selection of membrane by volume and target humidity

Rosal selection 1 1024x422 Selecting the correct membrane

 

Catalogue selection chart for Rosahl membranes only

 

Rosahl membrane only (no power supply or humidity controller)

Model No. RP1/RP3 RD3/RD4 MDL-3 MDL-5 MDL-7
Dehumidifying (g/day) 0.084 0.084 4 8 16
Applicable volume m³ *1 <0.002 <0.002 <0.5 <1 <2
Element Terminal Voltage                                             3VDC
Power Consumption (W) *2 0.08 0.08 2 3 4
Dimensions (mm) Ø17×11*3 30x24x5.5 96x63x2.3 96x88x2.3 116x108x2.3
Weight (g) 1.8 1.8 20 25 50
Operating temperature (°C)                                             -10 to +50

 

Notes: *1 Assumes sealed state enclosure. *2 Average power consumption over a year. *3 M12 x P0.5 thread

 

Drying curves

The following graphs provide an indication of drying performance under different conditions.  The characteristics of the graphs may vary depending on the material in the container and the degree of air-tightness.  If the container contains absorbent material the membrane induces release of moisture from the material, which may slow de-humidification inside the container.  The dehumidifying capacity of the membrane varies according to the absolute water amount inside the container.

 

 Typical drying curve for RD & PD series

Rosal selection 4 Selecting the correct membrane

 

 

Typical drying performance for a 50 litre container

Rosal selection 2 Selecting the correct membrane

 

Typical drying performance for the MDL-5 membrane

Rosal selection 3 Selecting the correct membrane