Rosahl Membrane Selection
Rosahl membranes are low power dehumidifiers for protecting equipment from moisture damage and condensation. They are for air drying steady-state cabinets and enclosures up to 4m³ or 140 cu ft. Steady-state means at a constant temperature using an airtight enclosure to minimise moisture ingress.
Where cabinets are opened, consider the time needed to reduce the humidity to the set-point. If needed, select a larger membrane to reduce the drying period. The expectation is that cabinets using Rosahl dehumidifiers will remain closed for most of the time. Enclosures larger than 4m³, may need more than one Rosahl membrane.
The precise drying time will depend on several variables, like starting and target humidity, air temperature, volume, and leakage area. The following membrane selection tables give an indication of drying times. We recommend undertaking your own tests.
Economy of selection
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 volume for dehumidifying is smaller. Finally, try and design your application to ensure you are dehumidifying the smallest volume possible.
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Selection
Important: Selecting the Right Size (Avoid Under sizing)
Choosing the correct humidity control solution for your enclosure is critical for reliable performance. A system that is too small may struggle to maintain stable conditions, while one that is too large adds unnecessary cost and complexity. For optimal results, the enclosure should be airtight to the level of a domestic refrigerator and gaps will affect performance. If in doubt use a larger model to avoid disappointment, particularly if seeking a sub 20% RH performance.
Treat humidity control as an engineering decision, rather than simply choosing the lowest-cost option. Relative humidity changes with temperature, so our drying curves assume a constant temperature and an airtight enclosure. Rosahl membranes are rated by applicable volume, but actual humidity levels will vary depending on your specific application.
Selection of membrane by volume and target humidity
Selecting the correct membrane in three steps by using the following table:
- Select the row with your typical ambient humidity from either <70% or <90%
- Select your target humidity and use that column
- Select the next largest sealed enclosure volume that matches your enclosure. And the membrane is on the left
Notes
- If the enclosure is not sealed, use a larger membrane size or improve the sealing.
- This selection table is also for drying 3D print filaments but more on this topic is here: Do Rosahl membranes keep 3D printer filaments dry? – Rosahl
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Drying time curves
The following curves indicate drying performance under defined conditions. The characteristics of the graphs will vary depending on the material in the container and the degree of air-tightness/leakage. If the container contains absorbent material, the membrane induces release of moisture from the material, which may slow dehumidification inside the container. The dehumidifying capacity of the membrane varies according to the absolute water amount inside the container. Changes in the ambient humidity may also affect the performance, and the curves are provided for guidance only.
Typical drying curve for RD3, RD4 & PD3 series
Typical MDL Series drying curve for a 50 litre container at 30°C 90% RH
Typical M-Series drying curve for a 50 litre container at 30°C 90% RH
Important user notes:
Refer to the user manuals in the documentation section of this site. In addition, please note the following points to help you use Rosahl correctly. If you are in any doubt about the suitability of Rosahl for your application, please contact us.
– Rosahl is not intended as a domestic product and is for installation by a qualified person
– Rosahl is for dehumidifying steady-state (sealed) enclosures or cabinets
– The membranes have a half-life of five years’ operating 24/7 at an average annual operating temperature of 18°C. Half-life declines at higher average operating temperatures. When unpowered, the operating life is unaffected by temperature
– You can increase the effective operating life by over-sizing the membrane, using a humidity controller, or operating at lower average temperature
– The device will be effective from -20° to +50°C (the manufacturer has tested it for storage between -40° C up to +80°C).
– When unpowered, the membranes do not provide a barrier to moisture from entering the enclosure.
– The devices require a power supply of 3V DC with constant current-limiting protection. Some fold-back type PSUs are not suitable. All hiccup mode PSUs are unsuitable.
– Power consumption figures are the expected daily average based on our evaluation
– Do not use silicone rubber sealants unless vulcanised by heat curing, as they may damage membrane and performance.
Refer to the FAQ section or contact us for specific applications. For further information see Membrane Selection
Go here for typical Rosahl user guide
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