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Introduction to using a membrane dehumidifier

Rosahl is a compact membrane dehumidifier for use in closed cabinets. It uses a solid polymer membrane that ejects moisture when a low voltage electrical charge is applied. It is a compact, low-power, maintenance-free way of drying and has numerous advantages over alternative methods. The membrane dehumidifier is suitable for use between -10 and 50°C and up to 90% RH.

A Rosahl membrane dehumidifier is designed for a steady state conditions which means the cabinet/enclosure in which they are operating should offer protection against the ingress of moisture under normal operating conditions.  Typically, cabinets should be sealed to IP52 or NEMA 3 or equivalent.   Rosahl is available in five sizes and four formats for drying enclosure from one litre up to 4m³. Go here for the different models


ROSAHL’s dehumidifying capacity (cabinet internal humidity) is determined from the volume of the cabinet, humidity of the surrounding air, and the target humidity. Go here for more information on membrane selection


ROSAHL works by attracting moist air inside the cabinet to the membrane where the hydrogen and oxygen ions are dissociated by electrolysis.  The hydrogen is migrated through the membrane to recombine on the outside as water vapour.  This requires the ROSAHL dehumidifying element to be mounted on the outside wall of the enclosure to allow venting to take place.  Where the cabinet is outdoors a suitable rainproof cover is needed. Go here for installation information

membrane dehumidifier drying curves

General guideline for using ROSAHL

  • Attach the dehumidifier vertically to the centre of the cabinet’s side wall (do not attach it horizontally to the top or bottom of the cabinet to prevent debris falling on it).
  • When using in an outdoor panel, attach a rain cover and insect-proof net to protect the membrane.
  • A suitable constant current limiting power supply is required
  • Avoid using Rosahl where the humidity generation side (cathode) faces a sealed or poorly ventilated space.
  • Avoid using Rosahl in the presence of volatile anti-corrosion agents or concentrated organic gases are present.
  • Use non-silicon agents if necessary to seal the cabinet
  • If used near fine particles or oil mist, refer to your supplier.
  • Mounting and venting kits are available
Advantages of Rosahl dehumidifiers