HOW DESICCANT 

DEHUMIDIFIERS WORK

Mode of operation 1
Single fan - Built in internal heat recovery

This mode of operation involves only one common fan for both air flows i.e. the process air and reactivation air. In this case, optimal heat recovery can be achieved due to distribution of the air through the purge sector.
This mode of operation, is implemented only in the smallest MDC160/250 desiccant dehumidifiers and in our bespoke range of desiccant air handling units for low dewpoint applications.

The basic principle of rotary desiccant dehumidification technology, is that air is passed through a honey comb desiccant rotor (wheel) that features a large, active dehumidification surface. The rotor is constructed of a fire retardant substrate, impregnated with a high concentration of Silica Gel, resulting in a high adsorption capacity (ability to adsorb water molecules). In this case, the humid process air, passes through 60% of the rotor face area, the exiting process air, is at a much lower moisture content, due to the moisture extracted by the silica gels adsorption process.

In order for this drying process to continue, the extracted moisture is required to be rejected from the rotor, in a separate counter flow airstream. The reactivation airflow, is first past through a small section of the rotor, commonly referred to as the purge sector (heat recovery sector), this preheats the reactivation air, significantly reducing energy consumption, whilst reducing the heat gain in the process sector. Due to the low level of adsorption at high surface temperatures, only a small amount of moisture is adsorbed back into the rotor through this sector.

Once the reactivation air has passed through the purge sector, it is then heated up to a maximum of 140°Cdb, lowering the relative humidity to very low levels. This is then passed through the regeneration zone of the rotor. The high temperature, low relative humidity air, is sufficient to break the molecular bond, between the water vapour and the silica gel. As the moisture is introduced into the air, it results in a warm and humid airflow, that is then exhausted to the outside of the desiccant dehumidifier.

In such way, the desiccant rotor (wheel) continually restores its capacity to adsorb water molecules, from the process airflow. The reactivation airflow, also performs the additional function of cleaning the rotor from contaminants, that could be present on the surface of the rotor. Continuous rotation of the rotor, provides a nonstop process of adsorption/reactivation. Special holding frame from both sides of the desiccant wheel, prevents the mixing of the process air and the reactivation airflows. Moreover, the absence of condensation during the dehumidification process, allows installing the desiccant dehumidifier, without a connection to a drainage system.

Mode of operation 2
Dual fan - External heat recovery option available

This is the most common mode of operation and it allows drying the air very efficiently down to almost 0% RH. This mode of operation is particularly useful in high ambient moisture climates as no moisture is returned to the rotor during the reactivation process.

This mode of operation is implemented from the MDC300 to MDC3000 range of desiccant dehumidifiers.

The basic principle of rotary desiccant dehumidification technology is that air is passed through a honey comb desiccant rotor (wheel) that features a large active dehumidification surface. The rotor is constructed of a fire retardant substrate impregnated with a high concentration of Silica Gel, resulting in a high adsorption capacity (ability to adsorb water molecules). In this case the humid process air passes through 60% of the rotor face area, the exiting process air is at a much lower moisture content due to the moisture extracted by the silica gels adsorption process.

In order for this drying process to continue the extract moisture is required to be rejected from the rotor in a separate counter flow airstream. The reactivation air is heated up to a maximum of 140°Cdb, lowering the relative humidity to very low levels. This is then passed through the regeneration zone of the rotor. The high temperature low relative humidity air is sufficient to break the molecular bond between the water vapour and the silica gel. As the moisture is introduced into the air it results in a warm and humid airflow that then is exhausted to the outside of the desiccant dehumidifier. In this case an external cross flow heat exchanger can be used to provide heat recovery, the warm humid air is passed through the cross flow heat exchanger, the reactivation airflow in passed through the other path of the heat exchanger recovering heat that would otherwise be lost to external.

In such way, the desiccant rotor (wheel) continually restores its capacity to adsorb water molecules from the process airflow. The reactivation airflow also performs the additional function of cleaning the rotor from contaminants that could be present on the surface of the rotor. Continuous rotation of the rotor provides a nonstop process of adsorption/reactivation. Special holding frame from both sides of the desiccant wheel prevents the mixing of the process air and the reactivation airflows. Moreover, the absence of condensation during the dehumidification process allows installing the desiccant dehumidifier, without a connection to a drainage system.

Mode of operation 3
Dual fan - Built in internal heat recovery

This mode of operation involves a separate fan for both air flows i.e. the process air and reactivation air. In this case optimal heat recovery can be achieved due to distribution of the air through the purge sector.

This mode of operation is available across the DL range, and from the MDC range from the MDC4000 and above.

In this case the desiccant dehumidifier has two separate centrifugal fans for process air and reactivation air intake and exhaust/supply.

The basic principle of rotary desiccant dehumidification technology is that air is passed through a honey comb desiccant rotor (wheel) that features a large active dehumidification surface. The rotor is constructed of a fire retardant substrate impregnated with a high concentration of Silica Gel, resulting in a high adsorption capacity (ability to adsorb water molecules). In this case the humid process air passes through 60% of the rotor face area, the exiting process air is at a much lower moisture content due to the moisture extracted by the silica gels adsorption process.

In order for this drying process to continue the extract moisture is required to be rejected from the rotor in a separate counter flow airstream. The reactivation airflow is first past through a small section of the rotor commonly referred to as the purge sector (heat recovery sector), this preheats the reactivation air, significantly reducing energy consumption whilst reducing the heat gain in the process sector. Due to the low level of adsorption at high surface temperatures only a small amount of moisture is adsorbed back into the rotor through this sector.

Once the reactivation air has passed through the purge sector it is then heated up to a maximum of 140°Cdb, lowering the relative humidity to very low levels. This is then passed through the regeneration zone of the rotor. The high temperature low relative humidity air is sufficient to break the molecular bond between the water vapour and the silica gel. As the moisture is introduced into the air it results in a warm and humid airflow that then is exhausted to the outside of the desiccant dehumidifier.

In such way, the desiccant rotor (wheel) continually restores its capacity to adsorb water molecules from the process airflow. The reactivation airflow also performs the additional function of cleaning the rotor from contaminants that could be present on the surface of the rotor. Continuous rotation of the rotor provides a nonstop process of adsorption/reactivation. Special holding frame from both sides of the desiccant wheel prevents the mixing of the process air and the reactivation airflows. Moreover, the absence of condensation during the dehumidification process allows installing the desiccant dehumidifier, without a connection to a drainage system.

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