HUMIDIFICATION & DEHUMIDIFICATION


Understanding industrial


Simon Marshall


Business development manager at Humidity Solutions


humiditysolutions.co.uk D


ehumidification in industrial applications can take many forms in both the application and the equipment used.


Uses can range from small-scale clinic rooms to close control battery manufacture, steelworks, or storage of valuable artefacts. In this article, we’ll discuss the different options for dehumidification and the best ways to implement a dehumidification system in different applications. Fundamentally, there are two


different methods of dehumidification: desiccant and refrigerant technologies.


Desiccant units Desiccant dehumidification is the process of chemically removing moisture from the air and is widely used in industry. Desiccant units utilise a high surface area rotor which is covered in silica that air is passed through. The silica, which is full of small holes


further increases the surface area and will adsorb the moisture from the air as the H2O molecules bind to the Si in the rotor. This is done in what we call the ‘process airflow’. The rotor then slowly turns as the second stage of the process begins. In this stage, about ¼ of the rotor is heated to around 125°C and the water is evaporated from the rotor and sent into the atmosphere via ‘regeneration air’. The dry process air delivers the dehumidification, and the regeneration air is purely to remove water from the rotor. In the majority of industrial applications, these two airflows are separated, however, for smaller uses, three port units can be used which merge the inlet for the process and regeneration airflows. The main benefit of using desiccant dehumidification is that it is effective down to low temperatures (as low as -20˚C) and can dry to very low relative humidity (RH) levels. This makes it


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dehumidification


What is the best way to remove moisture from an industrial environment? Simon Marshall discusses the options available and their suitability for different applications.


ideal for use in the process industry and cold stores. However, it is always important to note that the adsorption process will generate heat. Generally, you can expect to see a heat gain of 15-30°C across the rotor, although this can be counteracted with the use of pre or post-cooling.


Refrigeration systems Refrigerant units rely on the removal of moisture from the air by passing it over a cooling coil. This relies on the coil temperature being lower than the dew point of the air passing over it. The dew point is the point on the psychrometric chart at which the air cannot hold any more water, as it is already at 100% relative humidity. To explain this in simple terms,


when your house is at normal room temperature at 50-60% RH and you bring a drink from the fridge it will usually ‘sweat’. This is because the air around the bottle will be at 4°C which is well below the dew point of the air inside the house and so the air will release its moisture as condensation on the surface of the bottle. A refrigerant dehumidifier uses the same principle, as this change in temperature across the coil causes the moisture that is being passed over to condense. Whilst the water removed is taken away as a liquid via a drain connection, the remaining airflow is now dehumidified and put back into the space. Refrigerant technology is most effective when the conditions are warm and humid, making them perfect for use in a swimming pool or spa room where humidity is often at 30°C and 80% RH. When the temperature decreases, the dehumidification process becomes less effective as the delta temperature difference between the coil and the air reduces. Away from swimming pools, typical usage of a refrigerant dehumidifier would be for general comfort and storage applications or where humidity does not need to be below 50% RH and is a heated space in winter.


As a rule of thumb, if the required


conditions are above 15°C and 50% RH then you would typically make use


Desiccant installed as an in-room solution


Desiccant installed as part of an HVAC system


A refrigerant dehumidifier serving a commercial swimming pool


of a refrigerant unit whereas if they are below 15°C and lower than 50% RH then desiccant technology would be the ideal solution.


Air movement There are two different approaches to providing dehumidification for spaces. These are via ductwork or air handling unit or an in-room solution. When approaching a new project, one of the best ways of providing dehumidification is via the existing ductwork system as it provides good distribution of conditioned air. This typically means placing a desiccant dehumidifier on an airflow into a room and used in conjunction with an existing air handling unit, matching the air volume with the fans in the dehumidifier. In a system which uses recirculation air, a good approach is to place the dehumidifier downstream of the AHU and use the dehumidifier to provide air into the room at the correct humidity level.


When using this approach, it is


important to note the heat gain across the rotor, as this can cause issues with temperature control when the air reaches the room. This can be counteracted by the use of a post cooling coil which will typically use a chilled water circuit to counteract the heat gain from the main dehumidifier unit. Alternatively, you can use in-room air conditioning to ensure that the air entering the room is at the correct


temperature. In a total loss system, however, the loads are typically higher than that of a recirculation system so a different approach can be taken. In this scenario, a dehumidifier can be used before the air reaches the AHU, pre-treating the air to a set absolute humidity value. However, as a result of the larger loads, a pre-cooling coil often proves useful. This pre-cooling coil acts as a refrigerant dehumidifier before the air reaches the desiccant rotor which can sometimes double the total capacity of a system. Following the dehumidifier, the AHU


can manage the temperature control, but this must be accounted for when sizing the AHU cooling capacity. To achieve the correct humidity, you must control the absolute humidity level which should be set to the room’s set point. In-room solutions are better when there is no external HVAC system bringing in large amounts of conditioned fresh air. Sometimes it can also be logistically challenging to tap into existing ductwork, so an in-room solution can often be more suitable. When sizing this equipment the key thing to consider is air infiltration as this will be a significant portion of the load that is brought on the system to maintain the set point. Air is typically distributed using ductwork in the space and the humidity is controlled with an in-room sensor. ■


EIBI | JULY � AUGUST 2025


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