HUMIDIFICATION & DEHUMIDIFICATION Understanding industrial dehumidification D
Humidity Solutions sales and technical support engineer, Freddy Kar, discuss the different options for dehumidification and the best ways to implement a dehumidification system in different applications
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.
Desiccant vs refrigerant
Fundamentally, there are two different methods of dehumidification. These are desiccant and refrigerant technologies.
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 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. 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 of a refrigerant unit whereas if they are below 15˚C and lower than 50% RH then desiccant technology would be the ideal solution.
Applications
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
32 BUILDING SERVICES & ENVIRONMENTAL ENGINEER JUNE 2024 Read the latest at:
www.bsee.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46
