Desiccant dehumidification units

Studies conducted over the last few decades have shown that active humidity control is required in modern, sealed buildings. These studies investigated humidity control using cooling coils [direct expansion (DX) or chilled water], desiccant dehumidification units, mechanical ventilation devices, and humidification units. Additionally, the use of hygroscopically active materials (such as plaster, brick, and ceramic) to control the relative humidity of the surfaces has been considered. This topic is divided into three sections— cooling coil units, desiccant dehumidification devices, and hygroscopically active materials. 

Desiccant dehumidification units are available with both solid and liquid desiccants. The difference between solid and liquid desiccants is their reaction to moisture. Some simply collect moisture like a sponge collects water. These desiccants are called adsorbents and are mostly solid materials. Silica gel is an example of a solid adsorbent. Other desiccants undergo a chemical or physical change as they collect moisture. These are called absorbents and are usually liquids or solids that become liquid as they absorb moisture. Lithium... 

Humidity control may be accomplished by using cooling coil units, desiccant dehumidification units, and hygroscopically active materials. Effects of most indoor air pollutants are strongly influenced by the... 

In summer the ventilation air has to be dehumidified to keep the required comfort and to prevent from condensation at cold ceilings. The air dehumidification is done by a liquid desiccant dehumidification and cooling system, sketched in Figure 271. Warm and humid outside air is cooled and dried in a special dehumidifier by a concentrated Lithium Chloride salt solution (LiCl-H20) before it is blown into the atrium of the building. From there several air handling units draw the air into the offices and provide additional cooling on demand. 

Membranes are used to dehydrate process air streams as replacement for desiccant dryers or adsorption systems. Such membrane units have been on the market for many years, but they are mainly for small gas streams. The manbranes being used have very high water to air selectivity. The dehumidification units are usually connected to a compressed air line, and loss of pressurized air through the membrane may be a major cost. 

The dehumidification rate for the Prototype Unit was measured and compared with an unmodified dehumidifier. The Prototype Unit and dehumidifier appliance were placed in a 60 m2 room with open windows. The test was conducted at an ambient temperature of 23 °C and relative humidity of 80 %. The amount of water collected after 8 h was weighed and dehumidification rates of 0.14 Kg/h and 0.13 Kg/h were obtained for the Prototype Unit and unmodified dehumidifier, respectively. This indicates that coating the formulated catalysts onto the desiccant wheel does not significantly affect its dehumidification function. 

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