Dehumidifiers are essential in many residential and commercial settings to improve the quality of air, to prevent growth and mildew, and to slow down the corrosion of different materials. There are several different mechanisms by which they remove moisture from the air, but the most common among them are refrigerant and chemical methods. The refrigerant dehumidifiers cool down the air to convert the moisture to liquid form, which is then collected in a container. These dehumidifiers are quite effective and energy efficient. The downside is that they require greater maintenance and they cannot work at low temperatures which make them unsuitable for several industrial purposes. On the other hand, chemical dehumidifiers work using desiccant materials to remove moisture from the air. They are indispensible for usage at low temperatures because they do not rely on condensation. Here are details on the working and design of these absorbent dehumidifiers.
How is the Air Dried?
Like refrigerant dehumidifiers, chemical dehumidifiers make use of one or two fans to draw the moist air in. It is then passed over a slowly rotating wheel which is impregnated with the desiccant material. The wheel typically consists of closely spaced sheets of metal which are deposited with desiccant material on both sides. The air channels through the slit in the wheel and passes over the desiccant crystals. These crystals, usually silica gel, have exceptional affinity to water and absorb the moisture from the air as it passes over it. Some chemical dehumidifiers work using liquid desiccant system like flowing lithium chloride solution which absorbs moisture from the air. The dried air is then returned to the room lowering the overall humidity in it. Using these systems humidity levels of between 0 and 50% can be achieved; one can control the level using a humidistat often provided with the appliance.
Where Does The Collected Moisture Go?
The desiccant crystal or liquid which has absorbed water lose their ability to store any more moisture. Therefore, there is a limit to the amount of moisture they can store. However, these materials have a highly convenient property that if they are heated the absorbed moisture is released regenerating them. As a result, Chemical dehumidifiers can work continuously without any effort from the user.
Typically, in the dry units as the moist air from the room moves in, a small amount of air are forced into the regeneration chamber where it is heated using either direct burner fire or hot water or steam coils. This high temperature stream of air is then passed over the wheel and the moisture is driven out of the crystals. This wet and hot air is then released into the environs of the area being dried. In case of liquid desiccant systems the diluter lithium chloride solution is passed over a gas burned heater. The solution is then reused for further absorption.
Chemical dehumidifiers work on the basis of these simple principles, but they are extremely effective for many industrial and commercial applications, especially the ones that require subzero temperature capability.