Dehumidification Systems
Humidity is the water vapour carried by air. In combating humidity, it is necessary to understand the definitions of absolute humidity and relative humidity and to evaluate them on the basis of psychrometry.
The mass quantity of water vapour carried in 1 m³ of air is defined as absolute humidity, while the maximum amount of water vapour it can carry is defined as the saturation point. Relative humidity is the ratio of the existing moisture in the air under certain conditions to the maximum moisture it will carry under those conditions.
Psychrometry is the science of humid air. Psychrometry addresses the amount of water vapour in the air and examines its thermodynamic properties such as temperature, pressure, humidity and enthalpy. The psychrometric diagram is prepared depending on the altitude from sea level, which is accepted as the atmospheric pressure of the region in which it is used.
In industrial facilities and all material warehouses, humidity control is of great importance to protect materials and prevent damage such as mould and corrosion. The requirement in creating suitable climate conditions is generally the relative humidity value.
The main objective is to maintain relative humidity at a certain level regardless of the ambient temperature. Examples of storage and manufacturing area humidity conditions for some general applications are given below.
• Metal materials 45%
• Electronic goods 40%
• Pharmaceutical manufacturing 5-45%
• Military ammunition storage 45%
Dehumidification Systems
When designing dehumidification systems, it is possible to view the properties of the air such as moisture content, enthalpy (heat change of the system under constant pressure), dry and wet bulb temperatures, relative humidity on the psychrometric diagram, calculate the dew point, and graphically view data on the psychrometric diagram such as condensation and latent heat processes.Dehumidification by Cooling on Cold Surfaces
If air is cooled below its dew point, its moisture-holding capacity decreases and the water vapour in the air begins to condense and separates as water. Thus, excess moisture in the cooled air is removed and reheated to the ambient air temperature before being supplied to the space. These types of systems are generally defined as compressor-based dehumidification systems incorporating refrigeration cycles. All equipment of the cooling cycle is designed to be included within the system. The air passing through the evaporator is cooled below the dew point, the air's moisture is removed, and the dry bulb temperature is increased by passing through the condenser. In this way, the relative humidity and absolute humidity of the process air can be reduced. This dehumidification system is suitable for applications with high relative humidity ratio and dry bulb temperature. It is not suitable for use in cold climates with high humidity ratios.Desiccant-Evaporative Dehumidification Systems (Absorption Dehumidification)
The main operation in desiccant dehumidification is that water vapour molecules contained in humid air are retained in the labyrinths of carrier materials (adsorbents), and dried air is supplied to the space. Silica gel is generally used as the desiccant material. Rotors filled with silica gel are used in absorption dehumidification units. The rotor fill divided into two sections rotates at a speed between 5 - 25 revolutions per hour. 75% of the rotor fill is used for moisture retention and transport (adsorption), while the other 25% is used for the release of captured moisture (desorption). The continuous rotation of the rotor ensures the continuity of the dehumidification process and the achievement of the desired humidity level. Water molecules trapped in the silica gel labyrinths in the rotor evaporate with the hot air blown in the discharge section. Dehumidification systems created with the desiccant method can be used in humid and hot climate conditions as well as in humid and cold climate conditions. Through this feature, it provides application flexibility advantages compared to cold surface dehumidification systems. Çiğdem Arslan - Project and Sales Director / Project and Sales Director - RolaxAdvertisement
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