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Chilled water is a circulating system that cools by passing through a refrigeration unit to lower its temperature. It is primarily used in central air conditioning systems and industrial applications requiring low-temperature cooling. The chilled water system can be either closed or open, with open systems further classified into spray types. Most central air conditioning systems use closed-loop chilled water, while many industrial plants rely on open systems. Spray-type systems are commonly found in environments where air washing and humidity control are necessary, such as textile mills and electronic manufacturing facilities.
Due to the relatively low temperature of chilled water (typically between 1°C and 20°C, most often between 6°C and 12°C), it creates an ideal environment for bacterial and algal growth. These microorganisms can form biofilms, leading to the proliferation of heterotrophic bacteria, iron bacteria, nitrifying bacteria, and sulfate-reducing bacteria. This can cause corrosion of pipe walls, resulting in rust and reduced heat transfer efficiency in condensers. Additionally, Legionella bacteria may develop in the water, posing serious health risks to humans.
Calcium and magnesium ions in the water can also lead to scale formation when they come into contact with heat exchangers. This scale, mainly composed of calcium carbonate, adheres to the inner walls of copper tubes, reducing heat transfer performance. When combined with dirt and sludge, scaling can worsen corrosion and significantly affect system efficiency. Therefore, the primary goal of chilled water treatment is to prevent or minimize scale, corrosion, and biological fouling.
Compared to cooling water, chilled water has distinct characteristics. The volume of water stored and circulated is generally smaller. The temperature remains relatively stable, and the concentration factor typically stays constant. In closed-loop systems, there is no evaporation, so water loss is minimal. In open systems, only a small portion is exposed to air, resulting in negligible water loss. In spray systems, especially during summer, some water is absorbed by the air, which may slightly reduce the ion concentration. However, due to the small variation in concentration, it is considered nearly constant.
Water treatment chemicals are usually applied once and need to remain effective over a specific cycle. Corrosion in chilled water systems is a major issue, often leading to red water caused by the oxidation of ferrous hydroxide into reddish-brown rust. In open and spray systems, oxygen levels are higher due to exposure to air, while closed systems experience rapid oxygen depletion, leading to different corrosion behaviors.
Corrosion inhibitors can be inorganic or organic, including chromates, nitrites, silicates, phosphonates, and polymers like polyaspartic acid. Scale inhibitors help prevent the deposition of inorganic salts on metal surfaces, ensuring efficient heat transfer. Anti-fouling agents are formulated with epoxy resins and amino resins, mixed with anti-corrosion additives. They offer excellent protection against rust, good thermal conductivity, and resistance to weak acids and solvents. The coating formed is dense, flexible, and durable, providing long-term equipment protection.