Chilled Water Coils
Most chilled water coils are designed with either 1/2” or 5/8” O.D. tubes. However, there are an increasing number of manufacturers who design chilled water coils with 3/8” tubes, especially for coils that are for very low capacity (5 tons or less). Larger tubes are typically used because they keep the water pressure drop lower. However, the smaller tonnage coils usually have short tube lengths and, thus, inherently lower fluid pressure drops.
The most commonly used tube material is copper, and there are a variety of tube wall thickness options to handle different applications. Aluminum is the most commonly used material for the fins on a coil, because of good heat transfer characteristics and low cost. There are many different fin designs that will either enhance heat transfer or reduce air pressure drop, depending on the requirement. Coil frames (or casings, flanges, whatever you might call them) are normally galvanized, but stainless steel is a good consideration to increase the longevity of the coil. Coil connections are typically copper, brass, or steel.
Keep in mind that although there is a huge variety of material options available for coil designs, unless there is a design reason to specify something special, most coils will be purchased based on the cost alone, so using the “standard” coil material is generally the approach to take. We are strong believers in stainless steel frames for cooling coils, assuming that there is condensation resulting from the cooling process (which is not always the case in dry climates).