Hot Gas Reheat
Most hot gas reheat and heat reclaim coils are designed with either ½” or 3/8” O.D. tubes. Hot gas reheat coils are typically associated with commercial split systems. The idea is to siphon some of the waste heat off of the system but not enough to allow condensing to occur. Most hot gas reheat coils are only one or two rows deep and are used to slightly reheat the air in humidity control situations. On the other hand, heat reclaim coils are generally considered to be more of a refrigeration system component. The waste heat from compressor racks (from freezers inside a supermarket, for example) can be considerable, and it is not uncommon to have a three, four, or even a six-row coil that will capture this heat. Condensing of the refrigerant (to some degree) inside the coil is typical.
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 frequently 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. Connections are almost universally made from copper.
Keep in mind that although there are a huge variety of material options available for coil designs, unless there is a compelling 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.