Coil Selection: More Than Meets the Eye
Whether designing a new system, performing a 1/1 coil replacement, or upgrading a coil to improve equipment performance, many factors are involved in choosing the proper coil. Not only are there various coil types – chilled water, hot water, DX evaporator, standard steam, steam distributing, etc. – there are numerous materials, dimensions, water and air velocities, and configurations that must be determined when making a coil selection. Replacing an existing coil with an identical one is not necessarily the most suitable choice, as there may be a number of ways to improve performance or lengthen lifespan of the coil and related equipment. This is where a highly-experienced HVAC contractor like PJM steps in, as choosing the most suitable and efficient coil is an involved process.
The first step in selecting a coil is to determine its configuration, which includes coil face area, number of rows of tubes, tube diameter, number of fins and fin surface design, coil circuiting, and whether turbulators are required. Construction options must be chosen as well – tube material and wall thickness, fin material and thickness, casing material, header type and material, and optional coatings. Operating conditions and environment are factored into the various calculations to arrive at the optimal coil for the application. Thicker, heavier tubes translate into longer coil life, and stainless steel casings can be used where corrosion is a concern. Materials used for tubes and fins (copper, cupro-nickel, aluminum, stainless steel, etc.) should be selected according to the environment to prolong life, and surface coatings can be added to prevent corrosion.
Air velocity, water velocity, and moisture carryover are also important considerations when choosing a coil. Proper coil circuiting is necessary to ensure the correct fluid velocity to prevent fouling and poor heat transfer in the event of velocities that are too low, and tube erosion due to velocities that are too high. Low air velocity can result in hot and cold spots in leaving-air temperatures, and too-high air velocity leads to excessive noise, high pressure drop, and increased risk of moisture carryover. Carryover, which occurs when water droplets are blown off the fins into the unit, is also influenced by fin spacing, materials, and configuration as well as tube spacing and coil face height.
There are numerous coil selection computer programs available, and most manufacturers also offer their own software to aid in sizing and calculations, but there are still many variables that require the expertise of an HVAC contractor like PJM Mechanical. For more information on coil selection and installation, please call PJM Service Department manager Ricky Folk at 609-921-1394.
PJM Mechanical Contractors, Inc. is a multi-faceted mechanical contractor providing construction and installation, service and maintenance, and design/build services in a comprehensive range of mechanical disciplines that include HVAC, plumbing, controls, refrigeration, custom metal fabrication, piping, fire protection, and backflow preventer testing. PJM primarily serves clients in pharmaceuticals, manufacturing, healthcare, institutional, and other various commercial and industrial sectors.