Coil Glossary of Terms

June 18, 2024

For those who are new to the world of commercial/industrial heating and cooling coils – or for anyone who wants a quick review of the common terms used in our industry – we’ve put together this handy list of terms and brief definitions. It’s a quick and easy way to get conversational in the language of coils!

AHRI Certified Coils: Fluid, steam or refrigerant coils that have been tested for performance of operational conditions by an independent third-party laboratory, in accordance with the Air-Conditioning, Heating and Refrigeration Institute (AHRI).

Airtight Housings: Used in industrial process heating and cooling, these coil housings allow heat transfer while preventing the cross contamination of process air and ambient air.

Brazing: The process of joining copper tubes by using a torch to melt braze filler metal (higher strength and performance than solder) around the joint, forming a leak-free connection.

Casing: The frame of a coil – typically made of galvanized steel, as well as other metals – which holds the tubing and fins in place, providing structural support, stability and resistance to mechanical stresses.

Chilled Water Coil: A type of cooling coil that uses chilled water as the cooling medium.

Cleanable Coils: Fluid coils that feature removable plugs on the return bends, allowing access to the interior of the coil for cleaning.

Coil Coating: Coatings applied to the coil surface to enhance corrosion resistance, increase “wetting”, prolonging the lifespan of the coil, especially in highly corrosive environments.

Condensate: Water formed when water vapor in warm air comes in contact with the cool surfaces of a coil and converts to liquid form (the condensation process).

Condensate Drain Pan: A tray located beneath the cooling coil that collects condensed water and directs it away from the HVAC system to prevent damage and microbial growth. Having a properly sloped drain pan can have a dramatic effect on Indoor Air Quality (IAQ).

Condenser Coil: A component of a cooling system that uses refrigerant to absorb heat from indoor air and transfers it to the outdoor environment.

Cooling Coil: A component of an HVAC system that removes heat from the air by transferring it to water, refrigerant or another fluid and moving it to the outdoor environment.

Dampered Face and Bypass Coil (also known as Integral Face and Bypass Coil): A coil designed to preheat and temper incoming air in cold temperatures, while minimizing the possibility of coil freezing.

Dew Point: The temperature at which a water vapor in the air begins, or would begin, to condense into water.

Direct Expansion (DX) Coil: Also known as an evaporator coil, the coil in a cooling system that facilitates the transfer of heat from indoor air to the refrigerant, thus cooling the air.

Distributing Steam Coil: A steam coil with smaller-diameter tubes inside larger tubes, which distribute the steam uniformly across the coil. This minimizes the possibility of freezing, which is why it is sometimes referred to as a “freeze proof coil”.

Evaporator Coil: Also known as a direct expansion (DX) coil, the coil in a cooling system that facilitates the transfer of heat from indoor air to the refrigerant, thus cooling the air.

Expansion Valve: A device that regulates the flow of refrigerant into the evaporator coil, controlling the temperature and pressure of the refrigerant to achieve the desired cooling effect.

Fins: Thin metal plates or sheets (typically aluminum) which the coil tubes pass through and connect to, increasing the surface area available for heat transfer.

Hairpins: Long tubes (typically copper) which are bent before being laced through the coil fins, reducing the number of brazed joints.

Headers: Manifold-like structures at the inlet and outlet of the coil where the heating or cooling medium enters and exits.

Heat Exchanger: Another name for a coil, any device that transfers heat from one source, such as a fluid, to another source, such as air.

Heating Coil: A component of an HVAC system that utilizes steam or hot water flowing through the metal tubes to transfer heat to the air.

Hot Water Coil: A type of heating coil that uses hot water as the heating medium.

Humidity Control Coil: Designed for hospitals and other applications where excess moisture can accumulate and damage expensive HEPA and ULPA filters, this type of cooling coil recirculates the warm fluid leaving the coil to heat and desaturate the air exiting the coil. Sometimes called a “de-sat coil”.

Industrial Process Coil (or Process Coil): A heavy-duty coil used specifically to heat or cool air for an industrial process, often in extreme environments.

Integral Face and Bypass Coil (IFB Coil): Also known as a Dampered Face and Bypass Coil, it is designed to preheat and temper incoming air in cold temperatures, while minimizing the possibility of coil freezing.

Refrigerant: A substance used in HVAC systems to absorb and transfer heat, undergoing phase changes from liquid to gas, then back to liquid again to accomplish cooling or heating.

Refrigerant Coil: An evaporator coil (DX coil) or condenser coil which uses refrigerant as the heat transfer medium.

Return Bend: A semicircular fitting used to connect two tubes at the end of a coil, typically by brazing.

Split Core Coils: Coils built specifically to be divided into smaller sections that can be re-assembled on-site in order to ease installation in applications with limited space.

Steam Coil: A heating coil that utilizes steam as a heat source.

Straight-Through Steam Coils: Steam coils with a continuous straight-through steam path, with opposite end supply and condensate headers.

Subcooling: The process of lowering the temperature of a liquid refrigerant below its saturation temperature to improve system efficiency and performance, often achieved in the condenser coil.

Superheat: The temperature increase of a vapor refrigerant above its saturation temperature at a given pressure, typically occurring in the evaporator coil, ensuring that only vapor enters the compressor.

Tubes/Tubing: Metal (typically copper) tubing that the heat transfer medium flows through inside a coil to achieve heating or cooling.

Tube Expansion: The process during coil production where the tubes are expanded into the fins, creating a mechanical bond that allows maximum heat transfer.

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