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The function of a coil in an HVAC setting is to exchange heat from one substance to another, for heating or cooling applications. While the coils often come as part of the package in an HVAC system, there are reasons to evaluate the design of the coils themselves. Coils that are poorly integrated are more likely to use too much energy, decrease airflow, or increase pressure. These effects can lower overall system efficiency and performance. With this guide, HVAC professionals will understand the role that coil selection plays in HVAC system operation.
Factors to Consider in Coil Selection
Coil design comes from various decisions. These factors influence the coil’s ability to perform.
Material
For coil tubes, copper is the standard. Copper carries a number of benefits above other materials, even other metals:
- Copper is highly efficient at transferring heat.
- Copper tubes are unlikely to corrode, unlike iron.
- Coils made of copper may only need a coating to survive high-pressure or chemically aggressive environments.
- Compared to aluminum, copper can handle some humidity.
While aluminum may be the top option for fins, copper offers the greatest long-term performance for coils.
Tube Diameter
Tube diameter selection requires careful consideration. The industry is shifting to the use of smaller diameters as a general option. These tubes allow for higher velocity, which increases the efficiency of heat transfer. With this advantage comes the potential for a sudden decrease in pressure, which can increase fan operation. Larger-diameter tubes are less likely to encounter that pressure drop, but they tend to be less efficient at transferring heat. As such, a just-right size is key to balancing pressure, velocity, and efficiency.
Surface Area
Optimal coil selection usually calls for an increase in surface area. A greater surface area is a key advantage of smaller-diameter tube sizes, but it comes from other design aspects, as well. In general, a higher surface area means that the compressor does not have to work as hard to exchange heat, which can lead to higher output and efficiency. If the compressor has a lighter load, that benefit translates into lower energy consumption and less strain on the equipment over its lifespan.
Tube Layout
Pressure drops are a common problem relating to turbulence, an issue that can be addressed with a proper tube layout. Turbulence comes from uncontrolled airflow across the coils, which leads to pressure drops and other concerns that lower performance and efficiency. Keeping coils shallow encourages consistent airflow, so that the system does not have to work as hard. Using fewer rows of tubes also reduces the amount of turbulence, allowing the system to better regulate changes in pressure.
Fin Spacing
The fins sit next to the coil, dissipating heat as part of the heat exchanging process. The position and layout of the fins affects overall performance of the coils. Fins that are too close together can lower airflow and increase friction, which forces higher operation for effective output. Fins that are further apart make it easy for the air to flow through freely. The trick is to balance the two. Fins with a wavy design increase the ability of the system to control pressure and airflow without compromising operation.
Advantages of Optimal Coil Design
Ultimately, optimal coil design helps to balance the needs of the equipment with the HVAC requirements of the space. The right coil arrangement will have maximum surface area, with a tube diameter that manages pressure and velocity. A heat exchanger coil manufacturer can provide an ideal coil design that maintains control over air pressure, promotes airflow, lowers turbulence, and increases heat exchange rates. With this arrangement, the coils can maintain high levels of output while lowering energy consumption and stress on components.
Choosing the right coils is key for HVAC systems. When the coils are not optimized, they may use more energy than necessary to meet output needs. Poor coil design is associated with increased stress on equipment that leads to expensive repairs or premature replacement. By comparison, optimal coil planning can increase efficiency without compromising output or system performance. Careful coil selection enables HVAC professionals to design systems that meet building requirements efficiently and reliably.
AUTHOR BIO: Jeffrey Sturdivant is the Director of Sales and Engineering for Coilmaster, a U.S.based manufacturer of custom heat exchanger coils, fluid coolers, and condensers used in HVAC, refrigeration, industrial, and OEM applications. He has over 11 years of experience at Coilmaster and focuses on bridging engineering and sales. His oversight ensures that clients receive custom designed coil solutions that meet performance standards, optimizing product specifications, and delivering high quality, reliable heat transfer products with responsive service and technical support.
