The decarbonization of the HVAC/R industry was on full display at the 2023 AHR Expo in Atlanta, with many manufacturers opting to showcase the increased efficiency of heating and cooling appliances and equipment. This is largely because legislators worldwide have set net-zero targets for the carbon dioxide (CO2) expelled into the atmosphere.
While there are several strategies to achieve low- to zero-carbon emissions, such as safer refrigerant management practices, efficient refrigeration and HVAC systems are essential to energy management and the operational cost of residential, commercial, or industrial buildings.
The energy efficiency of heating and cooling appliances and equipment has steadily increased in recent years, partly thanks to the use of smaller-diameter copper tubes in heat pumps, air conditioners and refrigeration systems.
This year, heat pumps dominated the scene at AHR with various low ambient temperature capabilities and capacities. Our team observed that many heat pumps have copper tubes in their heat exchangers: some ⅜-inch (9.5mm), but mostly 7mm in diameter, depending on the unit capacity.
Additionally, manufacturers are designing a new generation of heat exchangers with more advantages over present designs. These new heat exchangers have copper tubing designed with an even smaller diameter (5mm copper tube) than competing heat exchanger designs, allowing for a better-performing product with higher internal and external heat transfer coefficients.
That said, understanding the beneficial properties of small-diameter copper tubes is more important than ever, especially with the new HVAC and appliance equipment designed for green buildings and better efficiency.
For a comprehensive overview, watch this webinar presented by Optimized Thermal Solutions (OTS), which covers small-diameter tube fundamentals, heat exchanger design challenges and considerations, accessible and inexpensive design tools, example cases, and more.
Copper is known for its superior thermal conductivity, approximately 400W/m.K. This high thermal conductivity ensures low thermal resistance in the wall of the tube, which facilitates heat transfer between the inner and outer surfaces. When a fluid flows through the tube, the heat is transferred from the fluid to the tube wall due to the temperature difference.
The high thermal conductivity of copper allows for efficient and rapid heat transfer, ensuring that the temperature of the fluid is maintained at a constant level. This is particularly important in heat exchanger applications, where the efficient transfer of heat is crucial for the effective functioning of the system.
Overall, the superior thermal conductivity of copper tubes makes them an excellent choice for heat exchangers, offering efficient and effective heat transfer properties.
Copper is a highly durable material with excellent corrosion resistance, making it an ideal choice for heat exchanger tubes. This resistance stems from its ability to form a protective layer of oxide on its surface, which helps to prevent further corrosion.
In addition to corrosion resistance, copper also offers biofouling resistance, which means it is less susceptible to the buildup of organic material on its surface. This is because copper has antimicrobial properties that help to inhibit the growth of bacteria, fungi, and other microorganisms that can cause biofouling.
From a heat exchanger context, copper reduces material buildup and potential fouling that can prohibit the proper heat transfer within the unit and degrade its performance over time.
The desired temper for ductility of copper tubes offers several manufacturing advantages for heat exchanger applications. One of the most significant is the ability to achieve the precise temper of copper, allowing for inner grooving maximization, which can improve the heat transfer properties of the tube.
Inner grooving improves the heat transfer properties of the tube by creating turbulence within the flow of fluid.
This, in turn, enhances heat transfer by increasing the surface area of the tube that is in contact with the fluid. This means that more heat can be transferred from the fluid to the tube, improving the overall efficiency of the heat exchanger.
The predictable temper and material characteristics of copper also make it easier to bend and shape the tubes, which can be useful in applications where space is limited or where complex shapes are required.
Overall, the predictability and pliability of copper tubes make them an excellent choice for heat exchangers, offering superior heat transfer properties and ease of use during manufacturing.
Small-diameter copper tubes have superior strength, allowing thinner walls. This means that the tubes can have a smaller diameter, while maintaining the same strength level as larger tubes with thicker walls.
Additionally, smaller diameter tubes can be used to create heat exchangers with a more compact design, which can be useful in applications where space is limited.
Small-diameter copper tube offers the ability to withstand high pressures. This is particularly important for high-pressure systems, such as those using CO2, where the tubes need to be able to withstand significant pressure without compromising performance or safety.
Small-diameter tubes with thinner walls can withstand these high pressures using less material than conventional-diameter tube heat exchangers.
Regarding heat exchanger coils, manufacturing and repair costs are important considerations. Fortunately, using copper tubes in heat exchanger coils can offer significant advantages in both areas.
Round-tube, plate-fin coils made with copper tubes benefit from well-established manufacturing methods that are both efficient and cost-effective.
Additionally, the smaller diameter of copper tubes means less material usage, further reducing manufacturing costs.
Smaller diameter coils made with copper tubes can be produced using familiar tube-handling and coil-assembly equipment, keeping manufacturing costs low. In terms of longevity and durability, copper is a superior material that yields products with proven longevity.
Copper's durability also makes it easy to inspect, test, and repair coils, extending their lifespan and reducing repair costs over time. Overall, using copper tubes in heat exchanger coils can offer significant cost savings, while providing superior performance and durability.
Get in touch with the Copper Development Association to partner on the research and development of air-conditioning, refrigeration and heat pump systems and components; in particular, design, analysis, and optimization of tube-fin, small-diameter copper tubes, and brazed plate heat exchangers.