As the industry shifts towards smaller-diameter tubing to improve heat transfer in heat exchangers,...
A Comparative Study of Small-Diameter Copper Tubes with LU-VE
With growing concerns about environmental sustainability and energy efficiency, reducing refrigerant charge has become a paramount objective for Original Equipment Manufacturers (OEMs), engineers, and designers in the HVAC/R sector.
The efficiency and effectiveness of heat exchangers are heavily dependent on selecting appropriate components, including tubing materials and designs. Engineers must balance heat transfer efficiency, pressure drop, cost-effectiveness, and durability when designing heat exchangers for HVAC/R systems. Among the crucial decisions to make is the choice between small-diameter copper tubes and aluminum microchannel tubes, offering distinct advantages and challenges.
Optimizing Tubing Material for Reduced Refrigerant Charge
A critical consideration for OEMs to consider is which tubing material is better suited for designing heat exchanger components that reduce refrigerant charge.
LU-VE, a heat exchanger manufacturer based in Italy, sought to reduce the volume of the tubes and the internal coil condenser components to minimize refrigerant charge. Reducing internal volume promotes refrigerant efficiency, improved system performance, and energy efficiency. 
A smaller internal volume means less space for the refrigerant within the condenser. Condenser efficiency is closely linked to the volume of refrigerant it contains. By reducing the volume, manufacturers can minimize the refrigerant required to operate the system effectively. Reducing refrigerant charge is particularly important in light of environmental concerns regarding the leakage and emission of refrigerants, many of which have high global warming potential (GWP) and contribute to climate change.
Additionally, a smaller internal volume can improve the overall performance of the HVAC/R system. With less refrigerant circulating through the system, there may be reduced pressure drop and more efficient heat transfer within the condenser, leading to improved system performance and reliability.
Small-Diameter Copper Tubes in Heat Exchanger Design
In pursuit of an optimal solution, LU-VE, in partnership with Optimized Thermal Systems, R & D (OTS R&D), explored various design configurations, including tube diameter and material composition modifications. LU-VE's comparative analysis included three scenarios: a baseline design with three-eighths-inch copper tubes, a copper tube design with a five-millimeter diameter, and an all-aluminum microchannel heat exchanger. The goal was to maintain equivalent capacity while minimizing internal volume, ultimately reducing the refrigerant charge.
The results, small-diameter copper tubes present inherent advantages over competing microchannel tubes, presenting OEMs, engineers, and designers with a compelling solution for minimizing the internal volume of condenser components. Furthermore, these small-diameter copper tubes offer a significant edge in reducing system refrigerant volume. The reduced internal volume of the coils demands less refrigerant for charging, resulting in additional benefits in system design, including a notable reduction in overall system weight.
The Impact of Component Interconnectedness and Performance on Material Selection
In their comparative analysis, LU-VE scrutinized two distinct metrics. Initially, their focus honed in on the tube volume, representing the core of the heat exchanger. Transitioning from the baseline three-eighths inch outer diameter copper tubes to the five-millimeter design, LU-VE observed a reduction in tube volume. The shift yielded a sixty percent reduction in the internal volume. However, the all-aluminum microchannel counterpart reduced the internal volume by three percent more than the five-millimeter design.
Expanding their analysis to encompass the condenser’s components, including headers, LU-VE uncovered further insights into the efficacy of their design modifications. While the microchannel design initially appeared marginally advantageous in tube volume reduction, accounting for the headers reshaped the narrative. Due to its mechanical construction, the aluminum microchannel in a parallel flow arrangement requires relatively large headers to accommodate the aluminum profile entering the header. According to LU-VE’s research, a minimum header diameter of 38mm is required to get proper performance from a condenser.
The five-millimeter copper tube design reduced the internal volume by approximately fifty percent compared to the baseline and emerged as the more competitive option than the microchannel configuration.
This comprehensive perspective underscores the interconnectedness of condenser components and highlights the importance of considering the system as a cohesive unit to achieve a cost-effective solution for regulatory compliance.
If you want to learn more about Designing for the New Refrigerants, you can access the entire webinar with Cara Martin, COO of OTS R&D, Inc., here.
