Efficient refrigeration and HVAC systems are essential to energy management and the operational cost of residential, commercial, or industrial buildings. An ideal system will conserve energy and limit operational expenses, and the heat exchanger design plays a critical role in the system’s functionality. Manufacturers are designing a new generation of heat exchangers with smaller diameter copper tubes that have advantages over present designs.
The new heat exchangers have copper tubing that is designed with an even smaller diameter than competing heat exchanger designs, allowing for a better performing product with higher internal and external heat transfer coefficients. The copper tubes also offer an inherent material advantage to popular systems in modern HVACR engineering because they are more resistant to corrosion and easier to repair because of heightened flexibility in brazing temperatures.
A number of case studies have been published that support the advantages of smaller diameter copper tubes (≤ 5mm) in heat exchanger designs. Studies on the use of smaller diameter copper tubes in heat exchangers were performed using Multi-Objective Genetic Algorithm(s) (MOGA), an approach that applies the concept of evolution to identify new design configurations. Using a combination of proprietary software tools and software code, the computer simulates thousands of heat exchanger designs, and finds the most optimal points.
Case studies presented at the 2019 ICR included:
- Heat-pump condensers to replace microchannel tubes with smaller diameter copper tubes;
- a window air-conditioner condenser to improve system efficiency while reducing cost and refrigerant charge;
- a refrigerator-freezer condenser to reduce hydrocarbon refrigerant charge;
- the condenser of a packaged terminal A/C system to minimize raw material costs and airside pressure drop while maintaining performance; and
- an evaporator coil for a heat pump water heater to maximize capacity and minimize fan pumping power.
Significant findings of the studies can be narrowed by application, one of which is the use of smaller-diameter tube-fin heat exchangers in PTAC units, which are self-contained heating and air conditioning systems commonly found in hotels, motels, and apartment buildings. Another promising application is in household refrigeration.
MOGA simulations for PTAC systems found that the use of small diameter copper tubes may lead to increased efficiency in heat exchanger design, thus conserving energy and reducing operational costs for the application. In summation, new condenser designs with significant potential to reduce costs and maintain performance were identified. Reductions in airside pressure drop are favorable for noise reduction and material savings, making it possible to develop energy-efficient systems at a low cost. The study indicates a currently-manufactured fin sheet, which provides excellent performance comparable to other optimized designs. This demonstrates manufacturers can achieve high levels of savings using an available fin die.
In refrigeration systems, similar results were found. The optimization study on small diameter copper tube in refrigeration identified several new condenser designs with significant potential to reduce internal volume and maintain performance, thereby reducing total system charge. The study found that given smaller diameter copper tubes (≤ 5mm) reduced the internal tube volume up to 41 percent compared to the baseline design, along with a 57 percent reduction in coil footprint — which allows for a smaller enclosure.
These studies are the starting point for the development of high-performance condenser coils for PTAC and refrigeration applications. The studies adequately demonstrate the benefits of the use of smaller diameter copper tube in HVACR applications, which may lead to increased efficiency and a reduction in energy consumption and operational cost.
Content provided by the Copper Development Association (CDA).
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