New design techniques reduce copper use by 40 percent while decreasing electricity demand and increasing efficiency.
Warmer spring and summer temperatures and rising living standards in developing economies are driving increased worldwide demand for domestic air-conditioning equipment. At the same time, new energy-efficiency standards and changes in regulations to reduce the global-warming impact of refrigerants are forcing major manufacturers of air-conditioning equipment to redesign many of their products to meet new consumer and government expectations. While growth in the air-conditioning market has opened new opportunities, it has also spurred a new wave of innovation.
In the U.S., Friedrich Air Conditioning provides room air conditioners that are installed in windows to offer quick relief from high temperatures and humidity. In these units, a fan blows cold air into the room and exhausts hot air to the outside. Heat exchangers using copper tubes to contain high-pressure refrigerants do the work of making the air cold or hot. Using new technologies, the International Copper Association (ICA) helped to re-engineer the hot air heat exchanger (the condenser) in Friedrich’s window air conditioners to improve efficiency and use less copper tube and aluminum fins, making them lighter and easier to handle.
The new high-performance heat exchanger designs use up to 47 percent less copper, 45 percent less refrigerant and can achieve up to 6 percent better energy efficiency to reduce electricity demand. These improvements are possible by changing the copper tube diameter from 7.94 mm to 5 mm. While this sounds easy, more modification is required beyond a simple diameter change.
Working with engineers from Optimized Thermal Systems, Inc. (OTS) and Friedrich, ICA went deeper into the engineering aspects to evaluate the design. The OTS team notes there are at least three important technical details necessary to accommodate the modification: advanced software simulating how heat exchangers will perform, helical grooves on the inside of small tubes, and an assembly method using pressurized air to expand components into each other.
Advanced heat exchanger design software developed at the University of Maryland’s Center for Environmental Energy Engineering uses “genetic algorithms” to evolve ideal designs. With ICA support, recent enhancements to the software expanded its design capability to include small diameter tubes. The design team determined important operating conditions and manufacturing constraints and then used this software shortcut to explore all design possibilities and their performance, without building any physical components.
Copper is an amazing heat conductor, but using smooth surfaces inside and outside a copper tube is not always good enough for optimal heat transfer. The re-engineered heat exchanger needs a tube with four – five times better heat transfer performance than a smooth tube. The necessary performance is made possible by forming tiny trapezoidal ridges inside the tube and adding precisely engineered fins to the outside.
The final technical detail involves joining the tubes and exterior fins to create an excellent path for heat to flow. The copper tube is inflated into the fins using pressurized air. This precise assembly operation happens in seconds.
Advanced copper-based technologies are enabling innovation in the air-conditioning industry. The same approach taken by Friedrich is being implemented by other major manufacturers worldwide. Hal Stillman, Director of Technology Development and Transfer for the ICA, sums it up: “In an unexpected move, the copper industry is promoting a technology using less copper. This unconventional promotion highlights the industry’s commitment to sustainable development because using less copper, in this case, results in higher efficiency and reduced electricity demand.”
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