Heat exchangers made with copper tubes are proving to be highly compatible with most of the eco-friendly refrigerants under consideration for refrigeration systems, air conditioners and heat pumps globally, according to the International Copper Association (ICA).
The ICA's Microgroove team leader, Nigel Cotton, said in both laboratory and manufacturing environments, smaller-diameter copper tubes are proving to be a good match for eco-friendly refrigerants.
Candidate refrigerants include Low Global Warming Potential (GWP) hydrofluorocarbons (HFCs) such as HFC-32, which has a GWP of 675; and ultra-low GWP hydrofluoroolefins (HFOs), such as HFO-1234yf and HFO-1234-ze, which have GWPs of 4 and 6, respectively.
Scores of refrigerants that are blends of HFCs are HFOs are also under consideration for various applications. Such refrigerant blends can be tailored to the application by making tradeoffs between performance, cost, GWP and flammability.
“Traditional copper tubes with plate-fins are well suited for these new blends of eco-friendly refrigerants,” Cotton said.
“The use of smaller-diameter tubes further reduces the effective GWP in applications since less refrigerant charge delivers the same capacity.”
Copper also excels when used in heat exchangers for natural refrigerants, including hydrocarbons (e.g., propane, R290) as well as carbon dioxide (R744).
According to the laws of mechanics, the “hoop stress” exerted on a tube decreases with diameter (when pressure and wall thickness are held constant).
Consequently, higher pressures can be applied without increasing the wall thickness or lower wall thicknesses can be used.
“When manufacturers use smaller-diameter copper tube, they can save on materials and increase performance in more ways than one,” Cotton explained.
“The manufacturing infrastructure for supplying evaporators, condensers and gas coolers to the industry has developed to the point where it is available for use.
“For OEMs who want to use smaller diameter copper tubes, the equipment is available.”
High-volume production of MicroGroove coils for residential air-conditioner has been an accomplished fact for more than five years and the successful production of coils for refrigeration systems and commercial applications is ever broadening.
“Equipment today is capable of short runs of specialty products as well as high-volume production. Either can be accomplished with speed and precision,” Cotton said.
Coils for commercial applications typically are not produced in high volumes, so fast-yet-flexible production is paramount, he noted.
Round copper tubes laced through optimized plate fins are the basis for highly efficient evaporators, condensers and gas coolers for countless applications in refrigeration and air conditioning. The ease with which such conventional coils can be made has made them attractive for use for many decades in the past.
The use of smaller diameter tubes with inner grooves allows for even more efficient coils.
“Tube benders, lacers and tube expanders are still at the heart of such production but these steps had to be adapted to smaller tube diameters,” he said.
“The equipment makers responded quickly and admirably so that today a manufacturer can purchase and/or build the equipment necessary to establish a reliable and versatile production line for the manufacturer of coils from smaller diameter copper tubes.”
During a recent webinar sponsored by the Copper Alliance, members of the audience were polled about their greatest concerns about moving to smaller-diameter coil production.
The two biggest concerns were centered around “technology/innovation in this area” and “manufacturing process changes.”
Visit www.microgroove.net or go to ICA at www.copperinfo.com
Meanwhile, the International Copper Association (ICA) and Optimized Thermal Systems (OTS) have announced that newly developed MicroGroove correlations will be implemented in CoilDesigner software.
The software is a proprietary heat exchanger simulation and design optimization tool developed by the Centre for Environmental Energy Engineering (CEEE) at the University of Maryland.
Research at the Shanghai Jiao Tong University (SJTU) resulted in the development of new airside and refrigerant-side correlations, particularly for 5-mm MicroGroove tubes.
To make such correlations readily available to HVAC&R system designers and heat exchanger engineers, the ICA worked with OTS to implement the newly developed correlations into its software design tool.
CoilDesigner is a highly customizable software tool that allows designers to simulate and optimize the performance of heat exchangers.
OTS actively works with various HVAC&R designers around the globe to optimize heat exchanger geometry, including investigation of the use of small diameter tubes.
For information on CoilDesigner, visit www.ceee.umd.edu.