Bigger is not always better, and one recent example is the new MicroGroove technology, which was introduced in 2010. This technology is defined by smaller diameter copper tubing with enhanced inner surfaces for the purpose of reducing refrigerant charge, minimizing material content and improving heat transfer. Higher density refrigerants that require less volume for a given heat exchange, or hydrocarbons (where refrigerant quantity is limited), are the key applications for this technology.

The MicroGroove brand is supported and presented by the International Copper Association (ICA). ICA recently published a press release touting the advantages of MicroGroove over microchannel aluminum.

According to the ICA, the advantages include increases in heat transfer without added costs and risks of aluminum brazing, easier drainage of moisture from evaporator coils, more durability and corrosion resistance, and smaller volumes of refrigerant necessary to pass through the tubing.

Nigel Cotton, ICA OEM team leader, explained the reasons for developing MicroGroove technology. “The industry has been under pressure to develop new products as a result of new drivers on the market,” he said. “First was a need for higher energy efficiency, second was a change of refrigerant, third was a continuous cost pressure. By introducing smaller diameter copper tubes, the copper industry could offer cost-reduction options that are based on higher heat transfer, reduced refrigerant charge, and lower material usage.”

Residential and Commercial Applications

An added advantage to MicroGroove technology is its adaptability to HVACR equipment in both the residential and commercial markets. Wenson Zheng, ICA deputy director of technology, explained its uses.

“We started developing applications with some of the leading air-conditioning manufacturers and they wanted to start with residential air conditioners,” he said. “In terms of units, residential air conditioners account for more 90 percent of the market for air conditioning products.

“Currently widespread uptake is seen in room air conditioning with further uptake in some larger units. MicroGroove is available for use in condensers, evaporators, heat pumps, chillers, and heat exchangers, big and small.

“But MicroGroove is suitable for commercial applications, too. Some manufacturers are already developing commercial-sized applications, and we see this as an area of interest going forward.”

Dave Hawkes, senior manager, systems engineering, Tecumseh Products Co., also believes there are several applications for this technology. “To date, R-410A has been the refrigerant of choice for air conditioning applications, replacing R-22,” he said. “So, the resulting benefits have been better realized for residential air conditioning. It really comes down to economics; however, this technology should migrate to commercial refrigeration in time.

“There are certainly possibilities going forward, as hydrocarbons are gaining interest, and will require less internal volume and lower system charge levels, or high-pressure refrigerants like R-744 that require components with a higher burst pressure rating.”

Offshoots of Downsizing

Perhaps the key description in explaining this technology is “micro.” A small tube has several different ramifications. The reduction in copper tube size leads to an increase in the local heat transfer coefficient, which describes the heat exchanged between the refrigerant and the inside wall of the tube. In simple terms, more refrigerant comes into closer contact with the copper so heat is transferred more quickly.

Cotton explained how smaller tubes affect their burst strength. “The tube can withstand higher pressures as the diameter is reduced,” he said. “In other words, the burst strength goes up. Higher pressures can be used inside the tube, allowing for greater heat transfer.”

Hawkes said there are a number of parameters that affect heat exchanger performance. “One of these is the surface area to volume ratio of the tube,” he said. “Smaller diameter tubes provide a greater surface area to volume ratio along with improved heat transfer. Resulting heat exchanger performance, however, will also be dependent on the refrigerant’s properties.”

Smaller diameter tubes can be used in evaporator and condenser coils. “Due to the higher pressure drop that can be allowed in the high side of the system, its application to condenser coils should be more prevalent,” Hawkes said. “There are benefits to be gained in both evaporator and condenser, but the greatest gain in performance is on the condenser side.”

Going small will likely result in smaller products, too, according to Cotton and Hawkes. “We see that some air conditioning manufacturers are able to make the units smaller and reduce material use in the materials and not just in copper,” said Cotton. “New designs are meeting performance targets with less aluminum fin material and less refrigerant as well as less copper tube material.”

Hawkes said, “The smaller tube diameter can also reduce the overall size of the coil, as the ratio of surface area of the fins relative to the tube diameter (for optimal heat exchange) will stay somewhat constant.”

Hawkes noted that MicroGroove technology also has an impact on refrigerant choices. “R-410A emerging as the preferred replacement for R-22 in air conditioning applications was a leader in driving the trend to smaller tube diameters,” he said. “As the industry was predominantly tooled for larger tube and fin coils, the initial product offering for R-410A was not achieving optimal performance. As these features have been optimized, the theoretical advantages of the refrigerant can be realized.”

Cotton said that ICA expects new refrigerants to enter the market, but for the time being the copper tubes will work with a variety of different refrigerants. “In China, MicroGroove has been tested with propane [R-290] and is proving to be very successful, especially since the refrigerant volume is reduced,” he said. “For those who wish to use carbon dioxide [R-744] as a refrigerant, MicroGroove is a possible choice.”

The new technology will also benefit HVACR contractors, too. “The contractor benefits from a dependable unit with known components with which he or she is familiar for installation or maintenance,” said Cotton. “The end user benefits from higher energy efficiency, a smaller unit and, in general, a greener product due to the efficient use of resources.”

Package size and refrigerant choice make MicroGroove technology an appealing look for HVACR contractors, according to Hawkes. “There is lower cost and lower refrigerant charge,” he said. “The potential of reducing coil size can reduce the overall package size and weight, helping the contractor with handling and stocking. The end user benefits on efficiency. Both can benefit from less refrigerant charge and material, impacting overall cost.”

Publication date: 6/4/2012