Attaining High Energy Efficiency with Less Materials Using
Smaller-Diameter, Inner-Grooved Copper Tubes
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Karyer Profits from Widespread Demand for Advanced Heat Exchangers | |
New Coil Designs Reduce Charge and Increase Performance | |
Karyer exhibit at most recent Chillventa. | |
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Karyer is a leading the way in Europe with respect to the design of advanced heat exchangers. A decade ago its engineers realized that “business as usual” would not lead to long-term success. Its customers were moving forward with radically new designs of heat exchangers. Familiar tube-fin technology was rapidly evolving toward the use of 5 mm diameter copper tubes. To stand out from the competition, Karyer would need to change its basis of operation.
Even seven millimeter diameter tubes were becoming obsolete for some applications. As a result, Karyer expanded its coil manufacturing in 7 mm, 8 mm, 3/8 in., 1/2 in. and 5/8 in. geometries with the addition of 5 mm geometries.
The advantages were undeniable. It was clear that 5 mm geometries could be used in products that would be more efficient, compact and economical. The company started designing coils with 5 mm inner-grooved copper tubes, while keeping up with product innovations and not forgetting its responsibility towards nature and green sustainability.
The advantages of using these 5 mm MicroGroove tubes generally could be listed as follows:
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- High unit capacity and outstanding performance and efficiency.
- Compactness in designs and dimensional reduction of products.
- Lower installation areas or volumes.
- Less unit weight (since thinner tubes result in lighter coils).
- Lower unit prices.
- Smaller size and less weight reduce material costs.
- Lower internal volume results in less refrigerant charge.
- Ideal for flammable refrigerants such as R290 and R600a.
- Environment-friendly with energy and material savings.
- Improvements in COP, SEER and EER ratings.
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The features that lead to the above advantages can be summarized as follows:
Inner Grooves: Tubes with inner grooves are now widely available from tube suppliers. The inner grooves perfectly complement the smaller diameter. Compared to the laminar flow of refrigerant as it passes through a tube with smooth inside walls, inner grooved tube walls generate turbulence in the refrigerant flow. As a result, the boundary layers on the inner surface of smooth tubes are disrupted and more heat is transferred from the refrigerant to the tube wall. This increase in the heat transfer coefficient (HTC) increases the heat-transfer capacity of the heat exchanger.
Less Weight: Coils made with 5 mm MicroGroove tubes typically can be made around 40 percent lighter than coils made with 7 mm tubes for equivalent OEM products. In other words, the usage of 5 mm tubes positively affects the total weight, compactness and cost of the appliance or equipment.
Higher Surface-to-Volume Ratio: Inside the tube, the ratio of surface area to the volume is greater for 5 mm tubes than for 7 mm tubes. This surface-to-volume ratio nearly doubles for 5 mm tubes compared to 7 mm tubes.
Thinner Walls: At the same working pressures, thinner walls can be used in 5 mm tubes. As a result of these dimensional effects, not only does heat transfer increase but also cost decreases due to less material usage.
Less Refrigerant: Likewise, the refrigerant volume typically can be reduced by about 40 percent in terms of the internal volume of the coils, which is reflected also in the refrigerant charge. As new refrigerants appear in the market and become dominant, the decrease in internal volume makes it easier and cheaper to adopt innovative refrigerants, including natural refrigerants and refrigerant blends. Heat exchangers made with smaller-diameter tubes are ideal for use with flammable refrigerants for which there may be charge-use restrictions.
Price/Capacity: For equivalent designs, a price increase of 10 to 15 percent is expected as the diameter increases from 5 mm to 7 mm.
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Four Prototypical Product Applications
The advantages are plain to see in four representative case studies:
1. An ice making machine (R290);
2. A complete line of bottle coolers (R290);
3. A heat pump evaporator (R32); and
4. A monoblock condenser for a heat pump (R290).
These case studies typify the 5 mm coil requests received and manufactured by Karyer in the recent past. Application requests involving natural refrigerants have been increasing dramatically in recent years. Three of the four requests described here use propane (290) as a refrigerant. R290 is a flammable refrigerant so there are often constraints placed on the amount of charge that can be used in a single refrigerant circuit, especially for indoor applications.
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Case 1: Ice Making Machine
The first request was from an industrial ice machine manufacturer who wanted to switch to R290 in its condensers. The existing design used R134a with a 7 mm geometry.
The challenge for Karyer was to re-design the heat exchangers for R290, maximizing capacity within similar dimensions and using similar fans. It was known that 5 mm geometries with grooved tubes could deliver high performance within limited volumes. In the final condenser designs, capacities from 300 W to 1500 W were achieved from a heat transfer surface area of just 0.5 to 4.5 m2 with 5 mm geometries.
Chart 1-1 compares the new design with the existing designs in terms of capacity versus the external surface area of the product. In addition to obtaining the same cooling with final designs, the outer dimensions are preserved and internal volumes of refrigerant were greatly decreased.
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Chart 1-1 Capacity vs. Surface Area | |
Case 1: Condenser for an ice making machine (R290) | |
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Case 2: Bottle Coolers
The next request originated from a bottle cooler producer who wanted to use R290 as a refrigerant and develop a whole new catalog of products that use this new refrigerant. As in the previous example, the challenge was to maximize capacity within the constraints of existing product dimensions and fans. The target capacities were between 0.75 kW and 3.50 kW at 15 K temperature differences. The new designs use 5 mm geometries at the preferred air velocity ranges, which were between 1.75 and 2.25 m/s using existing fan models. The capacities using grooved tubes were 10 percent higher for inner-grooved tubes compared to the smooth tubes. (See Chart 2-1.)
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Chart 2-1 Capacity Comparison of Grooved & Smooth Tubes | |
Case-2: Heat exchangers for a complete line of bottle coolers (R290). | |
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Case 3: A Heat Pump Evaporator
The third request was for direct expansion (DX) evaporators for heat pump units. A DX coil allows condensed liquid to expand within the coil and pick up heat from the environment. Indoors DX coils cool the indoor spaces. Outdoors, DX coils pick up heat to be later released for space or water heating.
The DX coil project compared 5 mm and 7 mm geometries. First a comparison was made with grooved tubes in both cases. The objective was to achieve the highest efficiency within the 600 mm x 900 mm dimensions. Capacities and unit prices were calculated for products with 5 mm and 7 mm tube geometries. The calculations were run using a 6 K temperature difference with R32 refrigerant.
Considering the very limited available depth (around 100 mm) narrower geometries are chosen. Every design was optimized for the tube diameter selection. The 5 mm tube geometry was more advantageous than the 7 mm tube design. Furthermore, the airside pressure drop was less for smaller tube diameters. Hence the 5 mm geometry increases the capacity of this product. (See Chart 3-1.)
Next, the 5 mm smooth tube was compared with the 5 mm grooved tube. The price/capacity index clearly shows that the 5 mm MicroGroove product design is ahead of others. (See Chart 3-2.)
The efficiency improved by 10 to 20 percent with 5 mm geometry compared to the 7 mm geometry. The refrigerant charge is also reduced by the choosing 5 mm MicroGroove.
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Chart 3-1 Air Side Pressure Drop for 5 mm & 7 mm | |
Chart 3-2 Price/capacity Chart | |
Case-3: A heat pump evaporator (R32). | |
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Case 4: A Monoblock Condenser for a Heat Pump
The fourth request was for a monoblock condenser unit. Designs with 5 mm grooved tubes were compared with designs with 7 mm grooved tubes in 300 mm x 300 mm and 500 mm x 500 mm dimensions. The design criteria include a 13 K temperature difference with R290 refrigerant.
In this study, designs were optimized for the two different tube geometries. The advantage of 5 mm MicroGroove tubes easily can be seen in the price versus capacity chart. (See Chart 4-1.)
An optimized 5 mm smooth tube design was added for comparison with the optimized grooved designs. (See Chart 4-2.) The airside pressure drop was reduced with the less costly option, i.e., the 5 mm grooved tube design.
Chart 4-3 compares internal volume differences in products with the same tube length. Reduction in tube diameter results in reduced internal volume for the the same tube length, which lowers the refrigerant charge.
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Chart 4-1 Optimization with 5 mm | |
Chart 4-2 Price/capacity Chart | |
Chart 4-3 Less Volume, Less Refrigerant | Case-4: A monoblock condenser for a heat pump (R290). | |
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Success and Expansion
According to Hagop Kartun, Technical Coordinator at Karyer, the company set a goal to become one of the leading heat exchanger coil manufacturer in the world. Its strategy consists of working closely with its customers to provide custom solutions to them, using the most advanced technologies available.
“Karyer’s focus on RTPF allows Karyer to develop a versatile portfolio of advanced heat exchangers and manufacturing capability," said Mr. Kartun. “In the past decade, the leadership at Karyer recognized the unique advantages of smaller diameter copper tubes for the air conditioners, heat pumps and refrigeration equipment.
“Our engineers realized early on that the smaller-diameter copper tubes could provide higher efficiency for heat exchangers across a wide range of sizes and applications,” he continued.
As Karyer’s OEM customers expressed interest in RTPF technology for next generation applications, Karyer engineers focused on advancing the technology along with its manufacturing capacity. The company would expand into a 55,000 square meter establishment and increase its workforce to 600 employees.
Karyer faces competition from major European coil makers in its quest to become one of the top coil makers in the world. (See Table 1 in the main article of MicroGroove Update Volume 12, Number 2A.)
The challenge for Karyer has been not only to design a new generation of heat exchangers but also to manufacture them in volume. A Karyer video gives a peek inside its production facility and shows the production equipment that is used in the construction of advanced RTPF coils, including fin-stamping, interlacing of tubes through the fin plates, brazing of copper tube circuitry and other production processes.
The company is well on its way to attaining that goal.
Karyer Promotional Video
https://youtu.be/3SsZiq1IMRo
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Extra Case-3 Photographs: Direct Exchange (DX) Monoblock Evaporator Coil (5 mm). | |
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Advanced Technologies and Versatile Products
A wide range of copper-tube sizes and internal enhancements are available from Karyer to provide a high level of performance. An array of coatings is also available to provide a suitable level of corrosion protection.
The range of heat exchanger designs is impressive. Product categories include OEM heat exchangers, unit coolers, commercial evaporators, commercial condensers, industrial condensers, CO2 evaporators and gas coolers, dry coolers, oil coolers, and heat recovery heat exchangers. Individual catalogues are available for each of these product categories as well as a general product catalogue.
https://karyergroup.com/en/downloads/product-catalogues
Capacities of the commercial condensers listed in Karyer’s General Catalogue range from 0.5 kW to 250 kW, for example. From the Heat Exchanger Product catalogue, tube diameters for this type of product are 5 mm, 7 mm, 5/16”, 3/8”, 1/2”, and 5/8”. Evaporator and condenser coils have been designed for hydrocarbon refrigerants (R290 and R600a) as well as carbon dioxide refrigerant (R744) with suitable design pressure and strength.
Karyer offers fin designs with flat, corrugated and louvered fins. For fin materials, customers can specify copper, marine alloy, hydrophilic, hydrophobic, gold epoxy, and other coatings.
In other words, Karyer has ample manufacturing capability, so customers can specify fins, tubes and coil designs optimized to their applications. Karyer offers product selection software to its customers, including web versions and desktop versions.
https://karyergroup.com/en/softwares
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Extra Case-4 Photographs: Manufactured MicroGroove condenser coil (5 mm). | |
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Beyond the Pandemic
Karyer was affected by the global pandemic as much as any manufacturer. The company resumed its participation at trade shows in 2022, beginning with Mostra Convegno Expocomfort (MCE). Karyer had a similar booth at Chillventa.
Short Video of the Karyer exhibit at the 2022 MCE.
https://youtu.be/L5nd20Yva-g
As European OEMs create a new generation of heat pumps, Karyer is reaching its goal of becoming one of the top coil makers in the World. The company is uniquely poised to meet the demand for advanced heat exchanger coils with smaller diameter copper tubes, which are commonly specified in the latest OEM products. Karyer engineers stand ready to work with OEM heat exchanger engineers, whatever the application, whether commercial or industrial, whether custom or standard, whether high or low volume.
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Acknowledgements
The MicroGroove Update editors would like to thank Hagop Kartun, Technical Coordinator and Manuel Togaç, Marketing Division Manager, both from Karyer, for their cooperation on this "Spotlight" column with a special acknowledgement to Gökhan Güngör, R&D Manager, for information, photographs and charts relating to the case studies presented here.
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New White Paper
Frank Gao. Kerry Song, Yoram Shabtay and Harry Schmitz, "Heat Pumps Deliver High Efficiency Heating" Five Trends in Heat Pump Design for Residential Heating," Appliance and HVAC Report. October 2022.
Digital Issue Download PDF All White Papers
New Technical Publications
Kerry Song, Frank Gao, Yoram Shabtay "Design of 5 mm Copper Tube Heat Exchangers for Display Cabinets with R404A" Proceedings of 19th International Refrigeration and Air Conditioning Conference. Purdue University, West Lafayette, Indiana, Paper 331.
Yoram Shabtay, Frank Gao, Kerry Song, "Simulation of the effects of copper tube diameter on refrigerant charge reduction in split AC systems and refrigerated cabinets" TPTPR, 2021 6th IIR Thermophysical properties and Transfer Processes of Refrigerants Conference (Virtual) Sept., 2021, Paper 1969.
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