Attaining High Energy Efficiency with Less Materials Using
Smaller-Diameter, Inner-Grooved Copper Tubes
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VIRTUAL CONFERENCES FOCUS ON ENERGY EFFICIENT HEATING AND COOLING
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Advanced Technology Lowers the Demand for Energy |
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The energy efficiency of heating and cooling appliances and equipment steadily increased in recent years, partly thanks to the use of smaller diameter copper tubes in heat pumps, air conditioners and refrigeration systems. Efficient appliances and building systems already are helping to draw down greenhouse gas (GHG) emissions and there is still plenty of room for improvement.
Research and development on energy efficiency were presented in 2021 at ACEEE’s Hot Water Forum and the Purdue’s International Refrigeration and Air Conditioning Conference. Both conferences took place virtually this year and high quality presentations and papers were delivered at both.
What follows are some highlights from each of these two conferences, emphasizing the energy efficiency of heating and cooling systems.
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Cheers for HPWHs at Hot Water Forum
The 13th Hot Water Forum featured more than 60 speakers presenting on a wide range of topics. Of course, participants were especially eager to learn about the use of heat pumps water heaters (HPWHs) as a means to fight climate change. Grid decarbonization and electrification of homes and commercial buildings were central to many of the presentations. Emerging HPWH technologies were also discussed, including first looks at models that use low-GWP refrigerants and natural refrigerants.
Indeed, heat pumps for water and space heating represent a tremendous opportunity for “doing more with less.” HPWHs allow for the electrification of water heating, and they are multiple times more efficient than electrical-resistance water heaters. High-efficiency HPWH can play a pivotal role in drawing down GHG emissions from fossil fuels.
The Advanced Water Heating Initiative (AWHI) within the New Buildings Institute made the case for heat pump water heaters. The session titled “All Boats Rise on Heat Pump Water Heaters” included an overview of an advertising campaign that promoted HPWHs in the northwestern region of the United States. The campaign was developed in Partnership with the U.S. Department of Energy to stimulate the market for HPWHs and possibly be adopted by manufacturers and utilities nationally.
“No single region can move the national market on its own, and it will take a concerted and coordinated effort to drive HPWHs into the mainstream.”
Multiple Mode Operation
The session on “Advances in Heat Pump Water Heaters” included a presentation by Greg Pfotenhauer, who is a data scientist from Franklin Energy. Pfotenhauer described experiments on a Rheem HPWH that has three modes of operation, including Heat Pump Only, Energy Saver, and High Demand modes. Pfotenhauer examined usage data and made general recommendations for design.
Low GWP Refrigerants
In the same session, a presentation was given by researchers from Oak Ridge National Laboratory. Kashif Nawaz, Jeff Munk, Bo Shen, Ahmed Elatar and Walt Hunt delved into the consequences of using R1234yf refrigerant in a HPWH. They noted that future work would involve an optimized HPWH using a new evaporator with the system optimized for R-1234yf charge.
Copper Tubes in HPWHs
The session “Modeling and Optimizing Tanks, Heat Exchangers, and Controls” was of special interest to users of efficient small diameter copper tube MicroGroove technology. Yoram Shabtay from Heat Transfer Technologies and Kerry Song from International Copper Association reported on “Optimization of Copper-tube Coils for Energy Efficiency and Charge Reduction in Heat Pump Water Heaters.”
Tank type water heaters are the most common water heaters and are very promising for reducing peak demand because of their large energy storage capacity. Modeling of the tank, the heat exchanger, and controls were explored in the presentation by Shabtay and Song. The slideshow is posted online at
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Figure 1 — HPWH case studies were presented by Yoram Shabtay at the 2021 Hot Water Forum. HXSim 3D results show temperature distribtuions in an evaporator coil with 5 mm outer-diameter copper tubes.
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More Modeling from GTI and ORNL
In the same session, Divya Thiagarajan and Jonathan Harrison of Gamma Technologies Inc. (GTI) introduced a physical model of buoyancy and flow phenomena within the tank itself.
The third presentation from ORNL and the Department of Energy describes a method to minimize electricity cost during time-of-use electricity pricing. Authors Kadir Amasyali, Jeffrey Munk, Kuldeep Kurte, Teja Kuruganti, and Helia Zandi detailed how controls could be used to save 11 to 33 percent in electricity costs compared to the baseline.
Week Two Plenary: Compelling Statistics
The 2021 Hot Water Forum consisted of four sessions per day for four days spread over two weeks. The second week was kicked off by a plenary from the New Buildings Institute (NBI) and Advanced Hot Water Initiative (AHWI). This presentation featured excellent statistics making the case for HPWHs and fully capturing the magnitude of the mission and goals of NBI-AHWI.
Not Only Residential
The third session on day three (i.e., session “S11”) was on Next-Gen Commercial Water Heating Products. These are large WHs, including some with large evaporators split from the large hot water tank.
Ryan Hamilton of Nyle Water Heating Systems described diverse products as well as experiments with alternative and natural refrigerants in split systems, including split outdoor evaporators.
In the same session, Lynn Mueller, Matt Wardlow and Elisa Kimus from the SHARC Energy Systems demonstrated an interesting way to save energy by optimally arranging water tanks in a commercial setting. SHARC is an incubator company associated with the Electric Power Research Institute (EPRI).
Last but not least, Cain White described a 40 kW HPWH that uses carbon dioxide (R744) as a refrigerant in commercial applications. These modules can be stacked to provide hot water for large commercial applications. The helical gas cooler with copper tubes was especially noteworthy in the design. White is the director of Commercial Product Management at Mitsubishi Electric Trane HVAC US.
HPWH Product Roundup
Amruta Khanolkar from the New Buildings Institute kicked off the final day of the Hot Water Forum by comparing residential HPWHs from Bradford White, Rheem, AO Smith, GE, Nyle, and SanCO2; and also commercial (central) HPWHs from SanCO2, Nyle, Colmac, Mitsubishi, AERMEC, Mayekawa and an unnamed US manufacturer that will release a new product in 2022.
CO2 systems from Sanden, Mitsubishi, and Mayekawa were among the commercial systems described and compared by Khanolkar.
All told, the 2021 Hot Water Forum exceeded expectations. The importance of this forum is underscored by the fact that water heating ranks third in terms of energy usage for domestic applications, exceeded only by space heating and space cooling.
A Virtual Gathering at Purdue 202ONE
The organizers of the Purdue Conferences were forced to postpone the biannual conference that normally would have occurred in July 2020; although there were aspirations to meet live in 2021, a decision was made to go “virtual only” for the rescheduled event, which was dubbed “202One.”
Destination Gather Town
The chosen “virtual setting” (i.e., “Gather” or “Gather Town”) was well suited for Purdue 202One. Papers and presentations could be viewed in advance and participants used an avatar to virtually “walk the floor” of Gather Town, striking up live video chats with authors and other attendees. Upon entering a virtual conference room in Gather Town, one could readily view the featured slideshow and paper and spontaneously interact with the original investigators as well as the assembled group.
The range of topics was quite extensive. Of possible interest to heat-exchanger engineers and appliance designers are papers on the following topics.
· Tube and fin research
· Coil circuitry (including distributor design)
· Refrigerants
· Appliance design
There were several papers about the properties of tubes, including copper tubes, and in some cases specifically on MicroGroove smaller-diameter copper tube technology.
NOTE: Purdue 202One papers can be accessed online from this webpage. https://docs.lib.purdue.edu/iracc/ Simply type the paper number that is referenced here in the search box provided on the webpage.
A Prize Winning Technique
Min Che and Stefan Elbel from the University of Illinois Urbana presented on “Experimental Evaluation of Local Air-Side Heat Transfer Coefficient on Single Fins” (Paper 2176). The paper won first place for doctoral candidate Min Che in the student competition. https://mechse.illinois.edu/news/40254.
Che described new experimental methods for visualizing and quantifying Heat Transfer Coefficient (HTC) distributions on fin surfaces. The technique involves spraying a thin yellow coating (20 μm) on the fins and placing them in a wind tunnel. Tracer quantities of ammonia are present in the wind tunnel airflow, causing the color of the surface of the fins to change from yellow to blue. By correlating the rate of local color change with the rate of local mass transfer (and hence also heat transfer) local HTCs on the fin surfaces can be quantified.
First 3 mm Diameter Tube Heat Exchanger
The paper on “Design Optimization of 3 mm and 5 mm Copper Tube and Flat Fin Air-to-Water Heat Exchangers with Experimental Validation” (Paper 2185) is of particular interest to followers of MicroGroove Technology.
Authors included Daniel Bacellar, Dennis Nasuta, Song Li and Cara Martin from Optimized Thermal Systems, Inc. Beltsville, Maryland as well as Dale Powell of the Copper Development Association. The simulation results were validated by building prototype heat exchangers.
According to the authors, to the best of their knowledge, the experimental work is the first that performed experimental tests on a heat exchanger using 3 mm diameter copper tubes. The numerical optimization illustrated how, under equivalent geometry characteristics, a 3 mm diameter tube offers advantages with respect to thermal-hydraulic performance.ses like "for a limited time only" or "only 7 remaining!"
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5 mm tube diameter
and 19 fins per inch
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3 mm tube diameter
and 21 fins per inch
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3 mm tube diameter
and 28 fins per inch
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Figure 2 — Simulation results for MicroGroove copper tubes were verified by wind tunnel tests on actual heat exchangers. |
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Laboratory Validation of Fin-and-Tube Heat Exchanger Simulations
Researchers claim they can validate computer simulations to a high degree of accuracy, using a novel experimental apparatus that includes a small wind tunnel.
Results were presented in a paper titled “Development of Novel Experimental Infrastructure for Collection of High-Fidelity Experimental Data of Refrigerant to Air Heat Exchangers” (Paper 2222). The paper was authored by Saad Saleem, Craig R. Bradshaw and Christian K. Bach from Oklahoma State University; and Omer Sarfraz from Johnson Controls.
The data collection apparatus collects high fidelity experimental data for fin-and-tube heat exchangers for three operating modes: (1) single-phase refrigerant, (2) evaporator, and (3) condenser mode. The pumped refrigerant loop can control refrigerant test conditions as well as the flowrate to each individual heat exchanger circuit. The apparatus has been sized to test heat exchanger coils up to a capacity of 5 tons (17.5 kW).
The first test of the apparatus was carried out on a typical copper tube coil with aluminum fins. It is interesting that this four circuit coil can also be simulated with HXSim simulation software from the International Copper Association.
Novel Tube Shapes
A memorable technical article on novel tube shapes is titled “Experimental Study of a Novel Shape-Optimized Air-to-Refrigerant Heat Exchanger under Evaporator Conditions” (Paper 2539). The paper was authored by Ellery Klein, Vikrant Aute and others from University of Maryland and Yoram Shabtay from Heat Transfer Technologies.
Using the novel tube shape, a finless heat exchanger was designed with a 25 percent reduction in volume, 20 percent reduction in face area, and an 8 percent reduction of internal volume compared to a state-of-the-art, air-to-refrigerant heat exchanger; yet it was designed to have the same air-side pressure drop and a capacity equal to or greater than the conventional heat exchanger. The predicted and measured values show good agreement, with the performance verified under dry and wet evaporator conditions using R‑410A as the refrigerant.
Augmenting Nucleation on Copper Tubes
Numerous researchers have found that surface roughness can enhance pool boiling heat transfer. Most recently magnetic abrasive finishing (MAF) was used to augment the activated nucleation sites on the internal surfaces of copper tubes. The technique provided higher heat transfer coefficients for the in-tube flow boiling as expected.
“Heat Transfer and Pressure Drop Characteristics of Water Flow Boiling in Internally Enhanced Tubes” (Paper 2685) delivers the results from three laboratories. Three authors from Oak Ridge National Laboratory (Cheng-Min Yang, Kashif Nawaz, and Anthony Gehl) collaborated with two from the University of Florida, Gainesville (Hitomi Yamaguchi and Fang Xu) and one from Texas A&M University (Jorge Alvarado) to develop and test a copper tube internally enhanced using the MAF technique.
Balancing RTPF with MCHX
Moving beyond studies focused on tubes, several papers addressed tube circuitry and maldistribution.
As an indicator of the continued importance of such research, Khaled Ibrahim Alghamadi and Christian Konrad Bach from Oklahoma State University endeavored to balance a system that uses microchannel tubes in the condenser and 10 mm round tubes in the evaporator. Their results are given in a paper titled “Dynamic Modeling of Packaged Air Conditioner with Microchannel Heat Exchanger Condenser” (Paper 2267).
The reasons for using round tubes in the evaporator have to do with the maldistribution of refrigerant that can occur with microchannel heat exchangers. After reviewing the literature on modeling the system balancing, the authors point out that little work has been done on systems that include a combination of microchannel tubes and round tubes.
Optimizing the Distributors
Although the details of the research are beyond the scope of this overview, several papers on flow distribution are noteworthy.
Yufang Yao and Pega Hrnjak, from University of Illinois and Creative Thermal Solutions, respectively, presented a two-part paper on refrigerant distributors (Paper 2464). Part one (10 pages) is titled “Effect of flow regime before distributor on two-phase flow distribution” and part two (9 pages) is titled “Effect of orientation on performance of the refrigerant distributor.”
Their research demonstrates the effect of the flow regime at the distributor inlet on the uniformity of two-phase flow distribution. The flow regime is determined by mass flux, quality, and distance from the expansion device. A high-speed camera is used to visualize the two-phase flow regimes between the expansion valve and distributor; and also to interrogate the flow regime inside the distributor. A close study of both of these papers provides insights into the design of distributors and circuitry for evaporators.
Similarly, Saugata Sarkar, who is a senior thermal system engineer with Triumph Group Integrated Systems, provides insights into evaporator designs through modeling of ideal distributors in a paper titled “Computational Fluid Dynamics (CFD) Modeling of Two Phase Refrigerant Flow in Evaporator Distribution System” (Paper 2552).
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Figure 3 — The performances of these three ideal distributors were simulated by Saugata Sarkar, a senior thermal system engineer with the Triumph Group. (Illustration used with permission.)
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The more general topic of how to simulate distributors was tackled by Zhenning Li from ORNL and Vikrant Aute from University of Maryland. They outlined their algorithm for the optimization of circuitry in evaporators in a paper titled “Enhanced Integer Permutation based Genetic Algorithm for Optimization of Tube-Fin Heat Exchanger Circuitry with Splits and Merges” (Paper 2574). According to their case studies, optimal designs obtained using their algorithm exhibit higher capacity, lower pressure drop and better manufacturability compared to baseline designs.
Research on Refrigerants
Refrigerant blends are on the minds of heat exchanger designers everywhere as OEMs strive to reduce the GWP of refrigerants in AC, heat pump and refrigeration applications. The use of blends allows designers to make tradeoffs between GWP, flammability, cost and performance.
Ternary blends obtained mixing hydrofluorocarbons (HFC) and hydrofluoroolefins (HFO) have recently been proposed as substitutes for high global warming potential (GWP) fluids employed in refrigeration and air-conditioning. Several papers from the Purdue Conference give a preview of what is to come.
Ternary blends were also a hot topic on the program of the Thermophysical Properties and Transfer Processes of Refrigerants (TPTPR), an international conference that takes place every four years. This year TPTPR was a virtual event from September 1‑3, 2021. A paper on heat-exchanger simulations was presented at TPTPR 2021 by Yoram Shabtay, Kerry Song and Frank Gao of HTT and ICA. The TPTPR presentation and the paper titled “Simulation of the effects of copper tube diameter on refrigerant charge reduction in split AC systems and refrigerated cabinets” are available online at https://microgroove.net/hxsim.
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Figure 4 — Specialists in the Thermophysical and Thermodynamic Properties of Refrigerants were introduced to HXSim simulation case studies at the 2021 TPTPR Virtual Conference. For slideshow, technical paper and software download, visit www.microgroove.net/HXSim.
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Padovans Look at R455A and R452B
The University of Padova is renowned for its work on the thermophysical properties of refrigerants. Marco Azzolin, Arianna Berto, Stefano Bortolin and Davide del Col recently conducted research on two different zeotropic ternary mixtures: R455A, which is a mixture of R32, R1234yf and R744 (21.5/75.5/3.0% by mass composition); and R452B, which is mixture of R32, R1234yf and R125 (67.0/26.0/7.0% by mass composition).
They measured condensation and flow boiling heat transfer coefficients inside a minichannel (0.96 mm diameter) and inside a conventional tube (8.0 mm diameter) for these blends. The results of these methodical laboratory measurements were reported in a paper titled “Two-Phase Heat-Transfer of Low GWP Ternary Mixtures (Paper 210049).
ORNL Doubles Down on Refrigerant Blends
Researchers from Oak Ridge National Laboratories (ORNL) described a novel framework for optimizing low-GWP refrigerant mixture compositions. Using this framework, new refrigerants can be matched to the system. The condenser and evaporator circuitry configurations can be optimized simultaneously with the mixture compositions.
The case studies using an experimentally validated R410A Roof Top Unit (RTU) show that the proposed optimization approach can generate new binary and ternary mixtures and new circuitry designs to improve system EER, reduce refrigerant flammability, and maintain a low GWP.
This paper is titled “Optimization of Refrigerant Compositions for Low-GWP Refrigerant Mixtures Using Segment-by-segment Heat Exchanger and Detailed System Models” (Paper 2614). The ORNL authors are Zhenning Li, Bo Shen, and Kyle Gluesenkamp.
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Figure 4 — Shen and Li from ORNL described these three basic types of tube circuitry in a paper about low-GWP refrigerants.
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Emerson Weighs in on Low-GWP Options
The new refrigerant blends and the optimized heat exchangers must work in harmony with the compressors. Emerson weighed in on new refrigerant mixtures with a paper titled “HVAC Systems with Low Global Warming Potential Refrigerants: A Case Study” (Paper 2144) by Vijay Bahel, Rajan Rajendran, Brian Butler and Drew Welch, from Emerson, Dayton, Ohio.
The Emerson paper provides an excellent overview of things to come with respect to refrigerant blends. In the conclusion, the authors state key takeaways as follows: (1) we can conclude that R-32 and R-454B, two popular R-410A replacement candidates with a GWP below 750, both have system performance equal to or better than R-410A; (2) refrigerant options with a GWP below 300 all underperform versus R-410A. The authors also found electronically commutated motors (ECM) to be more efficient than permanently split capacitor (PSC) condenser fans and evaporator blower motors.
Effects of MicroFins on Blends
Ethan P. Matty and Brian M. Fronk from Oregon State University compared the condensation heat transfer and pressure drop for zeotropic refrigerant R454C and its individual components in a horizontal microfin tube with a 4 mm outer diameter. According to these authors, microfin tubes enhance heat transfer by several mechanisms: the microfins increase the internal surface area of the tube, the fins drain condensate from the fin tip to the trough region, and the microfins produce secondary flow structures.
Noting the limited data on HFO/HFC mixtures in microfin tubes, Matty and Fronk conducted experiments on the complete condensation of R454C, R1234yf and R32 for saturation temperatures of 40, 50 and 60 °C and mass fluxes from 100 to 600 kg/m2s. They compared their results on heat transfer and pressure drop to correlations from the literature; and they also calculated heat transfer enhancement factors and pressure drop penalty factors for each refrigerant. Their paper is titled “A Comparison of Condensation Heat Transfer and Pressure Drop for Zeotropic Mixture R454C and its Components, R32 and R1234yf, in a Horizontal Microfin Tube.” (Paper 210068)
The Multiple Benefits of Less Charge
No matter the HFC/HFO blend, lowering the refrigerant charge has the dual effect of reducing the system GWP and also the amount of flammable refrigerant in the system. Costantino Guzzari, Marco Azzolin, Sandro Lazzarato and Davide del Col from the Università degli Studi di Padova addressed this issue in the paper titled “Effect of the refrigerant charge on the system performance and mass distribution in air-to-water systems” (Paper 210064).
These authors analyzed the influence of refrigerant charge on the system performance and on the mass distribution in an air-to-water reversible heat pump working with R32. They used a mathematical model to predict the refrigerant charge within the heat exchangers. The results show that most of the charge is stored in the condenser and that an optimal charge can be found to maximize the system COP. The same model can be used to compare various refrigerants in terms of direct and indirect impact on the greenhouse effect.
Concepts in Appliance Design
Many of the results mentioned above directly apply to the development of optimized heat exchangers for improving the efficiency of appliances, including heat pumps for space heating and water heating; as well as air conditioners and refrigeration equipment. There were also papers specifically on heat pumps for clothes dryers and dishwashers.
Examples of papers on clothes dryers include a paper titled “Experimental Investigation of a Heat Pump Tumble Dryer with a Zeotropic Refrigerant Blend” (Paper 1012) from the Technische Universität Dresden; and a paper titled “Thermodynamic Analysis of Thermo-vacuum Clothes Drying Operation” (Paper 2406). The latter paper is a collaboration between Wilson Engineering Technologies, Inc., the Gas Technology Institute (GTI), and ORNL. It examines the intriguing concept of drying clothes in a vacuum in which case the speed of drying could be increased and the energy consumption decreased by the vacuum.
A dedicated heat pump for producing very high temperature water for a commercial dishwasher is described in a paper titled “Development of a High Temperature Water Heat Pump in Vent-Less Dishwasher Application” (Paper 2341) Daqing Li and Suresh Shivashankar, who are both from Emerson Commercial & Residential Solutions, in Sidney, Ohio, USA.
This brief synopsis paints a picture of ongoing research from national laboratories, universities, industry suppliers and OEMs. As fundamental research advances, it is clear that there is much room for improvements in the efficiency of heating and cooling appliances and equipment.
Scientific research on the refrigeration cycle, the thermophysical properties of refrigerants and the optimization of heat exchanger designs gives appliance designers new tools and technologies for efficient heating and cooling in residential, commercial and industrial applications.
Countdown to 2021 UN Climate Change Conference
As we look ahead to COP26, an important question looms: What can be done to further improve the energy efficiency of heating and cooling systems?
The 2021 UN Climate Change Conference (COP 26) is scheduled to take place in the city of Glasgow, Scotland from October 31 to November 12, 2021.
Although the conference was delayed by the global pandemic for one year, expectations are high as world leaders, policy makers and scientists gather for what promises to be a turning point in addressing climate change.
Aggressive-yet-realistic targets for the reduction of greenhouse gas (GHG) emissions will be deliberated in Glasgow. Progress has been made since the Paris Agreement was negotiated at COP 21 in 2015 but much more progress is needed to avert climate catastrophes in our lifetimes.
Energy production by solar and wind has increased significantly in the past 20 years. In many instances, it is now less costly to generate electricity from solar and wind rather than fossil fuels. The technology exists.
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Figure 6 — All eyes will be on Glasgow this Fall for the UNCCC (COP 26). |
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What is still lacking is the willingness to put the technology into action and scale up clean technologies by a few orders of magnitude if we are to be successful in scaling down reliance on fossil fuels.
Drawing down usage of fossil fuels such as coal, oil and gas is the key to reaching sustainability goals of the Paris Climate Treaty. Renewable energy resources such as wind and solar can replace coal-burning power plants.
Simultaneously, in transportation and buildings, the use of oil and gas can be drawn down through the electrification of automobiles and heating systems.
This transition is facilitated by developing and using high-efficiency systems that consume less energy.
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LORDAN RISES TO MEET CHALLENGES WITH HEAT-EXCHANGER EXPERTISE AND EXCELLENCE IN MANUFACTURING
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Collaboration with Customers Aided by HXSim Simulation Software
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Lordan is more than a heat exchanger manufacturer. Since it was founded in 1959, the company has partnered with dozens of OEMs. It remains competitive by continually pushing the “state of the art” in heat exchanger design. Collaborating with partners in commercial, industrial and residential applications, Lordan has consistently been an early adopter of the latest technologies.
MicroGroove technology has been no exception to this tradition. Lordan introduced Lord Seven (7 mm) and Lord Five (5 mm) tube technology into heat exchanger designs even before the International Copper Association launched its first campaign promoting MicroGroove smaller diameter copper tubes. Figure 1 illustrates the higher capacities realized using MicroGroove tubes.
While not limiting itself exclusively to copper tubes in its designs, the bulk of Lordan’s business revolves around copper round tubes with aluminum plate fins, i.e., RTPF heat exchangers. Since its beginning, it has pushed the technology forward with innovative designs and advanced manufacturing methods.
Recently the company expanded its global presence. It now operates large manufacturing plants in northern Israel and in Wales and has logistical warehouses and sales offices throughout Europe and the United States. Lordan (A.C.S.) has headquarters in Kfar Szold, Israel.
The refrigeration industry is notoriously segmented, which results in continual product innovation. Mid-sized coil makers working with MicroGroove smaller-diameter copper tube can be found throughout Europe [1]. Lordan was among the earliest adopters of 5 mm diameter copper tubes. The company boasts that compared to tubes with 3/8 inch diameters, its Lord 5 RTPF products offer five advantages: volume saving, reduced weight, reduced refrigerants, energy savings, and RoHS Compliance. RoHS stands for Restriction of Hazardous Substances. It originated in the European Union and restricted the use of specific hazardous materials found in electrical and electronic products.
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Figure 1 — Smaller diameter tubes allow for higher capacity while reducing the refrigerant charge, materials usage and overall size of the heat exchanger. (Image Courtesy of Lordan,)
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Versatility is the Key to Success
Heat exchanger manufacturing is an extremely competitive industry. Even large companies have a tough time! In Europe, there are many large companies involved in the manufacture or heat exchangers for commercial and industrial refrigeration as described in a previous issue of the MicroGroove Update [1].
According to Peter Mostovoy, the one word that best characterizes Lordan is “versatility.” That is what separates Lordan from some of the giants in the commercial refrigeration industry. “Lordan is unmatched in terms of the number of different designs of heat exchangers that it produces in any given year,” he says.
Lordan collaborates with partners across a wide range of industries and broad scope of applications. Heat exchangers have been designed by Lordan for network-server farms, industrial heating and cooling, semiconductor cleanrooms and medical equipment. These applications require precise temperature control and resistance to harsh environments as well as resilience and reliability.
Lordan thermal systems engineers have custom-designed heat exchangers for cooling the superconducting magnets that are used in particle accelerators as well as superconductor magnets used in magnetic resonance imaging (MRI) equipment.
“Our typical customer in the commercial and industrial sectors may ultimately only have a need for 500 to 1000 heat exchangers, depending on the application,” says Mostovoy. “Size may vary from a small condenser or evaporator for an R290 vending machine or refrigerated display case to an enormous twelve-meter heat exchanger for an industrial application. We use a variety of advanced manufacturing equipment, including tube benders and tube handlers as well as mechanical expanders and automated brazing using robotics. A special hydraulically driven bullet expander is used to expand tubes in some of our larger heat exchangers.”
Lordan keeps an inventory of many fin dies with predetermined tube spacing and fin types, including tubes of different sizes, as outlined in its main catalog [2]. Lordan can offer its customers fin dies with a variety of fin types (e.g., slit fins, louver fins, etc.) and tube diameters down to five millimeters. The quality control meets the highest industry standards. It also offers many types of anti-corrosive coatings.
Lordan collaborates with its customers on all aspects of the design, prototype construction, volume manufacturing, inspection and shipping logistics. Wherever possible, existing fin dies are used to minimize upfront costs, especially for small manufacturing volumes. The off-the-shelf fin designs are described in the Lordan catalogs.
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TABLE I. Various parameters can be easily adjusted varied through HXSim's rich database and graphical user interface. |
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Cold-Climate R290 Heat Pump: An HXSim Case Study
Recently, Lordan engineers began using the HXSim simulation software that is available free-of-charge from the International Copper Association.
As an illustration of the use of HXSim, Mostovoy shared a design for an outdoor evaporator for a cold-climate heat pump. The refrigerant picks up heat in the evaporator and this heat is transferred (via compressor and condensers) to a water tank that is also located outdoors. The hot water can be used directly or distributed indoors for space heating. In this manner, a single cold-climate evaporator can be used for both water heating and space heating with R290 as a refrigerant.
The present case study focuses on the design of the outdoor evaporator.
The evaporator block has a 1028.7 mm height and a 50.8 mm depth. The tube circuitry is such that there are two hairpin tubes (four tube lengths) in each circuit. These are staggered so that there are four tubes lengths per row across the airflow direction.
The evaporator is an L-type block, which means it has three sections: The first section has a length of 890 mm; the middle section encompasses a 90 degree bend with a radius of curvature of 100 mm; and the third section has a length of 300 mm.
All of this data is easily entered into the HXSim software block design and tubes are readily connected through an intuitive point-and-click graphical user interface.
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TABLE II. HXSim Simulation Results for an Outdoor Evaporator Design for a Cold Climate Heat Pump. (This heat exchanger design uses 5 mm diameter MicroGroove inner-grooved copper tubes and 150 grams of ecofriendly R290 natural refrigerant. |
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A single copper manifold serves as the inlet to the 54 tube circuits in evaporator. With each circuit containing four tubes, that brings the total number of tubes to 216 (that is, 54 x 8). Similarly a single copper manifold serves as the outlet for these same 54 circuits, delivering the refrigerant to the compressor.
Since the same pattern of two paths is repeated over and over again the “copy path” command in HXSim can be used to quickly construct the heat exchanger circuitry from the bottom to the top.
The user can select the type of fins and tubes. For illustrative purposes, 5 mm copper tubes are chosen with and without inner grooves. Once additional data is entered (e.g., air flow rate, mass flow rate according to Table I) the simulation can be run and the performance results can be calculated. A mass flow rate of 196 kg/h and airflow rate of 10441 m3/h were used for this particular simulation. This particular design calculates a capacity of 14 kW for grooved tubes.
According to Mostovoy this result is in excellent agreement with laboratory measurements on the manufactured heat exchangers within a few percent.
Figure 2 shows a close up of the evaporator design with just one path highlighted. The tube highlighted in red is connected to the outlet tube.
Figure 3 shows the 3D resuts of the temperature distribution. The HXSim program can also display 3D graphic results for refrigerant temperature, pressure, enthalpy and quality.
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Figure 2 — The 3D heat exchanger design can rotated, enlarged and translated on the display before printing. In this view, a typical circuit path has been highlighed to show how four tubes are connected as well as connections to the inlet and outlet tube. The connection ot the outlet tube is highlighted in red. This heat exchanger contains 54 such paths.
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Figure 3 — Results can be displayed as tables, plots or 3D graphical visualiztions. Graphical results are available for refrigerant temperature, refrigerant pressure, refrigerant enthalpy and refrigerant quality, i.e., ratio of gas to liquid. These same results can also be plotted along any refrigerant path.
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R744 Gas Coolers with Cu-Fe Copper Alloys
Hydrofluorocarbons, also known as HFCs or F-Gases, are potent greenhouse gases (GHGs). HFCs are notorious for leaking into the atmosphere while in service and when discarded. HFOs and HFO/HFC blends have been proposed as HFC replacements.
With its ultralow global warming potential (GWP) of one, CO2 is very attractive as a refrigerant. The technology for transcritical (TC) CO2 has steadily improved in the decades following the 1987 Montreal Protocol. Now CO2 refrigerant (also known as R744) is very competitive for supermarkets, warehouses and industrial cooling as well as heat pump water heaters, space heaters, clothes dryers and other applications.
Europe led the way in developing refrigeration systems that use R744 as an ecofriendly natural refrigerant. Lordan is one of many companies across Europe, the Middle East and South Asia meeting the robust demand for R744 heat exchangers made with smaller diameter copper tubes.
Gas coolers for the TC R744 refrigeration equipment must withstand extremely high pressures. Lordan is actively developing heat exchangers for R744 TC gas coolers using copper-alloy tubes with small percentages of iron. Finely dispersed iron precipitates in the alloy structure of these copper-alloy tubes significantly increase their yield strength.
Copper-iron alloys are described in DIN EN 12449 (Copper and copper alloys - Seamless, round tubes for general purposes, 2019). The copper-iron alloy UNS C19400, which also contains a small amount of iron, has a yield strength that is more than fifty percent higher than UNS C12200 copper.
As a first approximation for thin-walled tubes, the “hoop stress” equals the internal pressure times the radius of the tube divided by the tube wall thickness. In other words, the hoop stress decreases as the diameter of the tube is decreases for a given internal pressure.
Unless it has a very thick wall, a tube with a 3/8 inch (9.525 mm) diameter that carries a refrigerant at high pressure could burst due to the very high hoop stress.
Tube diameters of 5/16 inch (7.9375 mm) or 1/4 inch (6.25 mm) are commonly used for R744 applications. The hoop stress in the tube drops in the ratio of 6 to 5 to 4 as the diameter is reduced from 6/16 to 5/16 to 4/16 inches, respectively (that is, from 9.525 mm to 7.9375 mm to 6.350 mm). Some coil manufacturers are using copper tube diameters of only 5 mm since such smaller diameter tubes can withstand high internal pressures with thinner walls.
One way to increase the pressure rating is to increase the tube wall thickness. Doubling the tube-wall thickness roughly halves the stress in the wall of a tube for a given internal pressure. Conversely, either of the first two approaches, i.e., using a smaller diameter tube or a high strength copper alloy, allows one to use thinner tube wall thicknesses. Thin walled tubes decrease the cost and the weight of heat exchangers.
Lordan makes R744 gas coolers with 5 mm tube diameters. By using a Cu-Fe alloy, Lordan can reduce tube wall thickness from 0.7 mm to 0.4 mm.
Tubes made from a high strength copper-iron alloy can withstand higher pressures. Coil makers such as Lordan successfully use this approach to increase the pressure rating of the coil itself.
High strength copper alloys are also used for the refrigerant lines that run to-and-from the gas cooler. (For more on this topic, see the slideshow presentation by Yoram Shabtay [3].
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Collaboration with HXSim
The simulation capabilities of ICA’s HXSim closely parallel the production capabilities of Lordan. In other words, heat exchangers simulated on HXSim typically can be built by Lordan. This capability reflects the versatility of Lordan.
Lordan engineers have found HXSim to be a useful simulation tool that is also easy to use and share with its customers. “HXSim facilitates technical communications with our customers. If a customer comes to us with a design that can be simulated on HXSim then our engineers can quickly understand what is needed and wanted. The user-friendly interface captures the inputs in tabular form. Our engineers can then come back to customers with proposals and recommendations for improvements. The customers can see the advantage by running the simulation themselves.
“if you can simulate a heat exchanger on HXSim then there is a good chance that Lordan is capable of manufacturing a prototype. Practically any heat exchanger that can be designed with HXSim can be built by Lordan,” says Mostovoy. “HXSim empowers OEMs at the early stages of heat exchanger design. Our engineers have deep experience in the design of heat exchangers that goes beyond the HXSim but the HXSim is a good starting point.”
The software is available at no charge to qualified designers.
“Simulations of performance using ICA’s HXSim software are very good,” says Mostovoy. “We have used various other software programs, including our own internally developed programs. HXSim makes it very easy to enter the physical geometry, including tube spacing and fin types, and choose the refrigerant, flow rates and temperatures.
“The performance predictions are quite accurate compared to our laboratory measurements and simulations using other software,” he adds. “The HXSim software is very satisfying and easy to use. We are recommended it to our customers and partners. It's a good learning tool that allows for different tube circuitries, tube diameters, fin types and refrigerants to be rapidly evaluated and key decisions to be made without building prototypes. It is a useful tool that is easy to use.”
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Conclusion
Lordan continues to uphold its reputation for versatility and cutting-edge technology. “As AC, refrigeration and heat pump OEMs face the challenges of producing efficient, low-GWP products to meet the global demand for climate friendly products, Lordan stands ready to design, build and deliver the best heat exchangers for any given application. It’s what we do!” concludes Mostovoy.
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"In the Spotlight" References
1. MicroGroove Coils Span the Globe: Europe is Eco-Friendly, MicrogGroove Update, Volume 10, Number 2.
2. "Weathering Extreme Conditions," Lordan Catalog, page 11.
3. Yoram Shabtay, “Advantages of Small Diameter Tubes in Transcritical Refrigeration Cycles,” ATMOsphere America Conference, Atlanta, Georgia, June 2019.
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White Papers Recently Published in Appliance & HVAC Report
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Yoram Shabtay and Kerry Song, “Smaller-Diameter Copper Tubes Support Three Trends in Ecofriendly Appliance Design,” Appliance & HVAC Report, Vol.3, No. 1 (January 2021) pp. 43-51.
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Yoram Shabtay and Kerry Song, “Heat-Exchanger Simulations Fast-Track Adoption of MicroGroove Copper Tubes,” Appliance & HVAC Report, Vol. 2, No. 4 (September / October 2020) pp. 14-21.
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2020 ATMOsphere America Virtual Conference (slideshow)
Yoram Shabtay, “Heat Exchanger Simulation Tools Help to Optimize the Use of Natural Refrigerants with MicroGroove Smaller-Diameter Copper Tubes,” 2020 ATMOsphere America Virtual Conference.
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