Mother Nature doesn’t have any diplomas hanging on the wall, but has often proved to be a pretty good design engineer nonetheless. As more researchers come to realize that, many are finding ways to successfully adapt nature’s solutions to real-world design problems, and the efforts are having a significant impact on products as diverse as medicines, floor coverings, and refrigerators.

Some of those adaptations have now been employed in the realm of air moving applications. As researchers observe the ebbs and flows of fluids found in nature, they have absorbed lessons that have led them to create innovative fan designs. By adapting the concepts that underlie how fluids flow in nature, PAX Scientific of San Rafael, Calif., has developed fans that can reduce power consumption, reduce noise, increase airflow output, or combinations thereof.

The company specializes in “biomimicry,” a term coined by Janine Benyus, author of “Biomimicry: Innovation Inspired by Nature” and a member of the board of directors of the PAX Group. The term derives from bios, meaning life, and mimesis, meaning to imitate. In a nutshell, borrowing a design idea from nature and replicating it to fit into a man-made application.

Enlarge this picture Fig. 1. In comparing a 95-mm evaporator fan for a refrigeration application, the PAX design required 25 percent less power for equivalent airflow and dropped sound by half.

The company was founded in 1997 by Jay Harman. As a naturalist with the Australian Department of Fisheries and Wildlife (DFW), Harman logged thousands of hours studying the flow patterns of ocean and air currents. He also observed other examples of fluid movement such as tornadoes, fire storms and water spouts, as well as much more common phenomena such as water draining out of the bathtub, says Kim Shekar, vice president of product development for PaxFan.

Harman worked for many years to isolate the geometries that underlie natural fluid flows. His observations led to design principles that were contrary to generally accepted practice. Historically, devices employed to move liquids and gases — from paddleboats to propellers, fans and pumps — have been designed under the assumption that a straight line is the path of least resistance. Harman’s observation differed from this assumption. Fluids, he discovered, always want to follow a particular path, not a straight line.

From these examples, Harman began seeing recurrent patterns in nature, specifically spiraling, logarithmic shapes, that is, shapes whose curves are mathematically defined by logarithms. Seaweed, for instance, would spiral as a wave crashed over it and remain unscathed. By “going with the flow,” the underwater plant remained undamaged. In the shell of a mollusk he saw the same three-dimensional logarithmic spiral that he saw in the twisting, turning kelp and noticed that the fluids would flow centripetally -— toward the center — with less friction and more efficiency.

Made of steel or aluminum, the Delphi axial Fan is available in sizes from 17 in. to 30 in. and is suitedfor applications such as condensing units and heat pumps.

At PAX Scientific, researchers use Computational Fluid Dynamics (CFD) and CAD software to design the fans. With the CFD software, numerical methods and algorithms are used to solve and analyze problems that involve fluid flows. This technology is based on the Navier-Stokes equations, which establish that changes in momentum in infinitesimal volumes of fluid are the result of viscosity, changes in pressure, gravity, and other forces acting inside the fluid.

The result of these efforts is a blade design whose curves and angles reduce turbulence before, during, and after air makes contact with the fan blade. Sometimes the number of fan blades change — one OEM went from using a fan with six blades to a fan that uses three blades. Often, the blades run at higher RPMs, but consume less energy.

The geometry of the curved blades is such that the blades generate a vortex on their downstream sides. The fans “entrain” the air coming into the fan and accelerate air toward the center, creating a directed vortical flow that decreases turbulence. Traditional thinking in fan design was that producing laminar, straight-line flow was the best way to achieve smooth, non-turbulent flow. The PAX approach significantly departs from that conventional thinking by recognizing that vortical flow is the optimal path to achieving smooth, non-turbulent flow. In the same way a spiraling football or spinning bullet delivers a stronger and more stable trajectory, a vortical air-flow delivers a stronger and more stable stream of air. By taking this new approach, PAX engineers have been able to reduce energy requirements in fans and other rotors from between 10 and 85 percent, depending upon the application. The new blade design method also reduces noise levels from 30 percent to 75 percent, depending on the application.

Enlarge this picture Fig. 2. In developing solutions to improve efficiency of a condenser fan, PAX came up with two solutions. One required less power for equal airflow, while the other increased airflow for the same power as the existing baseline fan required.

The actual shape and pitch of the blade, as well as the number of blades used, all depend on the particular application and is an area the company declines to discuss in detail. The fan blades are often matched to the motor output and the packaging that surround it. “In many situations, we seek to design a PAX solution that is fairly similar to the current existing solution, so that it is easier to integrate into the application,” says Shekar.

And, these applications seem to be growing, as technology based on PAX’s streamline principle begins to enter the marketplace. To commercialize its technology, PAX Scientific granted master licenses to its spin-off companies, PaxFan, PaxIT, and PaxAuto. PaxFan holds the license for fans in the appliance, HVAC/R and industrial process segments. PaxIT is licensed for computer cooling applications. PaxAuto’s license covers engine and compartment cooling for automotive applications. These companies’s then license the technology to other companies and work with them to design products. Two such licensees are A.O. Smith Electrical Products, Tipp City, Ohio, and Delphi Corp., Troy, Mich.

Testing at PAX, as well as Delphi and A.O. Smith, appears to bear out the claim of improved performance when using fans designed using PAX’s techniques. The tests examine different goals, whether it is to improve airflow output with the same size motor or get the same output with a smaller motor. In other applications, the goal is to reduce noise, and in some applications they are looking to achieve a combination of desired benefits. Sometimes, trade offs need to be made.

A fan based on PAX technology that was used in a refrigeration evaporator application. Photo: PAX Scientific.

At PAX, researchers have studied a number of cooling applications. In one example, a motor manufacturer asked PAX to develop new refrigerator evaporator fans to improve energy efficiency. The effort was part of the manufacturer’s actions to achieve Energy Star certification for the appliance.

The application used a 95-mm fan operating in 0.03 in. H20. (See Fig. 1). The benchmark fan produced 58 cfm, while the PAX fan produced a comparable 57 cfm. At the same time, the PAX fan reduced power consumption some 25 percent, 5.55 W to 4.15 W, and reduced noise by half from 0.6 sone to 0.29 sone. (A sone is the perceived unit of loudness. One sone is roughly comparable to the sound a quiet refrigerator makes in a quiet room.)

Another test looked at reducing noise and power usage in an air conditioner condenser fan. In this case, PAX developed two solutions to replace an existing 560-mm fan. (See Fig. 2). The first allowed for reduced torque to run the fan while achieving the same output. It achieved a 25 percent reduction in power in the air conditioning unit and a 3dba drop in fan and motor sound level. The first test consumed 92.0 W power, dropping from 121.9 W, and reduced noise from 57.4 db to 54.2 db.

Enlarge this picture Fig. 3. A.O. Smith’s testing of a PAX fan showed that airflow can remain about the same, while greatly reducing power consumption.

The second solution increased output 12 percent and decreased the fan motor noise by 4dba. Keeping the power requirement the same, 121.9 W, it generated more CFM, increasing from 206.8 to 243.2 cfm. Thus, the manufacturer was provided with two different options, one which would allow the product to feature more airflow, but consume the same amount of power, and the other a product that delivers less airflow, but consumes considerably less energy.

Range hoods were also tested. In one case, the blade geometries reduced required shaft torque by 52 percent, which would have allowed the manufacturer to use a less expensive motor. For unrelated reasons, the project was not pursued, but if implemented, the manufacturer could have replaced a 4-pole barrel motor with a 2-pole C-frame motor and saved $3.50 per motor.

For HVAC/R applications, A.O. Smith has done extensive studies of PAX fan designs and how best to integrate the technology with its motors. They are marketing their prototype fans to customers interested in the technology for residential applications, particularly evaporator fans and condensers on the refrigeration side.

An image of a PAX-designed fan showing the hub.

Studies by John Belko, senior product design engineer for A.O. Smith, whose findings were reported in “International Appliance Manufacturing 2008” (p. 30), found substantial energy and noise savings at similar outputs in both bench and in-unit testing of a refrigeration evaporator fan.

Traditionally, an evaporator fan uses an ordinary axial fan, which tends to throw the air outward and often requires a shroud to redirect airflow. Belko found that with the PAX fan — and its centripetal capabilities — the airflow was better directed and eliminated much of the turbulence that could cause drag and vibration and ultimately reduce efficiency and create noise.

In addition, Belko found he needed less input power to achieve the same output capacity. Bench testing of a 100-mm fan in a wind tunnel at 0.02 in. – 0.03 in. H2O of static pressure, Belko found similar airflow levels were achieved compared to the baseline fan and there was a reduction in the energy required to power the motor and fan. (See Fig. 3). The tests showed that airflow was 57 cfm for the baseline, while the PAX unit was 55.8 cfm. Power use dropped from 5.56 W to 4.29 W, and noise was reduced in terms of sound power (41.4 dba to 39.5 dba) and sones (0.43 to 0.33 sone). (See Fig. 4.)

Enlarge this picture Fig. 4. In addition to improving power consumption and airflow, A.O. Smith’s tests showed a reduction in sound levels emanating from a PAX fan.

Belko also conducted a 3-day, in-unit test, which showed daily energy consumption dropping from 1.028 to 0.988 kWh per day. The in-unit testing of a 110-mm fan also found reductions in power requirements with similar outputs.

Delphi’s studies found similar benefits. The company has developed products for both the HVAC/R and consumer electronics industries and debuted them at the 2007 AHR Expo and the 2008 Consumer Electronics Show, respectively. Delphi designed direct current (DC) axial fans for the consumer electronics industry and metal axial fans for the residential and light commercial HVAC/R market. In addition, the company says it can custom design a fan to fit a particular application.

While energy and noise savings, as well as improved airflow output, depends on the specific application, Delphi’s studies of fans used in data server applications achieved a 15 to 20 percent reduction in power consumption and a reduction in noise of 2 decibels or greater, says Mark Parisi, product line manager, Air Management Systems - Delphi Thermal Systems.

Other studies performed both by Delphi and some HVAC OEMs found that the blade technology increased efficiency by 30 percent to 35 percent as compared to other fans in the marketplace, and increased airflow volume by 12 to 15 percent without having to increase power to the fan motor.

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These and other results look promising to all of the principals involved, and they feel that this is just the beginning. New products including centrifugal blowers are currently being researched. Other new applications may occur anywhere air needs to be moved or something needs to be fan-cooled, all of which can benefit from fan designs that improve air flow. Nature may have had 3.8 billion years to design its processes, but man-made designers are starting to catch up.

For more information, email: shekar@paxitllc.com