Government regulations and educated consumers are forcing appliance manufacturers, HVAC/R companies, and makers of electronics to develop more efficient products that make less noise, and are more environmentally friendly. Because fans and their motors are often a root cause of power consumption and acoustic noise, these manufacturers are looking to their fan/blower and motor suppliers for answers.

The model R3G630 from ebm-papst is a backward curved motorized impeller.

To support their customers, fan manufacturers are incorporating new ways to design and manufacture these essential products, including the use of high-powered flow-simulation software. But researchers aren’t just looking to theory for ideas, they are also studying examples of efficient aerodynamics found in the world’s largest laboratory — nature.

In addition to re-examining fans themselves, companies are improving the systems that power and control them, which includes adopting new control technologies using electronically commutated (EC) motors and digital-signal-processing systems. Together, the technology gains in fan blades, motors, and controls are helping to achieve optimum efficiency and to help find the “sweet spot,” where air flow and velocity, heat transfer and back pressure, motor speed and load requirements, and other parameters come together to attain the most efficient operation possible.

An evaporator fan used in residential refrigeration applications.

Bill John, vice president of development & technology for ebm-papst Inc., Farmington, Conn., says that, in recent years, more companies are using computation fluid dynamics (CFD) technology to simulate the interaction of air flowing over and through turning fan blades. He says that, in the past, such techniques were generally only employed by the aerospace industry and other such manufacturers that had access to the high-powered computers needed to process sophisticated algorithms and perform the millions of calculations required to simulate airflow. But as processor power has increased in smaller computers, and costs have come down, fan and blower manufacturers are now in a position to use simulation methods once off limits.

John Belko, senior product design engineer for A.O. Smith Electrical Products, Tipp City, Ohio, was part of a project that coupled a nature-based fan blade design with the company’s DC brushless motors. He says that using CFD methods allow product designers to better visualize airflow and create a product that promotes smooth airflow over the form of the blade, rather than having the air being ripped apart, creating eddies and reverse flow through the blade passages. “The more streamlined the design, and the more that you can get the air to follow the shape of the blade, the less turbulence there is, and that is usually a pretty good measure of efficiency,” says Belko.

New axial fans from ebm-papst range in size up to 800 mm diameter. Backward curved impellers are available up to 630-mm diameter.

John says that ebm-papst’s impellers have been studied with CFD, but the concentration has been on axial-fan impellers as well as backward-curved centrifugal impellers. This technique has helped to design the sweep angle and blade width of some of the company’s EC 5-bladed fans. 

Nature’s way

In addition to using computer simulation, some suppliers are beginning to look to nature to better design their fan blades. At least two companies, A.O. Smith and Ziehl-Abegg, have developed new fan technologies based on “bionic” or “biomimicry” techniques.

Ziehl has one product on the market, the FE 2 Owlet axial fan, and another product in development, the CPro. Duncan Russell, executive vice president of Ziehl-Abegg USA, Greensboro, N.C., says his company is committed to combining physics with bionics to improve the design of its products.

Using an owl as a template — because it is the quietest predator in the sky — the company tweaked its blade geometry, added winglets to the blade tip, and created a serrated trailing edge. The new blade design helped the company achieve significant reductions in noise levels, Russell says. Comparing the Owlet to a prior product, he says that testing showed noise levels had been reduced by 6 db. “The human ear can detect about a 1 db to 1.5 db difference,” he says. “We went into the project with the hope of reaching a 3 db improvement. Hitting 6 db was more than we could have expected.”

The Owlet fan from Ziehl-Abegg. Researchers studied an owl to develop the fan blade design.

Another example of borrowing from nature is Ziehl’s Cpro, an impeller designed for use on centrifugal fans. The Cpro is modeled partly on the shape of a water droplet, as well as insights gained from the aerospace sector. Computer modeling helped the company tweak the blade including rounding off the blade’s leading edge. The Cpro impeller is available in diameters ranging from 250 mm to 630 mm to supply airflow volumes of up to roughly 28,000 CMH at pressures of up to 2,500 Pa.

Teamwork

Enlarge this picture Fig. 1. C-frame dyno curve with load line.

The desire for noise reduction and better efficiency are two of the reasons that A.O. Smith teamed up with PAX Scientific, San Rafael, Calif. PAX Scientific is an engineering research and development firm that has expertise in the flow of fluids, and it has adopted these concepts to the flow of air and gas. The company licensed its fan blade design to A.O. Smith for evaporation blowers that will be used in residential refrigeration and kitchen and bath fans (110 mm).

Enlarge this picture Fig. 2. C-frame efficiency curve.

In in-house testing of an evaporator fan prototype, the company found that the PAX fan consumed about 26 percent less energy as compared to an axial fan and was 50 percent quieter.

The fan was developed over several iterations as both companies learned more about each other’s technology. In some cases, the fan would load the motor too much, and PAX would need to look at maintaining the fan’s performance while reducing the load. On the flip side, A.O. Smith would look  at the fan design and decide to try and better develop a more robust motor to boost the operating point RPM.

Enlarge this picture Fig. 3. Wind tunnel performance comparison.

Mark Olson, a marketing manager for A.O. Smith Electrical Products, who was involved in the product’s development, says that the most efficient fan blade in the world will not solve all problems if it runs at an inefficient point on a motor-speed-torque curve. (See Fig. 1.) “We worked together on the design and to maximize motor efficiency and hit the sweet spot on the speed torque curve and the operating curve of the fan blade,” he says. (See Fig. 2.)

Just as the two companies developed multiple versions of the product to find the optimal configuration, the same can be said of specific applications. A.O. Smith and other companies will use modeling techniques to develop application-specific systems based on the application’s specifications.

Varying flow

An owl was used as the template for a fan blade design.

Applications may require that motor speed be modulated to match the appropriate load. Historically, says ebm-papst’s John, fan performance was controlled by deactivating one or more fans. That would drop the noise level, but would negatively affect output. If all of the fans can be left running and only the speeds altered, there is a much greater opportunity for noise reduction and efficiency.

For example, if only half the air was needed over a fan coil condenser, one way to meet the load would be to turn off half of the fans. According to John, by doing it that way, noise levels are reduced by about 3 db. If, however, all the fans are left running but turned down to half speed, the same amount of air is generated, but noise was reduced by as much as 15 db.

The Cpro from Ziehl-Abegg is patterned on a water drop.

An electronically commutated (EC) motor is one technology that facilitates this, John says. The company offers a range of brushless motors in both AC and DC versions, in a variety of sizes, that offer this capability. “This eliminates the need for variable-frequency drives and other devices that might be used, which also tend to be expensive and not as efficient as EC motors,” he says.

Ganging together multiple fans can also increase efficiency. For instance, Soler & Palau North America, OEM Products Division of Montville, N.J., offers backward curved motorized impellers that can be grouped for greater efficiency. A backward curved impeller is a centrifugal air-moving wheel with blades inclined in the direction opposite to the direction of rotation. The backward curved motorized impellers employ an external rotor motor. The fan blade assembly is press fit onto the external rotor which spins on the outside of the stator. The fins are curved against the direction of flow, which pushes the air, says Carl Giordano, Senior Vice President & General Manager.

An air flow testing lab operated by Soler-Palau.

While the impellers only produce, at maximum, about 2 in. of static pressure, they can grouped together to increase total airflow. In a typical configuration, the fans are installed in a tray and situated along the same plane, and they pull the air in the same direction and exhaust it in the same direction. “So,” says Giordano. “If you want to filter or cool air, the fans would be placed behind the filter or behind the heat exchanger and the impellers will pull air through that medium and then into the impeller throat and exhaust it in the back of the unit.”

The impeller does not require a housing to work, which gives the designer an “elegant solution” to a number of different applications. The impellers feature permanently sealed ball bearings and can operate in any orientation. “They can be mounted upside down, sideways on a vertical plane or on a horizontal plane,” says Giordano.

Soler-Palau’s sound testing lab.

The permanent-split-capacitor motors come in about a dozen sizes ranging from 5 in. to about 14 in., 115 V and 230 V, and are single phase, speed controllable. “That has the benefit of allowing the designers to change the RPM, which directly changes the air flow and static pressure to meet the requirements of each particular application,” he says.

For more information: A.O. Smith email: John.Belko@aosepc.com
ebm pabst email: Jamie.Perkins@us.ebmpapst.com
Soler & Palau, North America email: cgiordano@soler-palauinc.com
Ziehl-Abegg USA email: duncan.russell@ziehl-abegg.us

Sidebar: Eficient Mixing

Ametek Nautilair blower

Another application for a blower is in gas combustion appliances, where the blower is used to provide an efficient solution for mixing air and gas before combustion, resulting in high efficiency and low emissions.

The premix gas blowers deliver a measured air-fuel mixture to the burner with turndown ratios up to 10:1. The gas is injected either at the fan inlet or outlet to ensure optimum combustion efficiency resulting in lower NOx and CO emissions, according to a white paper from ebm-papst Inc., Farmington, Conn.

Ebm-papst offers premix gas blowers that are sized for small gas appliances and furnaces up to multi-million BTU gas burners, says Bill John, vice president of development and technology for ebm-papst. The blowers feature brushless DC-motors with integrated electronics and the blower speed can be adjusted over a wide range using a PWM (pulse width modulation) signal.

Kent, Ohio-based Ametek targets the high end residential and commercial hot water and boiler markets, or any products that are greater than 125,000 BTU”s.

All Ametek Windjammer blowers utilize brushless DC motor technology that runs at a maximum speed between 12,000 and 14,000 rpm.  Models operate at 120 or 240 VAC line input, which is then internally converted to a DC power to electronically commutate the fan to a given speed. The company has blowers that run up to 3 million BTUs.

The products, which evolved from the company’s Windjammer product line, which itself evolved from its vacuum cleaner products from Lamb Electric, feature a digital signal processor control, which allows the blower to vary the air flow to help achieve up to a 20 percent greater efficiency of the combustion and up to 20 percent lower NOx emission than conventional units, says Jodie McLay, east coast sales manager for Ametek.

Ametek is focusing on the premixed hot water and boiler applications, specifically the larger wall hung or floor mounted European style units, because they feel it has great growth potential in North America. He says it is an environmentally friendly product that is used extensively in Europe, but makes up only a few percent of heating systems in North America. “In the U.S., the majority of the homes use forced hot air instead of base board or radiant heat, but eventually we will see radiant heat used more and more,” says McLay. “With these hydronic systems, they allow efficiencies to increase from 82 to 96 percent, which could result in energy cost savings for 20 to 25 percent each month in large applications.”

For more information:
Ametek email: Jodie.McLay@ametek.com
ebm-papst email: Jamie.Perkins@us.ebmpapst.com