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issue: October 2002 APPLIANCE Magazine

Motors and Air-Moving Devices
Meeting Furnace Design Demands


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by Lisa Bonnema, Editor

Reducing Noise

After approximately 1 year of close collaboration between engineers from both companies, Jakel, Inc. not only developed a C-frame-powered 90+ draft inducer that exceeded ICP's noise level requirements, but the supplier also fulfilled other ICP requests, including cost reduction, an improved water management system, and extensive on-site testing.

To meet the low noise levels required by ICP, engineers had to reduce the vibration levels of the draft inducer. "Any time you have a rotating assembly, you can get vibration that is caused by the rotating part not being properly statically or dynamically balanced," explains Mike Eberlein, furnace product manager at ICP. "Jakel spent a lot of attention on the static and dynamic balance of the assembly."

According to Stu Gatley, director of Engineering at Jakel, the reduced vibration level was accomplished by redesigning the parts in the die. "It all comes down to the materials chosen and the design of the part," explains Mr. Gatley. "There was Finite Element Analysis (FEA) run on the blower wheel. We kept the vibration modes, the first natural frequency modes of the wheel, outside of the limits of an a.c. 2-pole synchronous motor. So we never run into the first natural frequency mode, and that helps us to maintain a vibration level that is about 60 percent of the competition," he adds.

"They were able to reduce the maximum vibration level by 40 percent over our previous supplier," confirms Mr. Eberlein of ICP. "Noise and vibration reduction is something significant that consumers - the ultimate end user - will appreciate. Homeowners don't like noise. They like quiet appliances."

Another critical design element was the materials for the inducer assembly. Jakel advised ICP to use RTP 199 from Winona, MN, U.S.-based RTP Company. According to Mr. Gatley, the compound, which uses polyproplyene as the base resin, was chosen because of its high-temperature rating and flexibility. "Usually when you require a high temperature rating, you add glass to a part, which makes it inflexible and brittle. You have vibration issues when you do that," he explains. "So we were looking for a part that had a high heat deflection temperature range as well as added flexibility to the part."

The material also made it easy for the draft inducer to pass ICP's standard Dead Blower Test. "What happens is the larger blower shuts off, so that the environment becomes very hot," says Mr. Gatley. "Our blower survives that condition, whereas our competition does not."

The Motor Is The Key

While every part of the inducer assembly - the blower, blower wheel, and motor - were crucial in achieving the performance results ICP was looking for, the motor was responsible for achieving the cost savings. "The C-frame motor is used because it is a more cost-effective motor to make than a 3.3-in motor," says Mr. Gatley. "The C-frame motor driving this is the first C-frame motor used in the industry on a 90-percent blower. It hasn't been done before."

According to Mr. Gatley, in the past, blower engineers weren't able to get the horsepower they needed out of a C-frame motor. "The reason we are able to match performance is because we are able to give a blower with the same blower air horsepower output with about 60-percent of the motor brake horsepower. In other words, we have increased the efficiency of the entire blower design to be able to cost reduce it," he explains. "There are some patented features inside the blower - some are pending still, some are patented. But basically we were able to increase the inside diameter of the housing to maximize it and allow the blower to work more efficiently." Mr. Gatley adds that other draft inducer manufacturers are now also starting to use C-frame motors in their blowers.

In addition to reducing cost and noise levels, Jakel also worked with ICP engineers to develop a rubber coupling with drain ports that helped improve the condensing furnace's water management system. "Our engineers and ICP engineers worked closely to figure out the optimum design and location of that part," explains Mr. Gatley. "If you get a gush of rain, the furnace has to be able to handle that so that it doesn't drown the blower."

According to Mr. Eberlein of ICP, the main reason it chose Jakel to develop its 90-percent draft inducer was because the supplier was willing to assist in the necessary testing. "Typically when you apply an inducer assembly to a gas furnace, there's a lot [of testing] involved, and Jakel was able to supply the manpower to do this," Mr. Eberlein explains. Jakel provided ICP with an on-site technician for 6 months.

While such services can be an added expense to the supplier, Jakel feels it is worth it, as more and more appliance OEMs are asking their suppliers to do more testing.

The new C-frame 90+ draft inducer products are now used on all of ICP's 90-percent condensing furnaces, including its Tempstar®, Comfortmaker®, Heil®, and Arcoaire®‚ brand furnaces. And this joint relationship will only continue; the companies have announced an exclusive purchasing arrangement in which Jakel will provide ICP with next-generation induced draft products.

 

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