When is it appropriate to replace the existing motor with a higher efficiency motor? How can the proper information be communicated to customers so that they make the correct decision?

A direct-drive furnace motor. (Photo courtesy of Emerson Motors.)

Residential Motors

The News: How can motor efficiency affect the overall efficiency of a residential forced-air heating-cooling system?

Mallon: A higher efficiency motor operates at lower temperatures. It generates less heat. Therefore there is less heat which must be removed during the cooling cycle.

For example, if a 3/4-hp furnace blower is 60 percent efficient, it generates 373 watts of heat. If that same motor were 70 percent efficient, it would only generate 240 watts of heat. Your air conditioner would have to get rid of 133 more watts of heat in the 60 percent case. As you can imagine, 133 watts is roughly equivalent to turning off one more 150-watt light bulb. So we are not talking about much.

Drexler: Certainly, the energy used in a heating-air conditioning system is mainly converted to heated or cooled air. Despite this fact, even small boosts in efficiency can noticeably lower the total operating costs of the system.

The News: Does it make sense to replace an older motor in an older HVAC system with one of the newer motors? What kinds of considerations are there for this type of replacement?

Drexler: I would say that the major gains to be had would be in improved heat transfer devices and more efficient compressors, as opposed to more efficient motors.

Mallon: [It makes sense] in some cases. If your older system uses a shaded-pole motor, definitely yes. Shaded-pole motors are only 33 percent efficient. However, not many were ever used in furnaces with air conditioners.

Also, [it makes sense] if the motor is being used 100 percent of the time to facilitate the use of an electronic air filter. Some of the newer technology motors, which use electronics, can give the user significant savings.

The typical furnace motor is an induction motor. These motors have a peak efficiency at only one speed. This speed is usually only 10 percent less than the synchronous speed. For example, if the motor is a six-pole motor, its peak efficiency of 65 percent would occur at 1,100 rpm. When the motor is on “circulate,” the motor operates as low as 600 rpm. It is doing a lot less work, but its efficiency has fallen from 65 percent to 20 percent.

If we could avoid this loss of efficiency, we could save many watts, especially if the motor is operated 100 percent of the time. The only way to do this is either to go to a brushless permanent magnet motor, switched reluctance motor, or use an induction motor with a variable-frequency drive. Any of these would prevent any efficiency fall-off at the lower speed.

The News: How old is too old for just a motor replacement? In other words, where would a contractor draw the line and recommend that the customer purchase a whole new furnace?

Mallon: If the furnace is not an 80 percent or above efficiency furnace, serious consideration should be given to replacing the furnace.

Drexler: I’m not sure a line can really be drawn. Each instance is unique, and the homeowner would need to review the simple motor replacement cost versus a new unit and determine what his or her decision point would be.

Rescue multi-horsepower replacement motor for HVAC from Emerson.

Commercial Guidance

It benefits both contractors and owners if these replacements are planned, rather than performed on an emergency basis.

Contractors can help commercial and industrial customers by encouraging them to plan motor replacements instead of tackling them one at a time. By planning, customers can avoid the inconveniences of unexpected downtime, and can take immediate advantage of savings that result from higher efficiency motors.

Contractors themselves can benefit from being able to plan this service work at a time when their businesses might otherwise be slow, keeping employees busy and smoothing out some of the seasonal peaks and valleys. Their businesses also benefit because they have partnered with their customers in a matter of no small importance: equipment up time.

One valuable resource for HVACR contractors is “Motor Decisions Matter,” a campaign for motor replacement with a Web site (www.motorsmatter.org) chock-full of useful information.

According to Motor Decisions Matter, the campaign was formed “because few customers were taking the time to evaluate common motor-related decisions, such as repairing, replacing, or sizing their motors.

“For instance, according to the U.S. Department of Energy (DOE), only 12 percent consider the lower energy operating costs of new motors. As a result, few customers were demanding premium-efficiency motors or specifying quality repairs, even though these choices could save time, energy, and money for their plants and facilities.”

The coalition is made up of motor manufacturers, service centers, electric utilities, and government agencies. Their goal: “Raise customer awareness, provide a common message, and draw from a common set of resources when discussing motor efficiency opportunities with customers.”

The Web site “provides links, tools, and resources to assist motor professionals develop sound motor plans.”

According to Motor Decisions Matter, planning is the key to taking optimum advantage of motor replacements en masse. Here are some of the questions and answers posed at the site:

Question: What should be taken into consideration when deciding whether to repair a failed motor or purchase a new one?

Answer: Your local repair firm/distributor can assist you in developing a customized motor plan that makes sense to your company. A motor management plan should contain a written set of criteria for repair/replace decisions, stipulate decisions in advance on specific critical applications, or outline a repair/replace decision for each motor in the inventory and list all spares that can be used for different applications.

Question: What is the average cost difference between a standard-efficiency motor and one classified as premium efficient?

Answer: The incremental price difference between standard- and premium-efficiency motors varies by motor size, type, and availability. In some cases, premium motors can be 20 percent to 30 percent more expensive, but the additional costs of buying premium efficiency motors need not be large. Data from DOE’s MotorMaster+® database indicates that some premium-efficiency motors are now available for the same price or less than the price of typical standard-efficiency motors.

Since most motors are obtained at a substantial discount from retail (which is the cost listed in MotorMaster+), the cost increment can be even less. In many cases, the incremental cost of a premium-efficiency motor is insignificant compared to the amount of energy costs the motor will save in the long run.

Question: How can I calculate my potential energy savings by using a motor management plan?

Answer: A variety of tools are available to help you calculate the energy savings of premium-efficiency motors and quality repair services. Your local distributor, repair center, or utility representative will have the experience and information needed to help you make these calculations.

Campaign sponsors plan to offer an energy savings calculator to help customers answer this very question.

The campaign’s Web site offers information about the campaign, naturally, and links to sponsors’ Web sites. It also offers an online motor management and planning kit. The kit includes: