Swapping ECM for PSC fan motor
I know a homeowner who runs the fan on his Ruud UBHC-17J11NFD air handler (2.5 ton heat pump) continuously in the summer to help keep the temperature a bit more consistent between the upstairs and downstairs, so he figures swapping the OEM PSC fan motor for an ECM motor, such as the Evergreen, might pay for itself.
The Evergreen mfr/distributor says the following:
“No stock catalog replacement motor is an exact replacement for an OEM Factory Authorized part, standard stock PSC motor or ECM motor. It’s the contractor’s job to ensure proper airflow to meet cooling or heating needs as required for the OEM equipment, and ensure that can be achieved when replacing an OEM motor with a generic replacement motor.
The OEM body of motor in this system is 4.48″ long with a 3.25″ shaft.
The Evergreen AH, which would be my best recommendation for an ECM replacement, pending fit, is 5.75″ long with a 5″ shaft.
Both motors are standard 48 Frame (5.6″) diameter motors.
Many Rheem systems also have special Rheem mounting brackets that would not work with an Evergreen, the contractor would need to get a standard torsion flex or wire form mount to install the motor.
Your contractor is the best person to determine mechanical fit.
The Evergreen AH Model #6001 is the 1/2Hp CCW rotation (same rotation as the OEM motor). The lower 2 or 3 speed selections would be tried (5 available on the AH ) by the contractor to match the airflow of this OEM 2 speed 1/4Hp motor.”
The homeowner’s contractor says, “I don’t know what the savings would be versus the expense to install this motor. I don’t think there are any savings, unless this is used as a variable speed motor which would require variable speed controls.”
So my questions are:
1) Is it even physically possible to swap these motors, and
2) How soon, if ever, would the new ECM pay for itself?
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Bear with me -- my answers will be long. I'll post two articles I have written on the topic.
The first article addresses replacement motors for air handlers and furnaces. The article, "Retrofit Motors That Mimic ECMs," originally appeared in the November 2008 issue of Energy Design Update. Here's the article:
Electronically commutated motors (ECM) are much more efficient than permanent split capacitor (PSC) motors, especially at low speeds (see EDU, August 1995). An ECM is a variable-speed permanent magnet brushless DC motor paired with a programmable control. ECMs were originally developed by General Electric, which trademarked the term “electronically commutated motor.” Regal Beloit, a motor manufacturer in Beloit, Wisconsin, now holds the license to manufacture ECMs.
Compared to a conventional furnace, a furnace with an ECM-equipped blower can save significant amounts of electricity, especially in homes with electronic air filters or ventilation protocols that require the furnace fan to run continuously. “When GE introduced the ECM, the key development was not the motor but the control mechanism,” explains John Proctor, a well-known air conditioning consultant and the president of Proctor Engineering Group in San Rafael, California. “GE worked with the furnace manufacturers to develop controls that provide a constant cfm under varying conditions.”
Unfortunately, most residential furnaces and air handlers are sold with inefficient PSC blower motors. Until recently, anyone interested in purchasing a furnace with an ECM-equipped blower had few choices, since the option was available only in top-of-the line models with an upcharge of $1,000 or more.
Now, however, two motor manufacturers have developed ECM-mimicking motors designed for retrofit installation in almost any residential furnace or air handler. One of the two new motors, the Evergreen IM, is manufactured by Regal Beloit, the current manufacturer of ECMs. The other motor, the Concept 3 from McMillan Electric, was developed in consultation with John Proctor.
Although neither motor provides one of the touted (but questionable) benefits of an ECM – the ability to maintain a constant airflow under changing conditions – they promise to be easy to install, energy-efficient, and significantly cheaper than a replacement ECM. Anyone who wants a furnace with ECM-like performance can now purchase an inexpensive furnace and replace the manufacturer’s inefficient PSC motor with a new retrofit motor.
The Evergreen IM Motor
Regal Beloit’s Evergreen IM is a dual-voltage (120 and 240 volt) motor that is compatible with virtually all residential furnaces and air handlers (see Figure 3). The Evergreen IM is a variable-speed, permanent magnet brushless DC motor – the same type of motor used in furnaces equipped with an ECM. “This is not new technology,” said Christopher Mohalley, master ECM trainer at Regal Beloit. “The only difference between the Evergreen and an ECM is in the computer – we’ve changed the program so that it can be applied to a retrofit system.”
ECM-equipped blowers are programmed to provide a constant airflow in spite of changing circumstances – for example, to handle an increasingly dirty filter. “Variable-speed ECMs are programmed by the HVAC manufacturer,” explained Mohalley. “They are ‘taught’ at the factory by Carrier or Lennox or whoever. With a retrofit motor, we don’t know which furnace it’s being put into, so we had to make the motor more generic. As static pressure goes up, the Evergreen will produce less airflow. We are not promoting it as a constant-airflow motor, because it isn’t one.”
For those interested in energy efficiency, however, the constant-airflow feature of an ECM is relatively unimportant. The way that an ECM maintains a constant airflow is by increasing the motor’s horsepower output (and watt draw) in response to rising static pressure; this feature increases, rather than decreases, energy use. Moreover, according to one recent study (“Central Air Conditioning in Wisconsin,” Energy Center of Wisconsin, 2008), many small air conditioners are set up with too much airflow; lower airflows, therefore, have the potential to improve efficiency.
Choose Your Horsepower
The installer of an Evergreen IM motor can choose its horsepower output. “There are two Evergreen models – a ½ -horsepower and a 1-horsepower model,” said Mohalley. “You can configure either motor at three different horsepower levels. For example, if you are replacing a 1/3-horsepower motor, you would use the ½ -horsepower model, and configure it to run at 1/3 horsepower.”
Brushless DC motors are inherently more efficient than PSC motors. “The Evergreen motor runs at 80% efficiency compared to 60% efficiency for a PSC motor,” claimed Mohalley. “So it’s always going to be more efficient than a PSC. When it comes to controlling the Evergreen, the only way to use less energy is to run the motor slower. The good thing is, when you slow down the motor, its efficiency doesn’t drop.”
The Evergreen motor’s biggest efficiency benefit will occur in homes where the furnace fan runs around the clock. “When used in ‘constant fan’ mode, at low speed, the motor draws 100 watts or less – maybe 95 watts,” said Mohalley. “And the airflow is very quiet.”
Regal Beloit declined to provide EDU with information on the price of the Evergreen IM.
The Concept 3 Motor
John Proctor has worked with McMillan Electric, a motor manufacturer in Woodville, Wisconsin, to develop an ECM-mimicking retrofit motor called the Concept 3 (see Figure 4). The Concept 3 is inexpensive, energy-efficient, and compatible with most residential furnaces and air handlers.
Like the Evergreen IM, the Concept 3 is a permanent magnet brushless DC motor. According to Proctor, the motor comes with complete instructions and is easy to install. “First you measure the watt draw of the old motor,” said Proctor. “Then you measure the static pressure in the supply plenum with the old motor running. PSC motors are usually set up with a cooling speed and a heating speed. In 95 percent of standard furnaces, there are four speed taps coming off the motor: high speed, medium high speed, medium speed, and low speed. The cooling speed is usually high speed, while the heating speed is usually medium high or medium.
“The speed of the Concept 3 motor is infinitely variable. Once the new motor is installed, you adjust the motor speed to get the same airflow as the original motor. The adjustment is based on the static pressure in the supply plenum – you adjust the motor to achieve the same static pressure. What the adjustment does is change the horsepower output of the motor. It’s a one-time adjustment. At that point you measure the new watt draw to verify the energy savings.”
Proctor warns installers to avoid the temptation to increase airflow. “Our research now shows that increasing airflow is often not a good idea,” said Proctor. “So it’s best to go with what you’ve got.”
Like the Evergreen IM, the Concept 3 is not a constant-airflow motor. Proctor explained, “There is no feedback, so if restrictions happen in the duct system or filter, the static pressure goes up, airflow goes down, and the watt draw will remain the same.”
Improved Cooling Efficiency
The Concept 3 uses line voltage connections for power and 24-volt signal wires to the furnace terminal block for speed selection. The controls are highly sophisticated. “The highest speed is for cooling,” said Proctor. “For dry climates, the Concept 3 control directs the fan to continue running at the end of the cooling cycle, at a much lower speed and watt draw, to evaporate the water off the coil, providing increased sensible efficiency. If you live in a wet climate, the 24-volt signal wires are hooked up differently so that you get a lower top speed, which provides more dehumidification in cooling mode. In a wet climate, the fan goes off at the end of the compressor cycle, allowing the coil to drain. If the thermostat is set to ‘constant fan’ – in homes with constant ventilation or filtration equipment – the fan still shuts down at the end of the compressor cycle so the coil can drain, and only comes back on after a 20-minute wait.
“If you live in a climate where it is sometimes dry and sometimes wet, you need to install an indoor Thermidistat. The motor controls will then switch from dry climate programming to wet climate programming, depending on the indoor conditions.”
Lower Electricity Use
The Concept 3 motor uses significantly less electricity than a comparable PSC motor. “The Concept 3 has a much lower watt draw for the same cfm,” claimed Proctor. “At the lowest speed, it draws between 60 and 100 watts. In a dry climate, the biggest energy savings come during cooling mode, because of the control which runs the motor at a very low speed at the end of the compressor cycle. The additional sensible capacity provided by that feature amounts to an energy saving of about 12 to 20 percent, in addition to the 8 percent saving attributable to the improved efficiency of the motor.”
According to Proctor, the Concept 3 “is compatible with all equipment except the Carrier Infinity series, which doesn’t use a standard 24-volt signal.” The motor is being distributed by Energy Federation Incorporated in Westborough, Massachusetts. “The price to the contractor is less than $200,” said Proctor. “That’s compared to $800 to $1,200 for an ECM with the control board.”
For more information, contact:
Energy Federation Incorporated (EFI), 40 Washington Street, Suite 3000, Westborough, MA 01581. Tel: (800) 876-0660 or (508) 870-2277; Fax: (508) 870-9933; E-mail: [email protected]; Web site: http://www.efi.org.
Evergreen Sales, 1946 West Cook Road, Fort Wayne, IN 46818. Tel: (866) 503-8566; Fax: (260) 416-5499; E-mail: [email protected]; Web site: http://www.evergreendealer.com.
McMillan Electric, 400 Best Road, Woodville, WI 54028. Tel: (715) 698-7119; Fax: (715) 698-2297; Web site: http://www.mcmillanelectric.com.
Regal Beloit, 200 State Street, Beloit, WI 53511. Tel: (608) 364-8800; Fax: (608) 364-8818; Web site: http://www.regal-beloit.com.
The second article, "Improvements in Fan Motor Efficiency Could Yield Big Savings," originally appeared in the March 2003 issue of Energy Design Update. Here it is:
Because the annual fuel utilization efficiency (AFUE) calculation for furnaces considers only fossil-fuel use, not electricity use, fan motor efficiency receives little attention from furnace manufacturers. Moreover, air conditioner manufacturers have little incentive to improve fan motor efficiency, since the existing seasonal energy efficiency ratio (SEER) test protocol includes default values for fan motor power consumption that differ from actual fan motor current measured in field studies.
“Residential HVAC Fans and Motors Are Bigger than Refrigerators,” a paper presented at the 2002 ACEE Summer Study on Energy Efficiency in Buildings, examines the economics of improvements in furnace fan motor efficiency. Authors Harvey Sachs, Toru Kubo, Sandy Smith and Kalon Scott note that electronically commutated motors (ECMs) are 15% to 30% more efficient at high speeds than permanent split capacitor motors (the type of motor installed in 90% of all residential air handlers). At low speeds, ECMs are even more impressive, achieving twice the efficiency of permanent capacitor motors.
The study’s authors note that investments in improved fan motor efficiency will yield greater energy savings than investments in further AFUE improvements. Although most furnace manufacturers offer ECMs for only their top-of-the-line equipment, ECMs are cost-effective in all regions of the country, with a payback period varying from two to three years (see Table 2). Switching to an efficient fan motor would save the typical homeowner 790 kWh per year, more than the consumption of a 2001-compliant refrigerator. But, in the absence of a regulatory nudge from Washington, furnace manufacturers show little interest in making ECMs available to all furnace buyers.
The study is included in the 2002 ACEE Summer Study on Energy Efficiency in Buildings, available on CD-ROM for $115 from American Council for an Energy-Efficient Economy, 1001 Connecticut Avenue, NW Suite 801, Washington, DC 20036. Tel: (202) 429-8873; Fax: (202) 429-2248; E-mail: [email protected]; Web site: http://www.aceee.org.
Martin, fantastic info, thank you!
Martin, you've outdone yourself. Thank you again.
Thanks for the great answer, Martin. But I was hoping for the kind of savings you see by swapping fluorescent for incandescent. If I read your articles right, the efficiency improvement is only about 20%. And there seems to be a good bit of confusion about how compatible the retrofit ECM's really are with OEM, at least on Evergreen's end. Do any of the mfr's you listed have total confidence that their ECM's will be compatible with a specific air handler?
You should contact the manufacturers of replacement motors to discuss your plan.
Of course, payback depends on many factors: the cost of the motor, the cost to install the motor, the cost of the homeowner's electricity, and the number of hours per year that the blower operates. It's quite possible that the payback period will be fairly long, and that you or the homeowner might decide that the proposed motor replacement isn't worth the hassle.
Martin, you mentioned John Proctor, he has some really good videos floating around somewhere on the Internet about good HVAC practices. I have them somewhere.
John Proctor knows everything there is to know about air conditioners and ducts (and probably lots of other building science topics). He's a forced-air system guru.
this may be the link you are thinking of
John Proctor Video....among many other good building science videos
Timely topic. I was about to start an ECM thread this morning...
I just audited a house with a 3 year old sealed combustion Trane furnace and a 16 SEER Trane AC. The system presumably has an ECM. Many of the ducts are 4" round, many other ducts are horribly installed flex, and system duct leakage is massive (probably over 25% of system airflow). External static pressure in the system was also very high, measured at .84 IWC.
I recall reading at one point an article that stated an ECM would actually carry with it a noticeable energy penalty if retrofitted onto a poorly configured, leaky, restrictive ducted system such as this, and that a PSC would be less expensive to operate. This makes sense to me, as the ECM would ramp up and would operate under a higher draw.
Am I off base on this??? And what if airflow was not a problem? Would an ECM have a noticeable energy penalty versus a PSC if duct leakage were the only serious problem with the duct work?
I'm well aware that, in my example, a complete overhaul of the ductwork is the only way to fix the problem.
I'm not sure of the answer to your question -- perhaps Michael Blasnik will show up soon with an answer -- but it seems to me that if the ECM blower uses more energy, it would only because it is doing a better job of delivering airflow to the duct system. If the PSC motor is using less energy, it should also be pointed out that the PSC blower isn't getting the air where it belongs.
The question is rather academic, however, since we all agree that the solution is to fix the leaky duct system.
Yes John, those are the exact videos I was referring to.
In this situation, the air ain't getting where its supposed to go regardless! If I'm going to be uncomfortable either way, I'd rather save a few bucks in the process :)
The article I had been thinking of is actually a Home Energy article by David Springer from Nov/Dec '09 titled "Is There a Downside to High MERV Filters?".
This excellent article examines electrical draws at different static pressures for both PSC and ECM motors. ECM's are unequivicolly more efficient by every metric shown in the article.
Great articles Martin, I just wanted to point out that the ACEEE study you mention, and all of their other reports, are available with free registration on their website. The referenced study is at: http://aceee.org/proceedings-paper/ss02/panel01/paper21