ELECTRONICALLY COMMUTATED MOTORS Part 2: …

1 CONSTANT-AIRFLOW, VARIABLE-SPEED (OEM)INDOOR BLOWER ECMsTheconstant-airflow(variable-speed) ECM wasintroduced in 1987 by GE (rebranded genteq in2009). It was the first and only indoor blower ECMuntil the introduction of the constant-torque ECM in2006. The term variable-speed motor was coined inthe late 1980s. By function it is a constant-airflowmotor. Both of these terms define the type or style of ECM and how it is programmed to MOTORS are built in 1 3-, 1 2-, 3 4-, and 1-hp sizes, and only in direct-drive MOTORS have gone through many generationalimprovements in their more than 20 years ofexistence, including advances in reliability andcommunication formats, as well as changes in theirphysical appearance. This chapter covers only thecurrent-generation three main benefits of these MOTORS overconventional induction (PSC) MOTORS are: increased electrical efficiency more precise and unlimited airflow selection (the variable-speed feature)1 ELECTRONICALLY COMMUTATED MOTORSPart 2: Constant-Airflow ECMsby Christopher MohalleyGenteq Certified Master ECM Trainer 2010 by the Refrigeration Service Engineers Society, Des Plaines, ILSupplement to the Refrigeration Service Engineers Application ManualSAM Chapter 650-004 Section 6A 16-pin ECM modelControl moduleMotor module4-pin ECM modelControl moduleMotor moduleFigure 1.

2 Construction of variable-speed ECMsCOURTESY OF genteq properly maintained airflow during changes insystem static pressure (the constant-airflow feature).The ECMs shown in Figure 1 on the previous pageare actually built as two separate components. Thecontrol module( motor control), with its own shell orhousing, is attached to the back of themotor module( motor ). The variable-speed motor control isprogrammed to provide constant airflow. This isaccomplished by converting the desired cfm to aspecific speed (rpm) and torque (current) delivered to the HVAC OEM (original equipment manufacturer)creates a special program unique to the model andsize unit in which the variable-speed ECM will beused. This program provides multiple airflow andcomfort options for each demand of the system inwhich the motor is installed, and any of the possibleconnected summarize: The variable-speed motor is operatedby two programs.

3 The HVAC OEM programdetermines the amount of airflow needed by demand,and the constant-airflow program makes sure that the selected airflow is maintained even if externalstatic pressure changes. The constant-airflowprogramming is unique to each OEM by model andsize of appliance. No two variable-speed MOTORS areprogrammed variable-speed ECM is a dual-voltage motor . The120-V ac or 240-V ac single-phase power is suppliedthrough the 5-pin connector to the motor at all times,even if there is no demand for airflow (see Figure 2).This power is what operates the internal electronicsand drives the motor . The low-voltage or serialcommunication that is sent to the motor from theOEM control board through the 16-pin or 4-pinconnector is a combination of the OEM programming,the installer s selection of airflow and comfort settings,and the current demand of the HVAC system (heat,cool, fan, etc.)

4 This is the information that the motorcontrol (microprocessor) requires to determine howmuch torque and speed the motor will need in orderto supply the proper airflow for each each demand, the motor control alsomonitors the actual speed in revolutions perminute (rpm) of the motor . There is only onecombination of torque and speed that willcreate the proper cfm demanded at a specifictotal ESP (external static pressure) of thesystem. If the speed/torque relationship isincorrect for the required airflow, the motorcontrol can increase or decrease the torque(current) to the motor . This, in turn, willincrease or decrease the speed of the motor to maintain airflow. By constantly monitoringthe actual speed of the motor , and maintainingthe torque/speed relationship programmed bythe HVAC OEM, the motor control is able tomaintain the airflow selection per demand ifthe total ESP very important points must beunderstood about this motor s ability tomaintain a constant airflow:2 COURTESY OF genteq 4-pinconnection5-pinconnection16-pinconn ection5-pinconnectionFigure 2.

5 Electrical connections1. The motor requires more energy tomaintain airflow when the total ESP is higher than the HVAC OEMrecommendation, and the air noise of the system may be The motor requires less energy tomaintain airflow when the total ESP is equal to or less than the HVAC OEM recommendation, and the air noise of the system will be The motor has a programmed limit ofoperation to protect itself from damage,due to the energy (current) it must use tomaintain airflow if the total ESP gets too the HVAC OEM literature to find therecommended maximum total ESP. If the systemexceeds the HVAC OEM recommendation, airflowmay not be maintained however, the motor willstill try to deliver as much air as possible, withoutcausing damage to AND BENEFITSV ariable-speed MOTORS are typically found in two-stage, multi-stage, and modulating high-end furnaces(80+% and 90+% AFUE), air handlers, packagesystems, and geothermal airflowis the ability of the variable-speedmotor to maintain its programmed and field-selectedairflow per demand, even when the total ESP ishigher than recommended and/or changes duringsystem operation.

6 The total ESP (the resistance to the movement of air) is increased when ductwork isundersized, poorly constructed, and/or full of dirt ordebris. The total ESP can increase during systemoperation when dirt builds up on the air distributionsystem components (especially the filter), and whencustomers close or block grilles and variable-speed motor is programmed to maintainairflow during all of these situations, within the limitsof the OEM programming and motor design. Bycontrast, torque (current) and airflow will decreasewhen the total ESP increases in PSC induction motorsystems (see Figure 3).When set up correctly, the benefits of the variable-speed motor system include: energy savings improved outlet air temperature for each systemdemand improved humidity control improved system capacity reduced space temperature swings reduced air noise with soft start/stop and gradualchanges between airflow demands, delays, and/orprofiles reduced constant fan air noise with low cfmsettings, plus increased energy savings overnormal system operation reduced repairs associated with continuous low-airflow AND SETUPA fter the system is installed, the technician mustfollow the HVAC OEM s instructions in selecting the proper airflow and comfort settings to match thecomponents and desired operation.

7 These settings aretypically selected by using jumper pins, dip switches,and/or multi-pin plugs on the OEM control , cfmTotal ESP, in. LOPSC MEDPSC HIFigure 3. Airflow vs. total ESPCOURTESY OF genteq (see Figure 4). There are also some systems in whichmany of these selections can be adjusted at the userinterface. (In these systems, the user interfacereplaces the thermostat as the communication centerfor the system.) If these selections are not set at thetime of installation, there is a good chance that thesystem will not perform as expected and/or notproduce the designed capacity. In addition, thesystem may be prone to problems and/or prematureparts 5 shows several examples of HVAC OEMairflow and comfort charts. Thetrim/adjust airflowchart allows the cooling airflow to be tweaked up ordown to increase the sensible or latent capability ofthe cooling system.

8 Theclimate/delay profilechartsare designed to enhance the cooling cycle by climatefor either more dehumidification or OFF-cycle comfort option that greatly enhancesdehumidification uses an external humidistat. Thehumidistat provides a demand to the HVAC systemthat is transferred to the motor to decrease the airflowduring the cooling cycle. This type of on-demanddehumidification typically requires a separatehumidistat or thermostat/humidistat combination, and a setting on the control board in the OEM systemto initiate the is recommended that the electrical connections onthe ECM be facing downward, or between the 4 and 8 o-clock positions, and a drip loop formed out of the wiring harness leaving the motor (see Figure 6).This prevents any moisture or water that may get into the motor area from running into the connectors,where it could cause damage to the control.

9 In mostsystems, the OEM installs the motor in the correctposition and provides the drip loop. However, whenmulti-position systems are installed in a positionother than the manufactured position, the motor may need to be turned and the drip loop total ESP of the installed system should bemeasured and compared to the OEM charts. If it isabove the maximum listed for that unit, improvementsshould be made to lower it. Any total ESP below themaximum is typically acceptable. However, systemefficiency, noise levels, and potential service issuesall will be improved when the total ESP is as close tothe OEM recommendation as possible. The OEM sinstallation manuals provide guidelines that shouldbe followed per unit for best performance. Someimportant examples of the guidelines found in thesemanuals include filter-sizing charts, proper ductconnections, and unit temperature rise in fossil-fuel systems shouldalways be measured and corrected if it is not withinthe OEM rating listed on the data plate of the :Water damage is one of the most frequentlyrecurring failures associated with electricalcomponents.

10 Always construct and size thecondensate drains and traps according to troubleshooting any HVAC system, it s a good practice to become familiar with the systemcomponents and wiring diagram. Check for andfollow any on-board diagnostics (OEM system faultcodes). When you re working on a variable-speed4 Rotary switchfor delay timeModel plugs forheating selectionRotary switch forcooling tonnage4352XX4352 XXDip switches34567821 ONJumper pinsHEATABCDCOOLABCDDELAYABCDADJUSTNORM( +)( )TESTF igure 4. Control board optionsCOURTESY OF genteq system, you should also check the airflow, comfort,and delay settings. Typically you will need to consultthe HVAC OEM manuals for these settings. Themanufacturer s literature can also provide valuablesequence-of-operation and troubleshooting the motor is running but the system is noisy,shutting down on its limits or safeties, or theevaporator coil is freezing, there is a good chancethat the problem is most likely external to the motorand the motor itself is good.