NovaTorque Brushless Permanent Magnet Motor Field Test Report

Transcription

1 NovaTorque Brushless Permanent Magnet Motor Field Test Report Submitted to: Sacramento Municipal Utility District May 21, 2014 Prepared by: ADM Associates, Inc Ramos Circle Sacramento, CA The information in this report is provided by SMUD as a service to our customers. SMUD does not endorse products or manufacturers. Mention of any particular product or manufacturer in this report should not be construed as an implied endorsement.

2 TABLE OF CONTENTS 1. Executive Summary Introduction Methodology Results Conclusion Appendix...12 About the Customer Advanced Technologies Program" SMUD s Customer Advanced Technologies (C.A.T.) program works with customers to encourage the use and evaluation of new or underutilized technologies. The program provides funding for customers in exchange for monitoring rights. Completed demonstration projects include lighting technologies, light emitting diodes (LEDs), indirect/direct evaporative cooling, non-chemical water treatment systems, daylighting and a variety of other technologies. For more program information, please visit: LIST OF FIGURES Sacramento Municipal Utility District i

3 List of Figures Title Page Figure 1: The NovaTorque PremiumPlus+ Brushless Permanent Magnet Motor and Exploded View... 4 Figure 2: NovaTorque Motor Nameplate Figure 3: Induction Motor Name Plate... 5 Figure 4: Side-by-Side Fans Used for Test, NovaTorque Motor in Background... 6 Figure 5: Motor kw versus VFD Percent Speed for Both Fans Figure 6: Motor kw versus Airflow Rate for Both Fans Figure 7: Flow Measurement Area of the Exhaust Fan Air Handler Damper List of Tables Title Page Table 1: Summary Results... 2 Table 2: Pre and Post Motor Swap Power Averages... 8 Table 3: Weather and Return Air Data... 8 Table 4: Pre and Post Motor Swap VFD and Airflow Rates... 9 Table 5: Normalized Results... 9 Table 6: Air Velocity (ft/min) Measurements: Induction Motor 100% Speed Table 7: Air Velocity (ft/min) Measurements: Induction Motor 80% Speed Table 8: Air Velocity (ft/min) Measurements: Induction Motor 60% Speed Table 9: Air Velocity (ft/min) Measurements: NovaTorque Motor 100% Speed Table 10: Air Velocity (ft/min) Measurements: NovaTorque Motor 80% Speed Table 11: Air Velocity (ft/min) Measurements: NovaTorque Motor 60% Speed Table 12: Air Velocity (ft/min) Measurement Averages Table 13: Air Flow (cfm) Measurement Averages Table 14: Air Flow (cfm) Trended from BMS System Table 15: Percent Differences Between Measured and BMS System Flow Rates Table 16: Stroboscope Measurements of Motor Speed (RPM) Sacramento Municipal Utility District ii

4 1. Executive Summary ADM Associates, Inc., conducted an evaluation of a new high efficiency motor for the Sacramento Municipal Utility District (SMUD). SMUD funded the evaluation through its Customer Advanced Technologies (CAT) program. In this case, the goal was to evaluate the second generation of a brushless permanent magnet motor, conventionally known as an Electronically Commutated Motor (ECM), developed by NovaTorque, Inc. ADM previously performed a bench test study of a NovaTorque 3 horsepower (hp) PremiumPlus+ Motor, while this report presents the methodology and results of a field study of a NovaTorque 5 hp PremiumPlus+ Motor in a variable speed fan application. NovaTorque claims that these new motors save more energy than National Electrical Manufacturers Association (NEMA) Premium Efficiency induction motors, with increased percentage savings in variable-speed and part-load applications. As stated by NovaTorque, the reasons for this energy usage reduction are: 1. Permanent magnets supply the magnetic field in the rotor; energy is not required to create the rotor magnetic field as it is with induction motors. 2. The axial field poles use grain-oriented steel laminations, resulting in low eddy-current energy losses. 3. The motor winding is very compact with no end-turns, resulting in low current induced energy loses. The field study was conducted comparing the NovaTorque motor to a high efficiency induction motor in a side by side field test comparison. The study was organized as follows: two 5 hp motors with variable frequency drives (VFD) served fans operating in parallel in an air handling exhaust application. One of the conventional motors was replaced with a NovaTorque PremiumPlus+ Motor. Power monitoring of each motor VFD combination was conducted in conjunction with the site s Building Energy Management System (BMS) monitoring air flow rates of each fan. The resulting data were normalized to the volume of air flow and used to calculate energy use associated with the two motor systems. After one month of monitoring, the two motors were swapped and monitored for an additional month in order to compensate for any instrumentation accuracy variables operational differences. The NovaTorque motor showed an 8.5 percent reduction in demand (Table 1) when compared directly to the induction motor. The demand normalized to airflow showed a savings of 8.7 percent in average W/cfm. Savings in other applications may vary as the average speed and speed range vary. The estimated annual energy use dropped from 4,104 to 3,754 kwh, an 8.5 percent savings. Airflow measurements were taken, and the BMS airflow monitoring was independently verified. RPM measurements were then taken for comparison with the VFD display readouts; differences between the two readings were negligible. Further discussions of these items are included in the appendix of this report. Sacramento Municipal Utility District 1

5 Table 1: Summary Results Induction Motor NovaTorque Motor Difference % Reduction Average Demand, kw % Average airflow rate, cfm 4,355 4, % Normalized Demand, W/cfm % Estimated Annual Energy, kwh 4,104 3, % As shown by this case study, NovaTorque PremiumPlus+ Motors can save energy and lower demand. The PremiumPlus+ Motors have been tested and verified by NovaTorque to be compatible with selected types of VFDs. Prior to using a NovaTorque motor you should confirm with NovaTorque the compatibility of the VFD that will be used. Sacramento Municipal Utility District 2

6 2. Introduction 2.1 Background ADM Associates, Inc., conducted an evaluation of a new high efficiency motor for the Sacramento Municipal Utility District (SMUD). SMUD funded the evaluation through its Customer Advanced Technologies (CAT) program. In this case study, the goal was to conduct field testing and evaluate the second generation of a brushless permanent magnet motor (conventionally known as an Electronically Commutated Motor) developed by NovaTorque, Inc. (see Figure 1). The NovaTorque PremiumPlus+ Motor must be paired with a qualified variable frequency drive (VFD) to optimize savings. The NovaTorque PremiumPlus+ motor s performance as an energy efficiency technology was previously evaluated by ADM using laboratory testing, and is currently being analyzed further in this field study. NovaTorque has expanded the range of ECM motors to include 2, 3, 4, 5, 7.5 & 10 hp motors. NovaTorque claims that these new motors save more energy than National Electrical Manufacturers Association (NEMA) Premium Efficiency induction motors, with increased percentage savings in variable-speed and part-load applications. As stated by NovaTorque, the reasons for this energy usage reduction are: 1. Permanent magnets supply the magnetic field in the rotor; energy is not required to create the rotor magnetic field as it is with induction motors. 2. The axial field poles use grain-oriented steel laminations, resulting in low eddy-current energy losses. 3. The motor winding is very compact with no end-turns, resulting in low I²R energy loses. Figure 1 illustrates the motor and its various components, and NovaTorque supplied ADM with the following description of its motor technology: 1 The rotor in the NovaTorque motor design consists of a pair of conical hubs mounted on opposite ends of the motor shaft. The rotor hubs use an interior permanent magnet (IPM) arrangement which provides magnetic flux concentration. An IPM design has both mechanical and adhesive magnet retention, which allows for higher speed motor operation than a surface permanent magnet design. The surface area available for magnetic flux transmission is maximized by giving the motor s stators and rotor hubs matching conical shapes. By making the rotor/stator surface area interface twice with the perpendicular cross-sectional area of the stator field pole, the motor s geometry also concentrates the magnetic flux density. The NovaTorque motor uses an axial flux path which flows straight (parallel to the shaft) through the axially-oriented field poles of the stator. The straight flux path enables the use of grain-oriented steel laminations which significantly lowers eddy-current losses in the steel. The axial orientation of the NovaTorque motor stator field poles allows the use of bobbin-wound coils (which creates a thermal path) as one face of the coils is next 1 The description has been summarized by ADM for this report. Sacramento Municipal Utility District 3

7 to the external motor case, instead of being inside the lamination stack as is found in an induction motor. The bobbin coil winding has no end-turns, resulting in lowered I²R energy losses. Figure 1: The NovaTorque PremiumPlus+ Brushless Permanent Magnet Motor and Exploded View 2.2 Assessment Objectives The goal of this study was to determine the case specific energy savings associated with the application of a 5 HP NovaTorque ECM motor in place of a standard induction motor in one of SMUD s air handling systems. Savings were evaluated for energy and demand, and were normalized to air volume flow. These findings are presented as a resource that can be used to help inform and shape future energy efficiency programs by understanding efficiency differences between the performances of ECM motors compared to common induction motors. Sacramento Municipal Utility District 4

8 3. Methodology The energy savings potential of the NovaTorque motor was evaluated using a side by side test of 5 hp air handler motors operated by identical variable frequency drives in a real building application. The test procedure called for four weeks of data collection with the motors in each position. The NovaTorque is a permanent magnet motor (Figure 2), while the comparison motor was an existing premium efficiency induction motor (Figure 2). Figure 2: NovaTorque Motor Nameplate Figure 3: Induction Motor Name Plate The two fans used for this study are located in a SMUD shop building (see Figure 4). These fans run in parallel on the top deck, drawing exhaust air across heat recovery coils into a common chamber and pushing the air into a common duct. Metrics were collected to normalize motor energy use to air flow rates using the Building Energy Management System (BMS). After the first four weeks of data collection, SMUD swapped the positions of the two motors and collected data for another four weeks. The purpose of swapping motor positions was to switch the power and air flow sensors in order to account for any difference in accuracy between the sensor systems or any non-symmetry. Prior to the test the VFD s were replaced by (ABB ACS355) VFDs widely used for control of induction motors and also compatible with NovaTorque motors. Sacramento Municipal Utility District 5

9 Figure 4: Side-by-Side Fans Used for Test, NovaTorque Motor in Background The following is the list of BMS trend points that were collected at one minute intervals for the analysis: 1. Exhaust Air flow CFM, Fan 1; 2. Exhaust Air flow CFM, Fan 2; 3. Total Exhaust air flow, CFM; 4. Target Exhaust air flow, CFM; 5. Exhaust air temperature in fan chamber; 6. Percent Speed, frequency, or RPM of Fan 1; 7. Percent Speed, frequency, or RPM of Fan 2; 8. Fan power, kw, Fan 1 (reported by VFD); 9. Fan power, kw, Fan 2 (reported by VFD); 10. Drive input voltage, Vac, Fan 1; 11. Drive input voltage, Vac, Fan 2; 12. Drive input current, Amps, Fan 1; and 13. Drive input current, Amps, Fan 2. In addition to the data provided by the BMS, ADM independently monitored and collected power use data. Two WattNode watthour meters (model WNB-3D-480-P) were placed inside the VFD enclosure, one for each fan motor. The WattNode power accuracy rating is ±0.5% at 5% to 100% of full scale. The WattNodes require a current sensor input. High-accuracy split-core current transducers (CTs) were used which have an accuracy of ± 0.5% from 1% to 100% of full scale. The CTs have a 20 amp full scale primary rating. These meters measure three-phase 480 V loads and produce a pulse output that is proportional to the energy the load uses. The pulse output from the WattNode meter was connected to a battery operated Hobo pulse logger (model UX90-001M), and recorded energy use in 1-minute intervals. Sacramento Municipal Utility District 6

10 Independent air flow measurements were also conducted for the two fans by using a hot wire anemometer to take a matrix of air speed measurements in front of the louvered fan intake. The model used was the TSI VelociCalc Plus with an air speed range from 0 to 9999 feet per minute (ft/min) and an accuracy of ± 3% of reading or ±3 ft/min, depending on whichever is greater; the resolution is 1 ft/min and the instrument has a response time of less than one second. The sensor is on a 40 inch telescoping probe. At the time of the air flow measurement, the SMUD BMS operator set the fans to fixed speed settings for several minutes as air flow measurements were being made. Three fixed fan speeds were used for air flow measurements, 60%, 80%, & 100% speed, which represent the typical range of operation. The airflow results are discussed in the appendix of this report. Temperature and humidity data were also collected in order to identify any relationships between fan operation and weather data, allowing for normalization of monitored savings to a typical year. One time measurements of motor RPM (revolutions per minute) were also taken using a stroboscope. The RPM test results are discussed in the appendix of this report. Sacramento Municipal Utility District 7

11 4. Results Monitoring occurred during the period from October 30th to February 14th. The motor position was swapped on January 16th, meaning that the monitoring period prior to the motor swap was twice as long as the period after the swap. Issues with trend log consistency suggested that most of the November data would not be used. The post period is the limiting factor when selecting comparable pre and post periods for analysis. Equal weighting for pre motor swap and post motor swap averages was achieved by using an equal number of monitoring days from both periods. The total number of monitoring points varies by day because the system is set up to trend only when the motors are in operation, which roughly follows the work schedule. The pre- and post-motor swap monitoring periods both spanned four weeks. The eight week average motor power draw for the induction motor was 1.09 kw while the NovaTorque average draw was 1.00 kw. The average demand was reduced by 0.09 kw or 8.5 percent. Average demand for the pre- and post- motor swap periods are shown in Table 2. Table 2: Pre and Post Motor Swap Power Averages Induction Motor NovaTorque Motor Difference % Reduction Pre Motor Swap Average, kw % Post Motor Swap Average, kw % Average Demand, kw % The average savings in the two motor positions is an accurate representation of the monitoring period conditions for the two fan motor positions. Next we compared the pre-swap and postswap periods under several conditions in order to demonstrate their similarity to each other. The outside temperature conditions when the fans were running and trend data were available averaged 53 ºF with a range of 32 to 79 ºF as can be seen in Table 3. The average outside temperature during fan operation for the pre-swap period was 51.4 ºF while the post-swap period averaged 54.2 ºF. During the post-swap period, the outside air temperature averaged 2.8 ºF warmer and the return air temperature averaged 2.9 ºF warmer. Table 3: Weather and Return Air Data Pre-Swap Post-Swap Both Periods Average Outside Temperature, ºF Min. Outside Temperature, ºF Max. Outside Temperature, ºF Standard Deviation, ºF Average Return Air Temp, ºF Swapping the motors allowed variations in the flow sensors and position symmetry to be averaged out by operating the fan motors for the same amount of time in each position. The BMS is setup so that the VFDs provide equal set speeds for the NovaTorque and the induction Sacramento Municipal Utility District 8

12 motors. Data comparing the VFD and airflow rate conditions for the pre- and post-motor swap periods are provided in Table 4. The average pre-swap period VFD speed was 68.4 percent while the post-swap period VFD speed was 71.8 percent. The fan speeds were similar across both periods, but averaged 3.4 percent faster during the post-swap period. The airflow rates were also higher for the post-swap period. The airflow rate was used to normalize the motor energy use. The average airflow rate of the NovaTorque driven fan was 0.7% higher than the induction motor driven fan. With the average VFD speed around 70 percent, the amount of motor slip on the induction motor is expected to be less than if the motor is operating at full speed or is more heavily loaded. Table 4: Pre and Post Motor Swap VFD and Airflow Rates Induction Motor NovaTorque Motor Difference % Reduction Pre-Swap airflow rate, cfm 4,344 4, % Post-Swap airflow rate, cfm 4,365 4, % Average airflow rate, cfm 4,355 4, % Pre-Swap VFD Speed, % % Post-Swap VFD Speed, % % Average VFD Speed, % % The average power savings during the monitored period was 8.5%, which equates to 0.09 kw. These values were then normalized to the amount of airflow drawn by the fan motors. The normalized results are provided in Table 5 and show that the average normalized savings increased slightly to 8.7 percent. The normalized power per airflow volume was W/cfm for the induction motor and W/cfm for the NovaTorque motor. The savings are expected to vary, by an unknown amount, during other seasons. The system only runs during the work day, which eliminates a majority of night time and weekend operation. Although savings cannot be reliably annualized without addition seasonal operating data, Table 5 displays a projection as if the conditions are the same throughout the year. This provides a magnitude of the annual energy use and savings. The estimated annual energy use dropped from 4,104 kwh for the induction motor to 3,754 kwh for the NovaTorque motor, an 8.5 percent savings. Table 5: Normalized Results Induction Motor NovaTorque Motor Difference % Reduction Average Demand, kw % Average airflow rate, cfm 4,355 4, % Normalized Demand, W/cfm % Estimated Annual Energy, kwh 4,104 3, % Sacramento Municipal Utility District 9

13 Presentation of the motor fan power curve data for both motors versus VFD percent speed and airflow are provided in Figure 5 and Figure 6 respectively. Eight weeks of pre- and postswapping data are included. 3.0 kw Induction Motor, kw NovaTorque, kw Power (Induction Motor, kw) Power (NovaTorque, kw) y = x R² = y = x R² = VFD % Speed Figure 5: Motor kw versus VFD Percent Speed for Both Fans Induction Motor, kw NovaTorque, y = x kw R² = Power y = (Induction x Motor, kw) R² = Power (NovaTorque, kw) kw CFM Figure 6: Motor kw versus Airflow Rate for Both Fans Sacramento Municipal Utility District 10

14 5. Conclusion The findings presented in this report indicate that the NovaTorque PremiumPlus+ motor has the potential to save energy in variable speed applications where it supplants a typical NEMA Premium efficiency induction motor. The NovaTorque motor system maintained more efficient operation in a real building, variable speed application than did the NEMA Premium induction motor. When evaluated in an in-situ study, the NovaTorque motor showed 8.5% savings when compared to a Premium Efficiency induction motor, with normalized power demand savings of 8.7%. Sacramento Municipal Utility District 11

15 6. Appendix Air flow measurements were taken using a TSI VelociCalc Plus flow meter. Initially a 126 measurement point distribution was initiated to calculate the flow profile of the fan. Conducting this test verified that a 24 point distribution would accurately represent the flow profile. Measurements were taken in the 24 point pattern for each fan at 60% flow, 80% flow, and 100% flow. These flow measurements were verified with the systems BMS trending. Velocity measurements were taken in units of feet/minute (ft/min) which were then converted to flow (CFM) by taking the average of the velocity points across the damper and multiplying it by the area of the damper (32.5 inches x 32 inches). Table 6: Air Velocity (ft/min) Measurements: Induction Motor 100% Speed Right Side: Induction Motor 100% Start: 9:36 End 10:18 left side (approx. 1" from the edge) 5 in 10 in middle 20 in 25 in right side (approx. 1" from the edge) 1-line (top) gap line gap line gap line thin gap bar thin gap line gap line gap line gap line gap (bottom) Sacramento Municipal Utility District 12

16 Table 7: Air Velocity (ft/min) Measurements: Induction Motor 80% Speed Right Side: Induction Motor 80% Start: 11:28 End 11:35 left side (approx. right side (approx. 1" from the edge) middle 1" from the edge) 1-gap gap gap bar gap gap gap gap Table 8: Air Velocity (ft/min) Measurements: Induction Motor 60% Speed Right Side: Induction Motor 60% Start: 11:05 End 11:27 left side (approx. right side (approx. 1" from the edge) middle 1" from the edge) 1-gap gap gap bar gap gap gap gap Table 9: Air Velocity (ft/min) Measurements: NovaTorque Motor 100% Speed left side: Nova Torque 100% Start: 10:24 End 11:45 left side (approx. right side (approx. 1" from the edge) middle 1" from the edge) 1-gap gap gap bar gap gap gap gap Sacramento Municipal Utility District 13

17 Table 10: Air Velocity (ft/min) Measurements: NovaTorque Motor 80% Speed Left Side: Nova Torque 80% Start: 11:36 End 11:45 left side (approx. 1" from the edge) Middle right side (approx. 1" from the edge) 1-gap gap gap bar gap gap gap gap Table 11: Air Velocity (ft/min) Measurements: NovaTorque Motor 60% Speed Left Side: Nova Torque 60% Start: 10:46 End 11:04 left side (approx. 1" from the edge) middle right side (approx. 1" from the edge) 1-gap gap gap bar gap gap gap gap Table 12: Air Velocity (ft/min) Measurement Averages Induction NovaTorque 60% % % The system averages were taken and then multiplied by the damper area to obtain CFM. The results are shown in Table 13. Table 13: Air Flow (cfm) Measurement Averages Induction NovaTorque 60% 3,898 4,195 80% 5,419 5, % 7,368 7,354 Sacramento Municipal Utility District 14

18 The BMS system flow measurements were trended during the measuring period. The resulting CFM measurements are shown in Table 14. Table 14: Air Flow (cfm) Trended from BMS System Induction NovaTorque 60% 3,756 3,624 80% 5,116 4, % 6,522 6,249 The measurement differences between the one time measurements and the system BMS measurements show a 4% to 18% difference, with all instances showing the one time measurements recording higher flow rates than the BMS recording (Table 15). Table 15: Percent Differences Between Measured and BMS System Flow Rates Induction NovaTorque 60% 104% 116% 80% 106% 109% 100% 113% 118% There are two reasons for these differences. First, there is some variability to the damper area. The measurements were calculated using the length times the width, but there are several damper veins obstructing the flow path and creating a smaller effective area (Figure 7). Additionally, the VelociCalc flow meter has an accuracy of ± 3%. Due to these differences, the BMS measurements are the preferred method of flow metering as they are permanently in place and continually logging airflow data. Sacramento Municipal Utility District 15

19 Figure 7: Flow Measurement Area of the Exhaust Fan Air Handler Damper Motor Speed measurements were taken in units of RPM and compared to the VFD display readout. Measurements were taken at 50% speed and 100% speed. The goal was to see if any effects from reduced rotational slip of the NovaTorque motor could be picked up by comparing the measured speed with the VFD speed setting. It was hypothesized that when the VFD was set to the 1800 RPM max, the NovaTorque would function at exactly 1800 RPM while the induction motor would show operation at fewer RPMs because of slip. The results (Table 16) showed a scenario similar to the expected, however the difference between the NovaTorque RPM and the Induction Motor RPM shows only a.2% difference at full speed, and even less of a difference at half speed. Table 16: Stroboscope Measurements of Motor Speed (RPM) Pre-swap Post-swap Stroboscope Reading VFD Panel Reading 50% 100% 50% 100% NovaTorque Induction NovaTorque Induction Sacramento Municipal Utility District 16