MICHIGAN WEA 2015 Energy Seminar October 20, 2015

Transcription

1 VARIABLE SPEED PUMP CONTROL: HOW AND WHY OF VARIABLE SPEED PUMPING MICHIGAN WEA 2015 Energy Seminar October 20, 2015 Presented by Gary Patterson Water/Wastewater Technical Sales Director DSI/Dynamatic

2 Share of motor electrical consumption Cooling Compressors Air Compressors 18% 7% 2% Conveyors 35% Other Fans 16% 22% Pumps

3 Energy Consumption by Pump Type Positive Displacement 27% Rotodynamic 73%

4 Typical Centrifugal Pump Performance Curve Function of pump design, and rotating speed

5 System Curve Function of site conditions: Hydraulic lift, piping

6 Pump Operating Point Adding comfort margins to the calculated system curve to ensure a sufficiently large pump will generally result in installing an oversized pump, which will operate at an excessive flow rate or in a throttled condition, which increases energy usage and reduces pump life.

7 Performance curves at various pump speeds

8 Benefits of variable speed pumping Finite control of flow as conditions vary Pump mechanical wear reduced (bowl, impeller) Bearing life increased Seal life increased Reduced noise Reduced vibration Omit throttling valve (or reduce wear) Eliminate water hammer Reduced cycling on/off Reduced energy consumption

9 Percent horsepower Pump Affinity Laws 100% 90% 80% Pump load HP a RPM 3 Pump brake horsepower varies approximately as the cube of speed. 70% 60% 50% 40% Normally speed reduction limited to 70% or higher 30% 20% 10% 0% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percent Speed

10 Variable Speed eddy current drive vs. Throttled Discharge

11 Example No. 1 Proposed Project Payback Spreadsheet Client: Sabine River Authority Nominal Rating 700 hp 889 rpm induction motor Assumed bhp at full speed: 650 horsepower Assumed power cost: 0.08 $/kw-hr Assumed project cost: $190, % Speed Pump rpm Load hp Load kw kw-hr/yr Annual Cost Annual Savings Payback (yr) ,528, $282, $57, ,308, $264, $75,

12 Example No. 2 Proposed Project Payback Spreadsheet Client: Miami-Dade County Nominal Rating 2000 hp 600 rpm synchronous motor Assumed bhp at full speed: 1900 horsepower Assumed power cost: 0.08 $/kw-hr Assumed project cost: $250, % Speed Pump rpm Load hp Load kw kw-hr/yr Annual Cost Annual Savings Payback (yr) ,900 1,417 12,416, $993, ,629 1,215 10,645, $851, $141, ,385 1,033 9,051, $724, $269,

13 Available Motor Speeds AC Squirrel Cage Induction Motors Synchronous Speed = (120 x 60)/ no. of poles (pairs only) 2 Pole 3600 rpm 4 Pole 1800 rpm 6 Pole 1200 rpm 8 Pole 900 rpm 10 Pole 720 rpm 12 Pole 600 rpm 14 Pole 514 rpm minus about 1% slip

14 Variable Speed Options Variable frequency AC drives Eddy Current Drives Two-speed AC induction motors Wound Rotor AC Induction motors Fluid Couplings Rare earth permanent magnet drives Variable Pitch Sheaves

15 Variable Frequency AC Drives Fractional to Unlimited Horsepower Low and Medium Voltage Since 1970s Wide variety of configurations Improved over the years, but still occasionally problematic Converts AC line power to DC, and then reconstructs power to simulate sinusoidal AC power at adjustable frequency and voltage Probably the most common solution

16 Eddy Current Drives Fractional to 10,000 hp Suitable for low and medium voltage motors Since 1930s Horizontal, Vertical designs Air cooled, water cooled available Long-lived, very reliable Simple to diagnose and repair No conversion of electrical power Transmits adjustable torque from a constant speed AC motor

17

18 Two Speed Induction Motor Relatively Inexpensive Two connections required (essentially two starters) Limited to specific speeds and combinations Adjacent pole combinations can be very practical 2 Pole 3600 rpm 4 Pole 1800 rpm 6 Pole 1200 rpm 8 Pole 900 rpm 10 Pole 720 rpm 12 Pole 600 rpm 14 Pole 514 rpm

19 Wound Rotor Induction Motor Available to thousands of HP Available for low and medium voltage Common in 1950s to 1970s Generally expensive motor and control Special starting requirements Requires controlled resistance in rotor circuit, via slip rings and brushes Liquid Rheostat Step Resistor Banks Slip Power Recovery System (electronic frequency and voltage conversion)

20 Wound Rotor Induction Motor

21 Fluid Drives Available 100 to several thousand horsepower Hydrostatic unit interposed between motor and load Driven at constant speed by AC induction motor Slip loss characteristic proportional to percent speed Long lasting Can be high maintenance (oil leakage, oil contamination)

22 Rare Earth Magnet Technology Rare Earth Magnet ASD Introduced in 1999 Common trade name is MagnaDrive Received recognition as a competitor to Variable Frequency Drives due to reduced energy consumption Transfers torque across the air gap using magnetic force

23 Variable Pitch Belt Drive More adjustable than variable Limited to relatively small horsepower Often manually adjustable only Commonly called Reeves Drive

24 Thank you!