VFDs

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VFDs

• Overview and
• Applications
• James K. Rogers, PE, CEM
• Motor System Management Workshop
• August 19, 2004

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VFD Agenda

• What are VFDs and how do they work?
• Other types of speed control
• Fans and blower applications
• Pumping system applications
• Process and other VFD applications
• Smart motor controllers
• Problems and precautions with VFDs
• Other VFD application tools
• Utility rebates

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The Best Motor Efficiency Opportunities

• Replace with Premium Efficiency Motor
• Replace with better sized (usually smaller) motor
• Install a VSD, especially if the load varies and
  the output must be throttled back or bypassed.

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VSD or VFD or What?

• VSD Variable Speed Drive
• ASD Adjustable Speed Drive
• VFD Variable Frequency Drive
• AFD Adjustable Frequency Drive
• VFD is sometimes called Inverter Drive
• A VFD is a VSD but a VSD may not be a VFD

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Some drives are big, but---
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VFDs are Not Just For Large Motors
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VFDs are getting smaller
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VFD Benefits

• Reduced energy usage Motor and equipment are
  speed controlled to provide the optimum flow
• Improved power factor Phase power factor can be
  improved to closer to 1.0
• Limited over-speed capability (depending on VFD
  sizing)
• Slower speed and built in soft start reduces
  mechanical stresses
• Motor usually runs cooler

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Other VFD Capabilities

• Phase change - Convert from single phase to three
  phase power.
• Frequency change - i.e. convert from
• 60 Hz to 50 Hz (without a motor generator)

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VFD Energy Savings - Automobile Example

• Controlling loads on constant speed fans and
  pumps by throttling back or bypassing is like
  driving a car by putting the accelerator to the
  floor and using the brake to control the speed.

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• Its not the motor speed reduction that saves
  the energy its the load reduction of the
  equipment being powered (fan, pump, etc.)

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Other Types of Speed Control

• Two speed motors
• Multi-speed gears
• Variable sheaves
• Magnetic coupling ASD
• ECM Motors with controls
• Variable speed PSC motor controls

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The MagnaDrive ASD
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Motor with Magnetic Coupling
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Pump Retrofit with Variable Speed Coupling
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MagnaDrive vs.. VFD
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Variable Speed ECM Motors
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Typical ECM Motor Savings(Nailor VAV Boxes)
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Variable Speed Controls for PSC Motors
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How can you tell if a VFDwill save energy (and
)?

• A constant speed AC motor driving a constant
  speed device (i.e. fan or pump)
• A variable load --- moving air, water, etc
• A large percentage of time at less than full load
• Presently controlled by one of the following
• Inlet throttling
• Outlet throttling
• By pass loop
• No control

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Potential HVAC VFD Applications

• Supply fans
• Return fans
• Exhaust fans
• Cooling tower fans
• Chilled water pumps
• Condenser water pumps
• Heating water pumps
• DHW Pumps
• Chillers

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Four VFDs for One AHU
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Federated Stores AHU Savings from VFDs
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Cooling Tower Fans are Good VFD Candidates
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Chiller VFD Paybacks
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Pumping VFD Applications

• Chilled water
• primary
• secondary
• tertiary
• Condenser water
• Hot water - heating coils
• Hot water - domestic
• Swimming pools
• Irrigation systems
• Fire and cooling water loops

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Shipboard VFD Opportunities
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Seawater Pump
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150 HP Shipboard Fire Pump
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Hydraulic Pumps for Rudder
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Rudder Hydraulic System
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Rudder Piston
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Other Facility Applications of VFDs

• Swimming pool pumps
• Irrigation pumps
• Elevators?
• Escalators ?
• Moving walkways?

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Process Applications of VFDs

• Usually involve fans or pumps
• Controls are often the key to savings
• Examples
• Injection molding machines
• Hydraulic powered machinery
• Glass cooling fans
• Air filters
• Liquid filters
• Water and wastewater treatment

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Injection Molding Machines
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Molding Machine Savings
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Process Applications of VFDs

• Usually involve fans or pumps
• Controls are often the key to savings
• Examples
• Injection molding machines
• Hydraulic powered machinery
• Cooling fans (i.e. glass forming)
• Air filters
• Liquid filters
• Water and wastewater treatment

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Wastewater Facilities Have Many VFD Opportunities
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Water and Wastewater Facilities VFD Applications

• Plant water pumps
• Transfer pumps
• Lift station pumps
• Mechanical aeration
• Fine bubble aeration
• Incinerator combustion fans

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http//www.energy.ca.gov/process/pubs/vfds.pdf
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Mechanical AerationPump or Fan?
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VFDs on Mechanical Aerators at GLSD

• VFDs installed on eight 75 HP mechanical aerators
• Installed self cleaning dissolved oxygen (DO)
  sensors
• DO measurements go to Andover Controls EMS
• EMS adjusts aerator speed to maintain desired DO
• Benefits
• 20 energy savings - about 100,000 /yr..
• Reduced maintenance costs
• Improved treatment of wastewater

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Smart Motor Controllers

• Not a VFD (or VSD)
• Use when the load changes but speed must be
  constant
• Based on a NASA patent (Nola)
• Increases efficiency by improving power factor by
  adjusting voltage
• Requires long periods at low load for decent
  savings
• Includes soft start

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Smart Motor Controller Applications

• Escalators
• Moving sidewalks
• Conveyor systems
• Machine tools
• Lathes and milling machines
• Drilling tools
• Grinders and crushers
• Ripsaws
• Textile machines
• Motor-Generator Sets
• Slot machines (mechanical)

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Escalator Energy Savings
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VFD Cautions and Caveats

• Motor compatibility?
• Power quality concerns - esp. harmonics
• Distance between motor and drive
• Drive environment - clean and cool
• Separation of input and output power
• Backup - i.e.auto by-pass
• Resonant frequencies?
• Motor cooling at low speed
• Mechanical stress at over-speed

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An Example of VFD Power Conditioning
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Separate Power and Control Circuits
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VFD Application Tools

• VFD Manufacturers - Savings estimators
• EPA Tools - QuikFan
• DOE Tools
• MotorMaster
• PSAT
• ASD Master

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DOE Energy Tools
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Thank You

• Jim Rogers
• 978-256-1345
• jim.rogers_at_comcast.net