VARIABLE FREQUENCY DRIVES: SAVINGS FORMULAS

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VARIABLE FREQUENCY DRIVESSAVINGS FORMULAS
CALCULATIONS

• PRESENTED BY
• Richard R. Vaillencourt, PE
• LIME ENERGY CONSULTING TECHNICAL SERVICES
• 16810 Kenton Drive
• Huntersville, NC 28078
• 704-892-4442

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VARIABLE FREQUENCY DRIVES

• Why VFD not VSD
• TODAYS GOALS ARE
• Go over Pump/System curve basics
• Discuss the Affinity Laws
• Present a formula that accurately applies all the
  Affinity Laws
• Give you some ideas of what to look for
• Go over the calculations with examples
• Some practical application discussions

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PUMPS FANS

• System Curve All Friction

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PUMPS FANS
All Friction System
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PUMPS FANS

• System Curve Friction Static

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PUMPS FANS
Friction Static System
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PUMPS FANS

• Pump/Fan Curve

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PUMPS FANS

• Pump/Fan Curve System Curve

System Curve
Operating Point
Pump Curve
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PUMPS FANS

• Pump Curve

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Pump and System Formulas
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Pump and System Formulas
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Pump and System Formulas
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Pump and System Formulas
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Affinity Laws
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AFFINITY LAWS VFDs

• Apply only to CENTRIFUGAL devices
• Centrifugal devices are VARIABLE TORQUE devices
• VFDs also vary the voltage
• To maintain a constant VOLTS/HERTZ ratio

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Affinity Laws
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Affinity Laws
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Affinity Laws
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AFFINITY LAWS VFDs

• Many engineers recognize the fact that the
  affinity laws are for theoretical ideal
  situations in order to correct for this
  shortcoming in dealing with a real situation,
  every engineer brings his own adjustment factor
  to modify the affinity laws. The above cubic
  exponent is modified and substituted by an
  exponent 2.x, where 0 lt x lt 9, to be conservative
  in their energy calculation estimates. There is
  no consensus on a fixed value of 2.x, as 2.x is
  characterized by each engineer as based on
  experience. This characterization leaves plenty
  of room for interpretation, as the amount of
  experience of each engineer is different.
• Tumin Chan Engineered Systems August 2004

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Affinity Laws
System Curve
Operating Point
35 Ft
Pump Curve
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Affinity Laws
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Affinity Law Applications
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Affinity Law Applications
FIXED PART
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Affinity Law Applications
VARIABLE PART
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Affinity Law Applications
1st LAW
FIXED PART
VARIABLE PART
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Affinity Law Applications
3RD LAW
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PUMPS FANS

• CIRCULATE OR TRANSFER
• STATIC PRESSURE
• FRICTION LOSSES
• TOTAL PRESSURE

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PUMPS FANS

• DAMPERS VALVES
• THROTTLING
• OVERSIZED EQUIPMENT

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PUMP RETROFIT MEASURES

• Centrifugal pumps
• Throttling valves
• Multiple valves from a header
• Circulating loop pumps

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Pump and System Schematics
Is Hydraulically Equivalent To
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OPEN
SHUT
Valve 90 Closed Typical for (3)
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TRIPLE-DUTY VALVE 50 CLOSED
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TRIPLE DUTY VALVE 55 OPEN
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PUMPS FANS

• Triple-Duty Valve Curve

Ft of Head
GPM
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FAN RETROFIT MEASURES

• Centrifugal fans
• VAV
• Throttling dampers
• Recirculate to fan inlet
• VIV air control
• VFD fan speed control
• Exhaust fan control

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AIR HANDLING UNITS

• Variable Air Volume

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VFD EXAMPLE 1
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VFD EXAMPLE 1
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VFD EXAMPLE 1
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VFD EXAMPLE 1
What Speed Ratio Will Deliver 50 Flow?
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VFD EXAMPLE 1
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VFD EXAMPLE 2
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VFD EXAMPLE 2
Hmin 15 10 25 Ft
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VFD EXAMPLE 2
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VFD EXAMPLE 2
What Speed Ratio Will Deliver 50 Flow?
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VFD EXAMPLE 2
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PUMPS IN PARALLEL
100 GPM
Pump 2
100 Ft
150 GPM
25 Ft
50 GPM
Pump 1
VFD
EACH PUMP 100 GPM _at_ 100 Ft
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SENSOR LOCATION
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SENSOR LOCATION