basics of vfd
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Siemens Building Technologies Building Technologies
Variable Frequency DrivesVFD Basics
Siemens Building Technologies Building Technologies
What is a VFD?
A Variable Frequency Drive is like the throttle on a car -• It adjusts the speed of an HVAC fan or pump motor, based on
demand, to save energy and prolong motor and mechanical component life
• Without a VFD, an HVAC fan or pump motor is either 100% ‘on’ or 100% ‘off’
• A VFD eliminates the initial power surge and mechanical shock of switching the motor from ‘off’ to 100% ‘on’
• A VFD conserves energy when an HVAC control systems senses that a fan or pump motor can meet heating or cooling needs by running at less than 100% power
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Electric Motor Facts
• Electric motors account for more than two-thirds of all energy used in industry
• 63% of the energy consumed is linked to air & liquid flow • A typical 50HP industrial motor, with an efficiency of 90%,
costs over $25,000 to operate continuously over a year.
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Other17%
Ventilation& Cooling
52% Lighting31%
Energy Usage in Office Buildings
• More than half the energy consumed by AC motors powers air conditioning equipment.
• Electrical energy costs are often the largest expenditure for building owners.
• Reducing energy demand and improving the working environment of a building are main objectives of facility managers.
• The principle reason for using VFDs is to reduce energy costs.
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Why Use VFDs for HVAC Applications?
Improved• Energy savings• Simplified motor control panel design• Temperature regulation & comfort• Monitoring
Reduction in• Mechanical component stress• Damper commissioning • Cabling• Main power supply capacity• Peak demand• System components • Noise
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Energy Savings Comparison
Potential energy savings using a VFD vs. modulating flow with a damper
Flow Rate (%)
Inpu
t Pow
er (%
)
10
10 20 30 40 50 60 70 80 90 100
20
30
40
50
60
70
80
90
100
110
120
130
140
Damper
SED2 VFD
Ideal Fan ControlEnergy Saving
Potential
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How Does A VFD Work?
• It changes the speed of an AC HVAC fan or pump motor by adjusting or varying the frequency and voltage. For comparison, a DC motor speed is adjusted by only varying voltage.
• Typical frequency adjustment range in HVAC applications is from 10 - 60Hz AC. A VFD is wired in series between main power and motor.
• A Bypass is added to “Bypass” the VFD and run on main line power so HVAC operation is not interrupted if the VFD needs servicing
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How Does A VFD Vary the Frequency?
Switches (IGBT’s)
VFD Block Diagram VFD Block Diagram
Motor
Main Power
Rectifier Capacitor Motor
• A VFD, AC inverter, or electronic speed controller for AC motors converts the AC supply to DC using a rectifier (diode), then converts it back to a variable frequency by using a inverter bridge.
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VFD Specifying
Standard Features vs. The Options Game• When specifying VFDs –• Don’t play the "Options Game" – make sure you get the most
standard features for your money! • Make sure VFD installers are certified
by the manufacturer to get the most out of the drives capabilities.
• Make sure the drives are specified with advanced features, such as an integral harmonics reduction capability.
• Get more. Specify Siemens.
Siemens Building Technologies Building Technologies
• Low harmonics design• Small enclosure size• Many standard
features• Reduces operating
cost• Low power losses/high
efficiency• Minimal effect on
customer power• Wide power range –
from ½ to 125 HP
Siemens SED2 VFD Advantages