Variable Frequency Drives VFD Basics

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

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.

Energy Usage in modern office buildings 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. Other 17% Ventilation & Cooling 52% Lighting 31% Energy Usage in modern office buildings The main reason that contractors and building owners install AC inverter drives is to provide an efficient method of controlling the speed of the AC motors on the air conditioning machinery. Reducing the speed of the motor results in a reduction of the flow of air or cooling water and a corresponding reduction in the energy used. AC inverter drives are normally the most efficient means of controlling speed. This control method allows the air conditioning system to be constantly adapted to the demand on the building (number of people working, outside environmental conditions etc.) with the building owner benefiting by way of a lower electricity bill. There have been mechanical methods of adjusting flow rates available for many years. The AC inverter drive, however offers advantages in terms of efficiency and control which will be discussed in this presentation. In a modern building more than 50% of the energy used is consumed by the air conditioning system. The potential for savings is therefore very significant. In many countries government offers incentives to optimize the savings. Consequently new installations are invariably fitted with AC inverter drives.

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 Advantages for the : Consultant (offering better solutions to the client) Building Owner (Lower operating costs with higher comfort levels) Panel Builder (reduced labor costs due to simplified fewer components) Commissioning Engineering Contractor (reduced total time and flexibility to compensate for variations in other equipment) 1

Energy Savings Comparison Potential energy savings using a VFD vs. modulating flow with a damper 140 130 Damper 120 110 SED2 VFD 100 90 Ideal Fan Control 80 Input Power (%) 70 Energy Saving Potential 60 50 40 30 20 10 Flow Rate (%) 10 20 30 40 50 60 70 80 90 100

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

How Does A VFD Vary the Frequency? 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. VFD Block Diagram Motor Main Power Rectifier Capacitor Switches (IGBT’s) Motor

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 SED2 VFD Advantages 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