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Unlocking Efficiency: The Power of Variable Speed Drives in Your HVAC System

April 12, 2023

A Variable Speed Drive (VSD) is a device used to vary the speed, or RPMs of an electric motor. The most common motor in use today is the AC induction motor. The induction motor converts incoming power into rotating magnetic fields to turn a motor shaft. This shaft is connected to a driven load either directly or via belts and pulleys or a reducing gearbox. In the HVAC world, the driven load is often a fan or a pump.

Modern HVAC systems use Variable Speed Drives to control the flow of air and liquids in a system sized for the hottest (or coldest) day of the year. Rather than utilizing complex mechanical methods to throttle air or water in off-peak times, a Variable Speed drive allows you to simply slow down the electric motor driving the fan or pump. This creates a more controllable and reliable HVAC system resulting in a comfortable and happy customer, and the system operates at its peak performance point.

In HVAC applications, fans and pumps are mostly variable torque loads. This means the power required to turn the fan or pump decreases dramatically when slowed down. This phenomenon is described by the Affinity Laws for fans and pumps. For example, a fan running at half-speed (30Hz), may require as little as 15-20% of the power required to run at full speed (60Hz). This gives the building owner a tremendous opportunity for savings over the 13-15 year lifespan of the VSD.

There are additional advantages to using Variable Speed Drives. For example, ramping a motor up and down reduces maintenance costs and improves reliability by lowering inrush currents, providing longer belt life, and reducing hydraulic shock. In addition, many Variable Speed Drives can communicate with Building Automation Systems, interlock with safety devices such as High Static switches, and control flow via integrated PID logic even with multiple pumps.

ABB's wide portfolio of low and medium voltage AC drives are the key to helping you reduce your energy use, maintenance costs, and CO2 emissions.

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Perry Conte

Perry Conte

Perry is the Senior AC Drive Specialist at Hoffman & Hoffman.

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