Applications for Variable Frequency Drives
Variable Frequency Drive (VFD) installations can increase energy efficiency (in some cases energy savings can exceed 50%), improve power factor and process precision, and provide other performance benefits such as soft starting and over-speed capability. They also can eliminate the need for expensive and energy-wasting throttling mechanisms such as control valves and outlet dampers.
HVAC Supply Fan Motors
In the past, the flow in most variable-flow air moving systems were controlled by a damper at the inlet of the fan scroll or in some cases by a variable-pitch drive sheave. For most of these applications a VSD is much more efficient and retrofit is very cost-effective. For buildings that have a centrally controlled HVAC system, one VSD can be installed to achieve maximum kW savings.
Liquid Pump Motors
A variable speed drive can often provide smoother
operation compared to an alternative fixed speed mode of operation.
For example, in a sewage lift station, sewage usually flows through sewer pipes under the force of gravity to a wet well location.
From there it is pumped up to a treatment process. When fixed speed pumps are used, the pumps are set to start when the level of the liquid in the wet well reaches some high point and stop when the level has been reduced to a low point.
Cycling the pumps on and off results in frequent high surges of electric current to start the motors resulting in electromagnetic and thermal stresses in the motors and power control equipment, the pumps and pipes are subjected to mechanical and hydraulic stresses, and the sewage treatment process is forced to accommodate surges in the flow of sewage through the process.
When adjustable speed drives are used, the pumps operate continuously at a speed that increases as the wet well level increases. This matches the outflow to the average inflow and provides a much smoother operation of the process.