Variable speed drive for HVAC applications

Paul Boughton

WEG has launched a  frequency inverter CFW501 that has been designed to meet the needs of the heating, ventilation and air conditioning (HVAC) industry.

The robust, compact and easy-to-use drives are currently available with a power range from 0.18 to 7.5kW and are suitable for applications in buildings, such as hospitals, schools and universities, for cooling  and heating systems in commercial buildings, as well as for all pump and fan applications in general. Thanks to their advanced features and design, they help users to optimise the operation of their motors, while being quick and easy to install and cost-effective to maintain.

The CFW501 is based on the same modular plug and play platform as the CFW500 product family. The units include a built-in micro-PLC, programmable according to IEC 61131-3, and an advanced intuitive HMI. The interface offers specific engineering units for HVAC applications, such as bar, mbar and m3/h, and is also available as a remotely controlled version for installation in a panel door. To allow for direct communication with the most important protocols in building automation, the CFW501 supports Bacnet, MetaSys N2 and Modbus-RTU.

Like the CFW500 drives, the new inverter is designed with simplicity of installation and operation in mind. It can identify up to 64 different plug-in modules, which makes it simple to also connect to major fieldbus systems including Profibus-DP, DeviceNet and CANopen.  Additionally, expansion plug-in modules are available enabling easy customisation for bespoke applications.

A fire mode function prevents the motor from stopping when critical operating conditions are detected by the drive, such as a high internal temperature. As most of the drive failures are inhibited in order to keep the motor running no matter what the conditions are, the CFW501 is suitable even for very demanding applications like smoke extraction fans and exhausters. Thanks to special conformal coating, its electronic boards are well protected against dust, moisture and chemicals.

The unit is equipped with a bypass function which enables the user to power the motor directly from the mains. Both, scalar (V/f) and vector control methods are available to control AC electric motors. The inverter features three PID controllers for enhanced process monitoring and more precision; the main PID controls the process while the two additional ones are intended to control independent process variables. Depending on the motor speed and load conditions, the power saving function reduces flux, thus decreasing losses and improving energy efficiency.

Other key features include the ability to identify load problems such as dry pumps and broken belts, a sleep mode that optimises motor usage and avoids very low speeds, protection against short cycles and the ability to monitor PTC thermal sensors. Part of the modular design is an easy-to-maintain-and-replace ventilation kit, and a filter maintenance alarm provides the user with a warning when it is time to clean or replace the air filter. Among the accessories is a flash memory that allows users to save up to two different drive settings and makes the data portable so it can easily be copied to multiple devices.

The current CFW501 range up to 7.5kW comes in three different frame sizes (A: 0.18 to 2.2kW, B: 1.1 to 4.0 kW, C: 5.5 and 7.5kW) and WEG plans to further expand the range to include a rated motor power of up to 22kW, which will be made available next year.  

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