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Variable frequency drives in extraction and ventilation systems
Variable frequency drives control the speed of electric motors by adjusting frequency and voltage. In extraction and ventilation systems, this technology is primarily used to adjust fan power and flow rate to actual demand. This is particularly useful in situations with varying operating conditions, multiple measurement points, or systems that do not require their maximum airflow capacity at all times.
Why Speed Control Can Save Energy
For fans, power consumption varies significantly with speed. If the required flow rate is adjusted by reducing the speed rather than by throttling, energy consumption can be significantly reduced. This requires proper design of the entire system and a suitable motor.
Key Selection Criteria
✔ Motor power and rated motor current
✔ Mains voltage and connection type
✔ Desired frequency and speed range
✔ Control and setpoint signals
✔ Protection class and installation situation
✔ Cable lengths and EMC requirements
Control Based on Process Requirements
A variable frequency drive can be operated manually via a setpoint or automatically via a control system. In extraction systems, control via pressure or flow sensors is particularly useful. If the system resistance changes, the speed can be adjusted automatically. This helps maintain the desired operating condition more stably.
Typical Functions
| Function | Meaning | Benefits |
|---|---|---|
| Speed Control | Adjust engine speed | demand-based flow rate |
| Ramp-up times | Smooth startup and shutdown | lower mechanical stress |
| Setpoint Input | Process external setpoint | Automation possible |
| Error output | Report Issues | Improved equipment monitoring |
The motor and drive must be compatible
It’s not just the rated power that matters. The rated current, motor type, cooling system, and intended speed range must also be taken into account. At very low speeds, a motor’s self-cooling capacity may decrease. In addition, additional filters or shielded cables are recommended for long motor cables, sensitive electronics, or special EMC requirements.
Typical Applications
✔ Centrifugal fans in extraction systems
✔ Centralized filter systems with varying air demand
✔ Systems with automatic pressure control
✔ Multiple workstations connected to a shared piping network
✔ Process air systems with variable operating conditions
FAQ
Can any motor be operated with a variable frequency drive?
Not automatically. Motor specifications and suitability for the intended speed range must be verified.
Does a variable frequency drive always save energy?
This is especially true when the flow rate is frequently required to be below the maximum capacity.
Can a pressure sensor control the variable frequency drive?
Yes, provided that the signal type and control concept are appropriately designed.
Why are EMC measures important?
Variable frequency drives generate rapid switching operations. Proper installation reduces interference with other electrical components.
Is a frequency converter also suitable for retrofits?
Often yes, provided that the motor, power supply, control system, and installation are suitable for this purpose.
Design Consulting
To make a selection, the following information is required in particular: motor power, rated current, line voltage, desired control range, and the planned control concept.
