18 Mar Greenheck – VFDs versus Motor Starters for Fan Control: What is the best option for controlling fans?
In commercial building ventilation systems, the fan motor represents a significant part of the investment. To protect it and improve its performance, there are two common solutions: variable frequency drives (VFDs) and motor starters.
Both devices manage the flow of current to the motor and provide protection against overloads or short circuits. However, VFDs offer additional advantages that can translate into efficiency, energy savings, and greater control. In this article, we compare both systems to help you choose the most appropriate option for your application.
How do they work?
Motor Starter:
Allows the motor to be started and stopped in a safe and controlled manner. It uses a contactor to start or stop the power supply and a thermal relay that interrupts the circuit in the event of overcurrent or overheating, thus protecting the equipment.
Variable Frequency Drive (VFD):
Controls fan speed by adjusting the frequency of the electrical current. It operates digitally and allows precise modulation of airflow, better adapting to changing space conditions.
VFD: More than protection
Although the initial cost of a VFD can be up to three times higher than that of a motor starter, its medium- and long-term benefits make it a strategic investment:
Speed Modulation
VFDs allow fan speed to be adjusted based on demand. Most work with 0-10V modulation signals, compatible with BMS systems and HVAC controllers, optimizing temperature, humidity, and indoor air quality (IAQ).
Simplification Systems
Because variable frequency drives allow the same fan motor to operate at different speeds, they can make it possible to install a single fan for an application where two would have been required. For example, when a store is open, it may need a fan operating at 10,000 cfm. But when it’s closed, it only needs a fan operating at 2,000 cfm. With a VFD, it can be the same fan.
Reduced Maintenance
VFD soft start minimizes mechanical and electrical stress on the motor, extending its lifespan and reducing the need for repairs.
$ Operational Savings
By adapting energy consumption to actual demand, VFDs reduce monthly electricity bills.
Regulatory Compliance
The U.S. Department of Energy promotes the use of VFDs as an energy efficiency measure. They also help meet requirements such as the Fan Energy Index (FEI), mandated by 2030. A fan with a VFD can achieve a higher FEI by operating at lower speeds based on demand.
Case Studies
Parking Garages
A propeller fan may need to operate at 3,000 cfm regularly, but up to 10,000 cfm during high-traffic events. Should you install two fans or one with a dynamically adjustable VFD? A VFD is the most versatile and efficient option.
Warehouses
When the temperature is low, the fan can be off; if it exceeds 75°F, it should operate at 100%. A VFD allows you to operate at 50% or 80% as needed, maintaining thermal comfort without wasting energy.
🌬️ Ceiling Exhaust Fans
In cases where ventilation always requires the same flow rate and speed adjustment is not required, a basic motor starter may be sufficient.
Conclusion
The choice between a VFD and a motor starter depends on key factors such as the type of application, fan power, and efficiency and control goals. For small fans, a motor starter may be sufficient. But in more complex systems or with variable requirements, a VFD not only protects the motor but also improves its performance, reduces energy consumption, and ensures compliance with future regulations.
At PrimeLines, as representatives of Greenheck, we help you choose the most efficient and modern solution that meets the quality and sustainability standards of today’s HVAC market.
No Comments