The energy saving advantages of VFDs for HVAC applications

Posted on 29th Nov 2022

As we deal with climate change, energy conservation is a primary importance for all governments worldwide. The technology used in heating, ventilation, and air conditioning (HVAC) also plays a key role in energy utilization.

The majority of buildings, including offices, retail stores, manufacturing facilities, and schools, have HVAC systems, which are responsible for about 40% of a commercial building's total energy costs.

These systems are quickly becoming more energy-efficient, which reduces carbon emissions and energy expenses.  However, variable frequency drive (VFDs) can be an excellent choice if you want to save a lot of energy.

Learn more about VFDs in this article by Darwin Motion, including how they can reduce energy consumption in applications involving HVAC systems.

How do VFDs contribute to energy conservation?

Centrifugal fans and pumps connected to 3-phase motors that are operating at full-rated speed and only under the control of a direct-on-line (DOL) or star-delta (Y/D) starter are all too common in the building services industry.

Under these circumstances, electrical power consumption can be thought of as being proportional to the cube of the motor shaft's speed, meaning that it will always be at its highest point or very close to it.

The real air flow or liquid demand from the process is not taken into consideration, and flow is typically managed by inefficiently throttling the ducting or pipes with dampers or valves.

By lowering the speed of the motors that power these fans and pumps and operating them in accordance with process demand, installing a Darwin Motion VFD – MATRIX 680 provides the ability to electronically reduce flow and save a considerable amount of energy.

Less wear and tear is experienced by belts, pulleys, and bearings since the HVAC plant is not always operating at maximum speed.

As a result, there are less maintenance needs and longer component lifespans. Even more effectively than merely slowing down the fan and pump motors and leaving them running at a lower speed is flow control.

Even more energy and money savings are produced when VFD usage is expanded throughout the HVAC plant, along with additional feedback systems.

Instead of just slowing down the fan, a VFD can change the speed in accordance with the real operating conditions by, for instance, actively monitoring duct pressure using a pressure sensor.  

By using a closed loop feedback signal from such a sensor, the majority of modern digital VFDs can implement simple PID control. As pressure approaches the desired target (set point), the VFD automatically reduces the motor speed and the fan slows down. If this is not necessary, the VFD can enter "sleep" mode and turn off the fan while it waits for a change in system demand, which saves energy.

When demand rises and pressure begins to fall, the inverter speeds up the motor, which raises duct pressure. Reduced wear and the benefits that follow result from not running the pumps and fans at full speed.

Utilizing VFD to control several motors reduces complexity and costs

Depending on how the HVAC system is built, more than one motor may be controlled by a single VSD.

As mentioned earlier, several fan and pump motors are managed by a single VFD and run at the appropriate speeds for the circumstances rather than at full capacity, which lowers energy usage.

Not all HVAC systems are suited to this method. If employed, each motor should have its own overload protection and monitoring system. The current drawn by individual motors cannot be detected by VFD; it can only measure overall current.

There are extra advantages if this strategy is successful. For instance, fewer VFD require less room. Less overall system control is necessary, which results in less complexity.

Smart HVAC systems with VFD

An intelligent HVAC system that is network monitored and controlled and operates the heating and cooling at peak efficiency only when necessary is the best answer for energy efficiency.

The building manager can further reduce energy costs by closely monitoring and analysing the performance of the HVAC system.

The data can be used to pinpoint HVAC issues and enhance efficiency.

How can you choose the best VFD to lower your energy usage?

In a variety of industries, Darwin Motion assists electrical contractors and end users in choosing the optimum VFD for their HVAC pumps and fans. For free guidance and suggestions, get in touch with our team of professionals right away.