When it comes to energy efficiency, one of the best things to have happened to HVAC equipment over the last couple of decades is the variable frequency drive. VFDs are now quite common on pump and fan motors in HVAC equipment. They account for energy savings of 35-50 percent over conventional constant speed equipment, and can result in a significant return on investment.
With energy efficiency not likely to go away as a factor in the HVAC marketplace, business managers and owners who employ personnel who install, troubleshoot, or repair HVAC equipment will need to ensure their employees are up to speed on VFDs.
If you aren’t convinced that HVAC equipment with VFD capacity is a good investment, here are a few things to know.
As you’re aware, VFDs can be set to specific speeds, allowing a motor to obtain multiple speeds. The motor speeds can be precisely adjusted, with controls allowing variations in the speed of the fan.
Conventional building HVAC applications are generally designed to operate pumps and fans at a constant speed. Mechanical means can be employed to reduce air or water flow to adjust to a variable building load, but the drive motor maintains full speed. Energy savings are negligible with mechanical adjustments, regardless of the cooling or heating load, as the drive motor uses nearly the same amount of energy. Mechanical throttling is simply not efficient. VFDs are an effective alternative.
In general, HVAC systems are sized to meet peak load conditions, which occur less than 5 percent of annual operating hours. So with a conventional system, the pump and fan motors use more energy than necessary at least 95 percent of operating hours. In addition, most systems are oversized to meet demand for underestimated, unexpected, or future loads.
VFDs help match system capacity to the load, and over the annual operating year, can generate significant energy savings. What’s more, there is less wear and tear on motors due to the slow starting speeds of VFDs. Induction motors draw a higher current when started than when operating at normal speed. Heat and stress are generated in the motor’s components; frequent starts and stops result in early motor failure. Further, a sharp current spike during start-up can overload circuits.
Another benefit of VFDs is that they generate less operational noise. As output frequency of drives decreases when responding to the load, vibrations generate noise that is transmitted through motor mounts to the workspace. Because VFD drives operate at higher frequencies, the noise is above the audible range.
Furthermore, VFDs in HVAC units are increasingly required to be in compliance with code.
The benefits of VFD technology are many, but the equipment is complex, and to realize energy savings, personnel should be well trained.
VFD training is recommended for those whose responsibility is to work on chilled water systems, waste water systems, in manufacturing, or in facility maintenance. Training is usually recommended for individuals with these job titles:
Realizing energy savings potential should be the focus of any VFD training. Students should learn to calculate energy savings using data derived from live measurements, and be able to plot data to show energy savings that VFDs offer over HVAC speed control designs.
Trainees should learn proper design recommendations so they can ensure installation and repairs involving VFD equipment will result in efficient, safe operation.
Trainings should include a classroom lecture to familiarize students with the basics of VFD, but also a hands-on lab portion, using a scopemeter. The scopemeter will help the trainee understand how improper designs lead to deterioration of the motor and other issues. Trainees should learn to program and troubleshoot upgraded equipment, how to manipulate external drive control wiring, and how to use troubleshooting skills for deciphering fault diagnostics and correcting problems.
Possible topics for a training include some of these:
NTT Training‘s three-day seminar on Electrical Maintenance: Variable Frequency Drives could be the preparation your employees need to learn installation, troubleshooting, and repair of variable frequency drive equipment. Good training will help your HVAC personnel ensure that the VFD equipment they work on will run efficiently and safely.
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