Step 1: Choosing a VFD
Choosing a VFD is simple. All one needs to know is the electrical phase going to the pump (i.e. single- or three-phase), the horsepower (hp) of the pump onto which the VFD is being installed, the voltage going from the power source to the drive, and whether it is being installed indoors or outdoors. An aquatic facility will see the greatest potential for savings when using a VFD with Class F motor insulation—be sure to check this on existing motors. If the motor is rated a class B, for example, the VFD can still be used, but additional software may need to be added depending on the incoming voltage.
Step 2: Installing a VFD
Basic knowledge of wiring and power is necessary to install a VFD. However, if unsure, an electrician should be hired to complete the installation. The incoming powerline from the electrical source should be connected to the incoming side of the VFD. Then, the pump motor is wired to the outgoing connection of the VFD. It is important to remember, VFDs require the use of a three-phase motor; therefore, if single-phase power is going to the VFD it will act as a phase converter, thus allowing it to be wired to a three-phase motor.
Step 3: Ensure correct pump selection
Proper pump selection (i.e. sizing) and optimal flowrates are additional ways an aquatic facility can increase energy savings. That said, the size of every pump should be checked as many tend to be oversized by design, which means they are bigger than they need to be. This happens because many architects and engineers look at what is required, then pick the next size up to be sure the pump can handle the job.
Pump selection tips
- Determine flowrate in lpm (gpm);
- Calculate TDH to account for friction loss (adding 6.1 m [20 ft]/head to account for a dirty filter is optional);
- Refer to the pump’s performance curve to select the preferred unit;
- Determine the required pump horsepower (hp) by plotting the litres per minute (gallons per minute) versus TDH (if the plotted point falls between two pump sizes, the next larger pump size should be selected);
- Do not oversize the pump—if the preferred pump does not provide a proper fit, consider a different model; and
- Verify the selected filter can handle the system’s flowrate, and be sure the minimum backwash flowrates can be achieved.
Long-term benefits
The greatest long-term benefit of installing a VFD is that it helps to extend the life of the pump motor, thus significantly decreasing maintenance and replacement issues. Further, pump motors last longer not only because of the VFD-enabled ‘soft start,’ two-step ramp up feature, but also because of the overload trip protection it offers, which protects the motor and drive from voltage spikes and electrical phase unbalance.
Mike Fowler is the commercial marketing/sales manager for Pentair Commercial Aquatics in Sanford, N.C. He has been with Pentair since 1992, starting his career in the technical services department at Purex Pool Products. Fowler has held many managerial roles within the company, including marketing, account management, and product management. He can be reached via e-mail at mike.fowler@pentair.com.
