SEEING THE DIFFERENCE

Here’s an example of the difference between a traditional pump and a VFD on a pool that had a required turnover rate of 267 gpm. Depending on the size of the motor, hours of operation and the cost of the VFD, the normal payback period is one to three years.

We can all agree the cost of electricity is not coming down. This is the basis for the “green initiative” that some facilities are embracing. After all, a number of products and technologies exist that can make facilities operate more efficiently and at a lower cost. What’s more, power companies are willing to help defray the cost of new equipment.

The main way I’ve been helping my customers realize the promise of green technology and lower energy costs is with variable-frequency drives or VFDs. VFDs are used on larger three-phase pump motors such as commercial pool filtration systems, waterfeature pumps, slide pumps and booster pumps for lazy rivers.

Until recently, most engineers who design filtration systems would specify a pump and motor that meets and/or exceeds the turnover rate needed for a maximum bather load situation or the specific requirement of the local health departments. The pump and motor were intentionally oversized to meet these requirements.  Therefore, it is not unusual to find a pool that has a turnover rate 30- to 40 percent greater than what is needed for normal pool operation.

Installing VFDs on these pump motors offers a number of benefits; however, the most compelling is the ability to control the speed of the motor to produce the needed water flow as opposed to “all the pump can do.” This reduction in flow produces a significant decrease in energy needed to run the motor. A 20 percent reduction in water flow will result in 50 percent decline in energy consumed.

For example, we recently found a pool that had a required turnover rate of 267 gpm, but a system that was moving 711 gpm with a 15hp motor. Using a VFD, we reduced the flow 44 percent to 400 gpm, produced an 81 percent reduction in energy consumption, and reduced electrical operating costs from $5,580 to $1,045 annually, without sacrificing water quality. Depending on the size of the motor, hours of operation and the cost of the VFD, the normal payback period is one to three years. However, to demonstrate the possibility of a real return on investment, it is important to install quality equipment with a good warranty that extends past the payback period.

In addition to energy savings, VFDs produce other valuable benefits. Three-phase motors will only start on three-phase power, but will continue to run on single-phase power should there be a loss of power on one of the three power legs. This event is called “single phasing,” and will burn up the three-phase motor in a matter of minutes. VFDs have the ability to convert the single-phase power back to three-phase to keep the motor running at reduced speed. If the power required to run the motor at the selected speed is more than the VFD can produce with the single-phase power, the VFD will shut down to protect the motor and itself. 

Another benefit of using a VFD is the ramp-up and ramp- down feature of starting and stopping a motor. Cutting motors off and on causes more wear and tear on motors than running them continuously. This is due to the spike in energy needed for the “hard start” of the motor. Hard starts require up to 700 percent of the energy needed to run the motor, plus the torque generated to overcome the back-pressure creates stress on the shaft and impeller. The ramp-up and ramp-down feature of the VFD eliminates these issues and extends the life of the pump motor and the impeller.

A VFD also can save on labor costs. Some units have timers that will allow the user to program start/stop times as well as various speed changes that may be desired during operating and nonoperating hours, eliminating the need for pool personnel to complete these tasks.

One of the other possible benefits of installing a VFD is the participation of the local utility company to provide a substantial rebate for the purchase of the VFD based on the actual energy savings that the unit achieves. Our local utility offers a rebate of $.10 per kilowatt hour saved for the first year, up to 50 percent of the unit and installation costs.

One of the questions that our prospects ask is “Why would the utility company pay me a rebate to use less of what they sell?” The reason is simple: It is cheaper for the utility company to pay a rebate to “reduce the use” than it is to build a new power plant. The ability of the utility company to continue to meet the expanding needs of future customers without having to build new power plants is a huge incentive for them to provide rebates for equipment that is proven to reduce power consumption. The utilization of VFDs on larger pool pump motors can save tens of thousands of kilowatt hours per year per motor. With a recent VFD installation on two 20hp pump motors for a continuous use on a lazy river, we were able to save more than  210,000 kilowatt hours per year.

This is the best win-win-win-win situation available to the aquatics industry today. The customer wins because of the significant reduction of energy costs; the environment wins because it takes fewer natural resources to generate the energy to operate the pool; utility companies win because of added availability of power to provide to an expanding market; and the equipment seller wins by making money on the sale of the equipment to the customer.