Over the past few years, pool professionals have learned that “going green” can significantly lower a pool’s operating costs. Pumps and filters are among the items most scrutinized due to the vast amount of energy they consume. To reduce costs associated with water circulation and filtration, it is important to understand why pumps and filters consume large amounts of energy and what options are available to lower consumption — factors that also extend the motor life of the pump. This article will provide a few easy-to-follow steps to help pool professionals determine the best way to extend the life of their pump motors and reduce operational costs using variable frequency drives.
Variable Frequency Drives
Variable frequency drives (VFD) offer a significant return on investment, especially in semi-commercial or commercial aquatic operations (such as homeowner associations, apartment complexes, etc). They allow the pump to run at its most efficient point on the curve and lower maintenance costs by protecting the motor, allowing soft starts and decreasing water hammer, which protects the shaft and impeller.
The VFD acts to clean up the power going to the pump, thus giving good solid current to the motor, which helps to lengthen its life. It also offers better control of the pump itself and allows the pump to run at the exact optimum flow rate, as opposed to the use of butterfly valves to bring the pump within the given parameter. The VFD also houses the motor starter which, without the use of the VFD, would have to be purchased separately at a cost of $500 to $750. One last key benefit is the ramp-up start; this makes life easier on the motor and also eliminates the potential for water hammer and its destructive effects on plumbing systems.
Just by installing a VFD, you can save as much as 5 to 10 percent in energy costs by simply dialing in the pump flow where it actually needs to be and by regulating the power being sent to the motor. In summary, you can expect the following benefits:
- A “right-sized” pump providing the exact flow required
- Energy savings due to constant flow as filters get dirty (with optional flow sensor)
- “Off-hour” flow management capability
- Up to 98 percent efficiency — adjusts drive input voltage for best efficiency point
- Elimination of the need for a motor starter
- 2-step ramps (soft start feature)
- Overload trip protection for motor and drive from voltage spikes and phase unbalance
- Overall savings of up to 60 percent or more on pump’s electricity usage
In order to quantitatively work on reducing the operating costs associated with running a pump room, you must start by determining exactly what it costs to run your system. In order to determine this figure, you must first determine the GPM and TDH of the pump, how long each day the pump runs and the cost per kilowatt-hour your power company is charging. Once you have a clear dollar figure to tackle, you will be able to easily determine the payback of adding a variable frequency drive.
Step 1: Choose a VFD
Choosing a VFD is very easy. All you need to know is the phase going to the pump (single or three), the horsepower of the pump onto which you are installing the VFD and whether the drive will be installed indoors and outdoors. You 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 they are class B, for example, the drive can still be used but additional software may needed depending on the incoming voltage.
Step 2: Install the VFD
As long as you know wiring and power, most pool professionals can easily install the VFD. It’s simply wired in between the electrical power source and the pump motor. One thing to always remember is that VFDs require the use of a three-phase motor. So if you have single-phase power coming to the drive, the VFD acts as a phase converter and delivers three-phase power to a three-phase motor.
Step 3: Ensure correct pump selection
Proper pump selection (sizing) and optimal flow rates are additional ways to increase energy savings. Pump size is especially important as many pool pumps are oversized by design and thus 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 steps:
a. Determine flow rate in gallons per minute [GPM]. b. Calculate TDH, or total dynamic head (the pressure head difference between the inlet and outlet of the pump) to account for friction loss. Adding 20 feet of head for a dirty filter is optional. c. Refer to the pump’s performance curve to select the preferred unit. d. Locate pump horsepower required by plotting GPM vs. TDH (if plotted point falls between two pump sizes, select the next larger pump size). e. Do not oversize the pump. If the preferred pump does not provide a proper fit, consider a different pump model. f. Verify that the selected filter can handle the system’s flow rate and be sure the minimum backwash flow rates can be achieved.
Given the simplicity of installation, adding a VFD to an equipment room is a straightforward upgrade. And with significant cost savings in energy usage, maintenance and replacement costs, the VFD is a worthy consideration for the pool owner or service manager looking to lower the operating budget.
Comments or thoughts on this article? Please e-mail [email protected].
10 Steps To Help Reduce Energy Consumption/Pump Room Operating Costs
1. Replace pool pump with an energy-efficient unit.
2. Consider a variable speed pump (VSP). VSPs with permanent magnet motors and digital controls can save up to 90 percent in utility costs compared to one- or two-speed pumps with induction motors.
3. If using an energy-efficient one- or two-speed pump, make sure it is sized to the pool’s requirements.
4. Reduce run time or speed to lower energy use.
5. If using a one-speed pump, reduce filtration run time. In general, water needs to be circulated through the filter once every six hours for most commercial applications.
6. If using a two-speed or VSP, use the lowest speed to appropriately circulate the water. Reducing speed saves more energy than reducing run time.
7. If appropriate, install a variable speed drive (VSD) to run pumps efficiently.
8. Run the pool’s filtration system during off-peak hours when electricity demand is lower (generally between 8 p.m. and 10 a.m.). Install a timer or control system to automate hours of operation.
9. Keep intake grates clear of debris. Clogged drains require the pump to work harder.
10. To obtain maximum filtration and energy efficiency, backwash or clean the filter regularly, as required.
