The installation process requires smarts, savvy, and attention to detail.
By William Wagner
Nothing beats country living. The air is pure, the spaces are wide open, and the stars shine brightly at night. But unfortunately, it isn’t all hunky-dory: There’s that nagging problem with water pressure.
“Living on a well (in the country), you have some unwritten rules,” says Terry Smith, product manager–new development, water systems drives, and protective devices for Franklin Electric in Fort Wayne, Indiana.
“Everybody knows you don’t flush the toilet or run the dishwasher while someone’s in the shower.”
Enter variable frequency drives (VFDs), which have changed everything in the past decade or so.
“They’ve helped us get away from pressure fluctuations and achieve constant pressure performance,” Smith says. “With constant water pressure, all your water-related appliances work better. If you’re living on a well and you go to a hotel somewhere in the city, you almost see a night-and-day difference just in the water flow in the shower if you don’t have a VFD system. Everybody can relate to that. It’s the easiest way to describe what the difference is.”
Another benefit of VFDs—at least where groundwater system professionals are concerned—is they basically troubleshoot themselves once they’ve been installed. However, the emphasis is on once they’ve been installed.
The installation process requires smarts, savvy, and attention to detail on the part of the contractors. Here are some of the variables to consider:
This, of course, is job No. 1 when installing a VFD. Given that VFDs store energy even when the power is off, it’s imperative to proceed with caution. Furthermore, don’t forget to consult the installation manual before you get started.
“These drives are different in that they’re chock-full of electronics with things like capacitors that store energy even when the power isn’t on,” says Tom Stephan, a training manager with Goulds Water Technology in Seneca Falls, New York. “Every installation manual will tell you what the wait time is when you have to get into, say, the output. The smaller units generally give five minutes, but it’s a longer wait time as the units grow in capacity. That’s important to consider. Some contractors aren’t used to waiting for the energy to dissipate.”
Blocking and Tackling
That’s how Stephan phrases it. He’s referring to the fundamentals that make the system run properly.
“It’s stuff like sizing and selection,” he says. “So first and foremost, make sure you’ve selected the proper drive.”
On that front, an important consideration is amperage.
“You have to make sure the drive can handle the amperage of the pump,” Stephan says. “Most drives are rated by horsepower, with the general idea being to get people in the right ballpark. But we always want to check the amperage ratings of the drive to make sure they can handle the amperage—you want to make sure everything is matched up.
“And in terms of single or three phase, there are different types of drives. There are drives that are specifically for single-phase input and drives that are three-phase input. We also have to know the amount of power that is coming in. If we have 230 voltage, we’ve got to have a 230 drive. Generally, if you apply a larger voltage than the rating, you’ll wind up buying a new drive [because it will get fried]. Voltage is one thing that needs to be consistent in terms of supply, drive, and motor.”
Let’s say you’re listening to the radio, and a weird hum overtakes your singing along with the tune. If a contractor hasn’t done his job right, the culprit might be your VFD.
“A VFD, by nature, is an active, electronic, high-energy switching device,” Smith says. “As a result, it creates a lot of higher-frequency electrical noise. Especially with residential or commercial applications, you can interfere with some adjacent electronics. In rural areas, AM radios, telephone systems, and LED lighting are popular. VFDs interact with those systems in different ways.”
So, what’s the remedy?
“First and foremost, you want to have a good earth-ground connection,” Smith says. “Most VFDs have advanced electrical filtering built in that helps to correct and reroute the noise, but a lot of times that filtering is only as good as the earth-ground connection. If the ground connection is good, it will shunt away that energy from other devices.”
Smith adds this is an instance where a contractor needs to pay close attention to the installation manual: “Make sure to follow your manufacturer’s routing recommendation. Most manufacturers will offer fairly in-depth wiring recommendations.”
Wiring isn’t just a key to filtering out noise—it’s one of the linchpins of the whole shebang. And if you want to get the wiring right, you need to keep paging through that manual.
“What you’ll find is that there’s an input chart and output chart [in the manual],” Stephan says. “I tell everybody not to guess—just use the wire-sizing chart.”
A number of things can happen if you wire the VFD wrong—and none are good. Among the most common results are error signals from your drive when it’s running.
Contractors who have never worked with a three-phase motor may not realize the importance of ensuring the rotation is correct.
“Every time we use a three-phase motor, we have to make sure the rotation is correct,” Stephan says. “On the submersible side, the key indicator of correct rotation is your maximum flow and head. On a surface motor, it’s easier because we can physically see the motor and rotation.”
One of the keys here is to be sure you’re using the correct type of pressure sensor, or pressure transducer. And that’s easier said than done because there are many types.
“The two main categories are the voltage transducer and milliamp transducer,” Stephan says. “In other words, one’s voltage and one’s current. You’ve got to make sure you’re using the right kind because they can look exactly the same. It’s fairly easy to mix them up unless you’re looking at a part number.”
The correct placement of the sensor is equally imperative.
“This can be the Achilles’ heel of the whole system,” Smith says. “You can only regulate pressure as well as you can measure it. And if the sensor is in an improper place, you’re at risk there. For example, you want to place the sensor in a straight run of plumbing. If you put it near, say, an elbow, where you’ll encounter turbulence, that can create localized pressure fluctuations.”
It falls upon the contractor to set the overload.
“The drive needs to have protection built in,” Stephan says. “It might be a dipswitch, a dial, or a keypad. Basically, what you’re doing is limiting the amount of current. If you set it too high, you’re allowing too much current. If you set it too low, you could get some nuisance tripping. That means you could get an error on your drive because of an incorrect overload setting.”
So, when it comes to installing variable frequency drives, keep in mind these seven tips, and as always—be smart, be savvy, and pay attention!
William Wagner is an award-wining writer, editor, and project manager for Wagner Communications. He has written for magazines, newspapers, books, and websites. He lives in the Chicago area and can be reached at firstname.lastname@example.org.