When it comes to improving the state of our nation’s infrastructure, pumps have an important role to play.
By Carol Brzozowski
Much is said about the deplorable condition of the United States’ aging infrastructure and its impact on water efficiency. While pipes may be first to come to mind, pumps also play a role in efficiency challenges.
Pipes garner more attention because pipe failures are big news, points out Bryan O’Toole, vice president sales (water utilities) for Grundfos. “You’ve got a big mess in the street,” he says. “You’ve got to close the street. You’ve got a sinkhole. You’ve got something you can show on the news. If your pumps catastrophically fail, you’re just not going to have water. While that might make the news, the visual of it is not as good.”
Douglas Potts, P.E., senior design engineer for American Water, points out that at a typical water utility, more than 90% of the electrical consumption is used for pumping water.
“Therefore, it is crucial that pumps and pumping systems be as efficient as possible,” he adds. “Our experience—as well as industry literature—shows the average pump/motor efficiency [wire-to-water efficiency] is in the range of 60 to 65%. New pumps and motors can achieve a wire-to-water efficiency of up to 85%.”
The loss in efficiency results in 30 to 40% higher electrical consumption as compared to a water utility operating new or like-new pumps, Potts adds.
“Pumps and motors must be routinely refurbished or replaced to maintain optimal efficiencies. Without proper maintenance, pump efficiencies will continue to decline,” he says.
Multiple needs are constantly competing for water utility dollars, Potts points out. When pumps appear to be operating properly, maintenance is often deferred.
O’Toole explains that one of the biggest challenges for water utilities is balancing the older systems.
“The one thing about water distribution, and the pumps associated with it, is that pumps last a long time because it’s a really clean application for a pump,” he says. “The water is generally really clean, nice, and cool. It’s one of the ideal applications for the centrifugal pump, so they last a long time.”
As a result, some systems may have inefficient pumps, he adds.
“Over the years, we’ve all gotten smarter in the pump business,” says O’Toole. “We don’t have to make our pumps as heavy, but we want them to be more efficient. We have safety factors in the designs.
“There are a lot of pumps right now that are very inefficient because of their nature, and they’ve been around for 20 or 30 years—in some cases, 40 years,” he says. “The challenge is what do you do with those pumps that are working fine and how do you optimize that efficiency in a pump that’s been running for 30 years and is designed with a mindset from 30 years ago when there wasn’t a concern about energy efficiency?”
|Photo: THOMPSON PUMP
There are several factors to be considered in
retrofitting and upgrading pump systems.
There also are cost concerns, O’Toole points out.
“You can take a perfectly good pump out and put in an optimized, efficient pump, but with money being the way it is right now, that’s not necessarily the most practical solution,” he says. “Going into an old pump and redesigning the hydraulic end of it and the impeller to optimize it for the most efficiency in that older design can be quite a challenge not to spend too much capital in doing that.”
Paul Scheihing, project manager in the Advanced Manufacturing Office of the US Department of Energy (DOE), currently works on the Superior Energy Performance program, a new DOE certification program for industrial facilities that focuses on continual improvement in energy efficiency. In the 1990s, he was the lead on a comprehensive study characterizing the energy efficiencies on industrial motor systems, including pumps, titled “United States Industrial Electric Motor Systems Market Opportunities Assessment”.
Another DOE program in the 1990s resulted in the development of tools, training, and a certification program, which is still utilized to this day, Scheihing says. One such tool is the Pumping System Assessment Tool (PSAT), a free online software tool to help industrial users assess pumping system operation efficiencies using achievable pump performance data from Hydraulic Institute standards and motor performance data from the MotorMaster+ database to calculate potential energy and cost savings.
DOE offers a qualification program for pumping system specialists in using PSAT. Qualified Pump System Specialists, of which Scheihing says there are a few hundred in the US, who can apply the tool to identify ways to improve pumping system efficiency. In the mid to late 1990s, DOE also conducted training for wastewater and water facilities, focusing on system efficiency opportunities.
“About 20% of the opportunity is in the component, and the other 80% is in system efficiency opportunities such as downsizing a pump or staging a number of pumps for operation when they’re in tandem or using variable speed, improving the overall pump system, making sure the pipe diameters are big enough, reducing turns and elbows, among other factors,” says Scheihing.
The same opportunities exist today, with savings from 10 to more than 50%, he adds.
“During the course of the day, the loads will change,” says Scheihing. “It could be seasonal. Many times, the systems are not being adjusted for those load changes. You end up with oversized equipment or equipment that is mechanically throttled, or, in some cases, the equipment might be old, and therefore, the efficiencies have degraded or are not as good as what you can buy on the market today.
“A lot of the savings focuses on the pump system,” he says. “A lot of the energy use in a wastewater treatment plant is aeration. That’s a big opportunity to properly optimize.”
In most cases, utilities are looking at anywhere from a 25- to a 40-year lifetime for rotating equipment with proper maintenance, says Bob Domkowski, business development manager for transport pumping and amusement markets and engineering consultant for Xylem Inc., Water Solutions USA—Flygt.
“There are going to be repairs along the way, but after a while, it’s time to consider upgrading and replacing,” he says. “It could be just replacing with in-kind equipment, and in some cases it’s nearly the exact same piece of equipment as put in place. Other times, there will be a search put out for what is state of the art: ‘How can we best arm this station for another 30 or 40 years of lifetime?’” he says.
There are several factors to be considered in retrofitting and upgrading pump systems, including knowing when is the best time to do it, and how to choose the appropriate technology. Once a pump has been identified for maintenance or efficiency improvements, the water utility must determine the most cost-effective course of action, says Potts.
“In some cases, it is more cost-effective to rehabilitate the existing pump; in other cases, replacement of the pump and/or motor is the better option,” he adds.
Potts outlines the factors that go into the decision-making process:
- The current operating range of the pump. Is it close to the best efficiency point?
- If the current operating range has moved away from the best efficiency point, then determine if the impellers can be trimmed or replaced to achieve operation closer to the best efficiency point.
- What will it cost to remove and reinstall a pump for rehabilitation?
- Will costly piping modifications be required to accommodate a new pump?
“Pumps and motors should be upgraded, rehabbed, or replaced when it can be shown that the energy cost savings as a result of the improvements will yield an acceptable payback period,” says Potts. “Since the vast majority of a pump’s life cycle cost is the energy cost, frequent rehab or replacement may be justified in many cases.
“However, operational constraints as well as limited water utility budgets and manpower suggest that a well-planned, long-term program of continuously monitoring pump performance and performing pump improvement work may be the best approach.”
Some utilities take a proactive approach, retrofitting a pump well before it needs it, says O’Toole.
“We get some pumps in for rebuilds or retrofits after 30 years, and the pump is perfectly fine and the customer knows that,” he says. “I equate it to when it comes to changing the oil in their car; there are some people who do it every 3,000 to 4,000 miles religiously because that’s what they were told to do, and then there are people who tend not to do that.
“Utility people are like that a lot,” he adds. “Sometimes it’s not because they want to be, but because they don’t have the money. To do things preventatively, you have to have the money in the budget. With what’s been going on in the US and the funding situation for municipalities, they have had to make some compromises in that regard.”
|Photo: THOMPSON PUMP
Adjustable speed drives continue to provide the most benefit for utilities.
There are other utilities, however, whose pumps are rebuilt every 10 to 15 years, regardless of whether the pump needs it or not because they know it’s the best approach, says O’Toole.
“There are other places that wait until there is a problem where they have some sort of water leakage, or they can tell efficiency has dropped off because they are consuming a lot more power than they used to,” he says. “The right answer is just like the car: do it on a set schedule that you’ve experienced. These utilities have been around a long time. They have the track record to know—based on their water conditions and their pressure and flow conditions—how often they should do it.”
When pulling out a pump for preventative work, that’s a good time to optimize the efficiency by changing the impeller, says O’Toole.
“Experience has been telling them that this thing has been running for 10 years, and they only need 90% of the flow they’ve designed for, so it’s a good time to redesign the pump, put a different impeller in it, and optimize it,” he adds.
Two significant changes in pumping systems technology have resulted in a significant improvement in efficiency, according to Potts. One is the National Electrical Manufacturers Association Premium Efficiency motors and the other is variable frequency drives (VFDs). While “premium efficiency” motors have been available since the 1990s, the Energy Independence and Security Act (EISA) of 2007 now requires general-purpose electric motors up to 500 HP that are manufactured after December 2010 be “premium efficiency”, says Potts. Premium efficiency motors have efficiencies in the range of 94 to 95% as compared to approximately 90% for “standard efficiency” motors, he adds.
In certain applications, it is beneficial to have the ability to vary the pump speed. Various types of mechanical and electrical variable speed devices have been used over the years, including eddy current drives and hydrostatic drives. The current state-of-the-art technology for varying motor speeds, VFDs, are significantly more efficient that older-style drives, achieving efficiencies of up to 97%, Potts says. For centrifugal pumps, Grundfos focuses on variable speed drives and controlling the speed of the pump based on demand, says O’Toole.
For the water distribution sector, Grundfos’ Demand Driven Distribution is a multi-pump solution operating at proportional pressure. The system is designed to supply the precise flow needed at the pressure required, with a number of pumps—instead of one large pump—running at the best efficiency point instead of one large pump.
“The big problem is you’ve got to boost the pressure up high enough, so everybody gets enough pressure so as you have leaky pipes, all it does is cause more leakage. When the demand is low during the middle of the day, if you can lower the pressure, you can really lower the amount of water that gets wasted,” says O’Toole.
O’Toole points out that in the US, water utilities tend towards large central pump stations. He’s learned much through exposure to the European design mentality, which he says is easier to optimize a system.
“Instead of having two pumps to pump this whole water flow and then have a backup, you have six smaller pumps,” he says. “Let’s say you need four of those to do that same job that two pumps could do. But when the demand is low, you only run two pumps and the third one can be a variable drive, so it’s two and half pumps.”
Because Europeans use a larger number of smaller pumps, they have the flexibility to deal with system variations, says O’Toole. Some of the US municipal water utilities have pointed out that there are tradeoffs, such as having more units to maintain and space considerations, says O’Toole. A modular approach allows for planning system growth, he adds.
“Knowing in 10 years, the system is going to be 50% bigger, you put in what you need now, and when you need more, you can add two smaller pumps to give that capability,” Says O’Toole.
As water and wastewater utilities seek to increase efficiencies through present-day technology, American Water has taken a proactive approach to leverage the company’s position and expertise to validate innovations using the company’s large and geographically diverse footprint to become an early adopter of new technologies for industry use through a program called Innovation Development Process (IDP), says Potts.
“The IDP identifies and develops ideas which drive efficiencies into American Water’s existing regulated and market-based businesses while identifying opportunities that increase shareholder value,” he says.
The IDP provides a conduit for innovators to allow their technologies to be evaluated and to accelerate the adoption and market penetration of products or services that help solve pressing needs within the water industry, Potts says.
American Water recently announced its partnership to a two-year $1.8 million award from the Israel-US Binational Industrial Research and Development (BIRD) Foundation along with Steam Control Ltd. for the development of an advanced pressured management system. The research project demonstrates the feasibility of installing modifications on existing pressure system controls that could reduce pressure in a system in response to reduced customer demand.
International efforts to reduce leakage have confirmed that reducing excessive pressure not only reduces the volume of leaks through pipes, but reduces the frequency of pipe failures, says Potts.
“The expected outcome of the project will enable average reduction of water leakage significantly,” he says.
With respect to pumps that handle wastewater, one of the biggest challenges today for all utilities is handling flushables, notes Domkowski.
“Wipes have been causing them headaches for quite some time now,” he points out. “That goes towards the energy efficiency and the retrofitting.”
Much of the utilized technology is based upon hydraulic designs that date back to 1915, and from the 1950s, when A. Baldwin Wood invented the Wood Trash Pump.
“That was great for handling wastewater up until the 1970s and 1980s, but then utilities were challenged with these flushables that are creating a huge problem for maintenance costs as well as efficiency in that the impellers of these designs of these pumps get partially clogged with soft solids like cleaning pads, wipes, and things like that,” says Domkowski.
What should take a lift station five or 10 minutes to accomplish ends up taking a half hour because the impeller can no longer operate at its best efficiency.
“That’s been a challenge people have been seeing for quite a while and is growing exponentially,” says Domkowski, adding that the solution to the challenge most likely will come through adding better screening as efforts to educate the public have fallen short of stemming the tide of the growth of the trend.
Adjustable speed drives continue to provide the most benefit for utilities, Domkowski says.
“They are great in assisting and providing energy efficiency,” he points out. “Some of the newer ones are smart drives. We have one product in our drive system where data on the actual performance curve and characteristics of the pump are in a lock box in the pump drive.”
When the pump is activated for the first time, the drive determines how long it takes to empty a wet well, Domkowski says.
“The next time it turns on, it will start at two hertz lower speed and see how long it takes to empty the wet well and measure how much energy was used,” he says. “If it uses less energy, the next time the drive starts, it will start two hertz slower even further, and it keeps on doing that until it gets to the point where it costs a little bit more to empty the wet well that time, so it goes back the other way. It’s constantly searching for the best operating position.”
Energy savings is the primary benefit, Domkowski points out.
“You have a fixed-in-place pipe in the ground. If you are running full speed, and you’re fully charging that pump or that pipe and you have a certain head loss which costs energy to over-pump if you push less water to that pipe, it costs you less because you’re not having as much pressure and pressure is what costs you in pumping,” he says.
“Putting less water through may take slightly longer to do, but there’s less head, so the overall cost of energy to accomplish that task is lower. The drive is looking for the least expensive way to pump this water out.”
There can be an energy savings benefit of 40 to 50% over traditional solutions with this system and an impeller that can handle modern trash concerns, says Domkowski.
The D grade from the American Society of Civil Engineers (ASCE) is indicative that when it comes to underground utilities, for the public it’s “out of sight, out of mind,” says Domkowski.
“For utility operators and directors, it’s a challenge to stretch the funding and ratepayer income dollars across whatever has to be done and in some cases, it’s becomes a Band-Aid,” he says. “Whether it’s on the collection system piping or the equipment, there are many types of challenges for continuous operation.”
One such challenge is getting the ratepayers to a level of understanding that “pay as you go” has to be increased, he says.
“No one likes to see an increase in usage rates, but that is critical in sustaining our underground infrastructure and keeping it problem-free,” says Domkowski. “We don’t want to have these expenditures made because we’re under an EPA edict that something has to be done because we are not complying.”
“It goes back to the wipes again for the overall station health,” says Domkowski. “Can I put some type of screening in to remove this debris before it gets into my collection system? There may be equipment out such as pumps that can move this debris along confidently, but do I want these things in my collection system?”
Author’s Bio: Carol Brzozowski specializes in topics related to resource management and technology.