By Allison Deerr

How do you size a high-efficiency pump? It depends on who you ask.

It seems that smart pumps are sized the same way as constant-speed pumps. The factors in pump sizing remain the same: static head, friction head, pipe length and fixture count. And yes, it does matter what the application is, what kind of a system we are talking about and what kind of conditions it will operate under.

It may just be a matter of semantics whether you are sizing a pump for a particular application or selecting the right pump for the project. One thing everyone seems to agree on: Whether you call it a high-efficiency pump, smart pump or intelligent pump, these variable-speed pumps with integrated control mechanisms offer energy efficiency and built-in flexibility over a traditional one-speed.

Variable-speed-drive pumps tend to be more of a one-size-fits-all approach, says Mark D’Agostino, former president of Wilo USA. When you have a constant-speed circulator — even one that is advertised to be a two-speed or a three-speed pump — you have a fixed duty point. In its best operating point, the constant-speed pump will do a fixed amount of head and a fixed amount of flow.

“With Wilo smart pumps, you can dial in the amount of head you want the pump to overcome; you simply turn a dial to increase or decrease the head set point,” he explains. “So it allows the pump to be very specific to a duty point, and the duty point is selectable. Then, when you look in a typical pump curve, the best efficiency operating area for a circulator is in the center third of the curve. With a variable-speed-drive pump, the pump is equally efficient anywhere in its operating range.”

A good rule of thumb would be choose the smallest pump that will do the job you need it to do, D’Agostino adds. For example, if you need 30 ft. of head at 30 gal. per minute, the smallest pump will be the most efficient because it will consume the least amount of power.

“Currently, the way constant speed pumps are operated, we floor the gas pedal and try to regulate the speed of the car with the brake pedal. You find yourself not having very good utilization of your fuel economy,” D’Agostino says. “With a variable-speed smart pump, the pump acts as cruise control. If you need to accelerate to go up a hill — be bigger for the future — you can … simply turn the pump up to address a higher demand. But when you’re on a flat stretch of highway and you want to … maximize fuel economy, the pump will ratchet itself down to do that kind of ‘driving’ as well.”

There is no real difference when it comes to sizing a pump, whether it’s a continuous drive or high efficiency, notes Mark Chaffee, marketing director of residential products at Taco. If you are using a pump for sump, snow melt, domestic hot water or regular heating, each of those has different variables that go into the setup, the mode you might choose. You’re figuring out, OK what pump should I put on this job?

“From a sizing standpoint, it’s identical. There’s nothing magical about it,” he says. “The point that is probably valid here is that the sizing is the same, but programming and understanding what the programming means is what’s important. People label or cross-term high-efficiency pumps as ‘smart pumps’ because there is some sort of circuit board or intelligence, something that’s making the pump vary its speed, either a variable-speed drive or an internal sensing circuitry which turns into a variable-speed pump. … But [the installer] still needs to understand the application and how to program the pump for that application.”

Oversizing for future capacity

With the traditional, nonintelligent pump, oversizing was a major problem, explains Brent Ross, director of configured equipment/standard building products at Armstrong Fluid Technology. When sized to meet a demand you might have in the future, the pump took more power and caused more wear and tear on the system.

“With intelligent pumps, their nature is to be able to operate efficiently and effectively over a larger range of operation,” he says. “In the traditional world, oversizing pumps means you’re drawing more power and pumping more liquid than the system needs. That’s a very basic observation. For systems that have the control means, they control the pump by throttling, which means that you’re wasting energy. New intelligent pumps are able to adjust their output to match system requirements without wasting energy, without requiring the control valve to throttle substantially, without causing wear and tear on the system, without drawing excess energy.”

Joe Rice, product manager of large circulators at Grundfos Pump Corp., says: “Generally speaking, you can say that there’s no difference in sizing and selecting. The typical method of sizing is to look at the peak demand and the friction loss in the piping to meet that peak demand, then pick a circulator that achieves that. When you are talking about a variable-speed pump or a variable-flow pump, in any application where the load is changing and there is this big demand, the reality is that the peak demand doesn’t happen all the time.

“Ideally, you want to pick a pump where that peak demand in the pump curve is on the right-hand portion of the curve, right of the best efficiency point, because that point doesn’t often happen.”

One of the key advantages to the variable-speed pump is that you can intentionally oversize the pump for a future capacity, Rice notes. You can change the pump performance to match what the system needs really are. If the variable-speed pump is oversized, it “sizes” itself. It slows down and basically changes its own pump capacity or pump size to match that system.

“Having that ability to trim the pump via electronics and let it slow down and only use what’s needed and still have that capacity there for future additions is absolutely a benefit,” he adds.

The smart pump is sized differently, D’Agostino adds. It moderates the speed based on actual demand, not some theoretical demand on paper. “The pump modulates to a speed to deliver what is required right now in the real-world life of that system,” he says. “It’s like having the equivalent of a 5 hp pump if you need it, but today you are only using 2 hp. It’s there and available … when the demand requires it.”

However, you are paying for more pump at first cost. You’re buying a bigger pump than you may actually need for some proposed or potential future use; that’s the only downside to it, he adds.

“A lot of customers will buy the larger pump so they’ll have the flexibility in the future,” he explains. “But right now, you are only paying for the consumed power to operate the pump today, not what its maximum capability would be. At Wilo, we call it the layering effect, because you get multiple benefits.”

Additional benefits

Because of the huge focus on energy usage now in a lot of commercial buildings, there is an increase in electronic monitoring — because if you’re not measuring it, you’re not managing it, Rice says.

“You’ll see a lot more buildings having monitoring systems in place,” he notes. “By putting all that monitoring directly into the pump, you end up with just one data point or point of contact for that building management system, which reduces costs associated with all the communications equipment [building owners] install to monitor all these data points. With one data point, you provide nearly full system information.”

A smart pump offers several advantages. “It only runs when you need it and at the capacity that you need,” Rice explains. “The variable-speed pump is softer on the system because you aren’t having these immediate changes in demand. The valves still are opening and closing, but they are gradually ramping up and slowing down rather than a hard on or off.”

 Ross adds that the soft start, along with the ability to throttle down and not run all the time at full capacity, greatly reduces not only energy use but also the wear and tear on the pump, therefore extending the life of not only the pump, but the entire system into which it is integrated.

Another benefit is little to no maintenance. “With the integrated drive effectively on a soft start, you don’t have any high inrush currents on the electrical system,” Rice says. “[And] being wet-rotor-type pumps, they are maintenance-free. You don’t have the 18-month or 24-month service cycle going out and changing seals or bearing assemblies. Install it and there’s no maintenance on the pump for the life of the pump, 15 years or more.”

 Manufacturers are working to make adding smart pumps to the mix less intimidating. Installers and contractors shouldn’t fear the new technology.

“The industry over the years has created products with a fixed duty and a fixed speed, so there was very little margin of error as to having the right pump or the wrong pump,” D’Agostino explains. “I think that’s created an intimidation factor in the pump world. The expertise has been pushed off to the distributor, who then is concerned about his exposure and may push it back to a technical support team with a manufacturer. So the beauty of the high-efficient pumps is there is no risk. The pump can be very precisely field-adjusted for almost any application.

“We do count on the contractors being savvy, understanding systems and being experts in what they do. The point is they don’t have to be expert in all of the intricacies that make the pump run and the programming logic that happens when they push that red button. We’re ensuring that they get maximum life cycle, maximum energy efficiency, and ease of use simply by adjusting that red button to whatever their field demand is.”

Rice agrees: “It’s a proven technology. … They have higher reliability, are easier to install and use, so there is no need for the fear factor.”

Training and education with the manufacturers is a very important, Chaffee says. “Taco offer a whole host of classes via our Flo-Pro University online education,” he adds. “We offer an entire course just on variable-speed pumping — why to use it, how does it work, what you might need for different applications. It’s a great resource.”

This article was originally titled “Size matters” in the July 2015 print edition of Plumbing & Mechanical.

Author bio: Allison Deerr is a freelance writer in Anaheim. The original version of this article appeared in the June 2013 issue of Reeves Journal.