“Variable frequency drives (VFDs) are valuable technology, and they always save energy in water and wastewater system pumping.” The first part of that statement is true, and the second part is generally true but not always. There are exceptions that engineers and operators need to be aware of when they are buying and operating pumping systems. A question I frequently pose is: “What is the best speed to run a variable speed pump?” I receive a variety of responses, but the correct one is, “Off.” If you can select a pump that operates at an efficient operating point, allowing it to run near its best efficiency point (BEP), it will outperform a variable speed pump which tends to have fluctuating operating points along the pump efficiency curves (Walski et al., 2001). ApplicationTurning pumps on and off requires storage to meet demand when the pumps are Off. In water systems, pumped flow is often directed to elevated tanks, which allows the tanks to be filled and drained with constant speed pumps. This has the added benefit of turning over the water in the tank improving disinfectant residuals. In wastewater systems, the storage occurs on the suction side of the pump, with

Engineers and scientists love graphs. With one image, they can convey as much information as many pages of text and do it in a way that can be clearly visualized. Nowadays, with software, we can do so much more with graphing, but that’s not always the way it was done. Here is how simple graphs used to look like in the past, drawn on preprinted graph. Straight line y=mx+b Here is a graph you can get from Excel today: Sure, anybody can draw a graph on arithmetic graph paper. But what happens when you have data that cover several orders of magnitude and data aren’t very evenly spaced. You could take the logarithm of each point and plot it that way, but then you would need to continuously convert the data from the log scale to your original values. For example, “the graph says 3.52 but that’s the log of the real value that is 3311”. The key of course is to have graph paper with logarithmic scales. Your graph paper would look like this: The figure shows 3 cycle log-log paper. Straight line y = aXb In Excel the figure could look like this: Sometimes, however, only one axis

For academic researchers, “Impact Factors” is a familiar term – it is designed to measure the impact of your publications. If you are outside of the academic world, you have probably never encountered it, but how much do these metrics really tell us? Impact factors emerged as a way to compare research papers. Academia often measures a researcher’s success by the number of publications, which influences tenure and promotion decisions at universities. The problem was that not all journals and papers are of the same quality. Universities needed a way to determine the caliber of research without having to actually read every paper. The solution? If a paper was cited by other researcher within a few years of publication, it is assumed that the paper and the journal it appears in must have an impact. Over time, this has evolved into a formal system for calculating Impact Factors, with journals proudly listing their scores. To judge individual papers, metrics like “categorized-normalized citation impact” were developed using similar logic along with a “percentile group” score to compare a researcher’s work with papers in a similar field. But I question: “impact on whom”? I feel that the impact of a paper in

When precipitation falls on land, in the short term, there are two places it can go: runoff to streams or infiltration into the ground. In the long term, evaporation also matters, but during a precipitation event, it isn’t important. Runoff enables water to be used for a variety of purposes as it makes its way to the ocean. Along the way, however, it contributes to flooding, erosion, and is usually moving too fast to be captured. From an environmental and water efficiency standpoint, it is generally better to have most of the water infiltrate into the ground, reducing flooding, nurturing plant life, and later contributing to base flow in streams, flattening out runoff hydrographs. But first, a digression that always troubles me: “What is infiltration?” There are at least two answers: In hydrology and some hydraulics, infiltration is the precipitation that makes its way into the ground. However, if you’re talking about sewers, infiltration is a subsurface water that leaks into sewers when it shouldn’t (i.e., the I part of I&I). The first infiltration is generally a good thing; the second is a bad thing. The result is sentences like “Infiltration into the subsurface can result in additional infiltration into

Seminal papers are groundbreaking at the time of publication and remain influential many years later. I recently received word from the ASCE that my paper, “Battle of the Network Models: Epilogue,” published in the Journal of Water Resources Planning and Management, Volume 113, No. 2, 1987, has been selected to receive the Journal’s 2024 Seminal Paper Award. Here’s the story behind it if you are interested. In the early 1980s, many papers were being published on optimal pipe sizing in water distribution systems. It was hard to compare the methods. At that time, there was a television show, “Battle of the Network Stars,” where various TV stars would compete with one another in various little “athletic” events. The show ran from 1976 through 1988. I thought that would be a good name for a conference session and paper that I called “Battle of the Network Models.” I drew up a pipe network called “Anytown” and sent it out to everyone working in this area. We had a series of sessions at the ASCE Water Resources Planning and Management Conference in Buffalo, New York, in 1985 that brought together many of the top people in the field. I wrote the summary

Back in the dark ages (e.g., the 1980s) before everyone had video capabilities on their cell phones, creating a training video was a big production. Video cameras (and their batteries) weighed about 30 pounds and editing tools we crude. I was doing a lot of flow testing in those days while working for the Army Corps of Engineers at the Waterways Experiment Station (WES) in Vicksburg, Mississippi. I had some money available and wanted to capture not only the mechanics of flow testing, but how to use the results of such tests in modelling. I didn’t want this to be a boring video with me as a talking head with a shot of a flow test. This was also a at that time, MTV was becoming very popular (Remember when MTV played videos? At least I hope some of you do.), so I wanted to use a lot of short scenes interlaced with music (and perhaps a little humor). This is how I became the writer, producer, director, and narrator for a training video on hydrant flow tests. I was shooting for something like historian James Burke’s “Connections” series for engineers. https://en.wikipedia.org/wiki/Connections_(British_TV_series) The video production came down to a couple

AWWA recently announced the release of the fourth edition of its popular manual, M22-Sizing Service Lines and Meters. You might be thinking, “What could be new in sizing service lines?” For the most part, not much has changed, but there has been a major update to the way that residential peak demand is calculated. If you only have a single fixture in a building, then the peak demand in the building is the same as for the single fixture. If you have two fixtures, just add the demands. As the number of fixtures increases, however, the chance that all will be running at the same time decreases. This problem was solved nearly a century ago by Roy B. Hunter of the National Bureau of Standards (Hunter 1940, 1941) who developed an expedient method based on the Binomial theorem and flows from typical water fixtures from the 1930s. The result was the widely used Hunter’s Curves that related the peak water demands to the number of fixture units. The iconic Hunter’s Curve worked so well that it was quickly incorporated into many plumbing codes around the world. Over the years, however, the Hunter’s fixture unit concept has been modified by various

The term given to this process is “Daylighting” (although the term gets used in a lot of other situations). The American Rivers organization is one of the leading groups in the U.S. that promotes stream daylighting. Their definition is, “Stream daylighting revitalizes streams by uncovering some or all of a previously covered river, stream, or stormwater drainage.

I often title my blogs with a question that I’m very happy to try to answer. “What’s the Capacity of That Pipe?” is not one of those questions. Unless you make some simplifying assumptions such as “The pipe is flowing at normal depth” or “The full pipe velocity is 5 ft/s,” the real answer is elusive. I usually respond with a litany of questions, including “Why are you calculating this?” and “What assumptions are you willing to make?” The most important distinction is whether the pipe is designed to flow full, like a water distribution pipe, or a sewer force main, as opposed to a gravity sanitary, combined, or storm sewer. Therefore, there is a two-part answer to the question in this blog but they both go back to this simple equation: Q = A V Where Q = flow (and in this case capacity), A is the cross-sectional area occupied by the flow, and V is the velocity. Such a little equation for such a big concept. Regulatory/administrative people like to treat the capacity as a fixed number. If someone says the capacity is 500 gpm, and you want approval to use the pipe to move 499 gpm, you

Work on the upcoming AWWA Manual on Energy (M83) is wrapping up, and I’ve been working with Eric Dole, National Water and Energy Practice Lead for Garver, on the pumping chapter. It’s shaping up nicely. One topic that has come up is: What’s the best metric for judging if a pump or a pump station is working well vs. one that is wasting energy and money? There are quite a few potential metrics, and they all have their strengths. The definitions vary, but the most common are: Efficiency Energy intensity Or, in some cases: Where e = efficiency, Q = flow, h = pump head, P = power, i1 and i2 are two different formulations for energy intensity, and the k values are unit conversion factors that depend on the units used. Efficiency can either be pump efficiency or wire-to-water efficiency. For pump comparison, it is best to use wire-to-water efficiency because it accounts for motor and drive efficiency. We can solve these equations simultaneously to give: Or Essentially, energy intensity is just the inverse of efficiency. Efficient pumps have a low energy intensity. The difference between i1 and i2 is that i1 has a worse intensity for pumps discharging