I received a lot of feedback on my column “How Much Energy Do Pipes Remove?” in the September issue of Pumps & Systems. This column described the use of two computer programs that evaluate the effects piping has on pump energy and the associated costs of those effects. The two programs have been reported as effective tools for estimating pipe friction losses and calculating the pump and motor energy required to move the flow at a pump head required to overcome the friction in the piping. The resulting motor power at the assumed cost of kilowatt-hour energy provides the yearly energy cost. The program has now been modified and expanded to include the ability to compare new and old pipes, as well as estimate the percentage of time a pump operates throughout the year. One example comes from Lee Ruiz, who often offers excellent and insightful comments regarding my articles. To get the most from Lee’s comments, I recommend you read the original article.
Letter from a Reader
The following comments relate to the calculator/estimator programs and ending question in your September 2014 article, “How Much Energy Do Pipes Remove?”
The pipe length shown is about 150 feet short of 5 miles (but close enough).
The friction losses calculated by the Energy Consumption Calculator seem to be about double what I would expect for relatively clean water flowing through a reasonably new pipe. However, the calculated friction values may be appropriate for the partially clogged piping scenario (or if initially designing for aging pipes).
It might be useful if the energy calculator displayed a range of possible friction losses, power
and cost that reflect new and old piping systems.
Per the consumption and performance programs, the half-area partially clogged piping would result in a much greater friction loss at 8,000 gallons per minute (gpm). That is, the original pump would need to produce an approximate 5.7 times greater head (and discharge pipe pressure).
It would also require an impeller approximately two times larger; it would have a very low efficiency, and it would require about seven times the original power. Therefore, a single, larger one-stage pump was not considered.
Again, by using the consumption and performance programs, one six-stage pump and six one-stage series booster pumps were each evaluated for potential use. However, the six-stage pump was not given serious consideration because of the high discharge pressure and stress it would impose on most of the existing piping system.
Using the total pipe length of 26,250 feet and pipe inner diameter (ID) sizes of 18 and 20 inches, the following additional energy amounts were determined by using the Energy Consumption Calculator and the Pump Performance Estimator.
The six-stage “high discharge pressure and pipe stress” values are included for reference (see Table 1).
Table 1. Energy amounts using the Energy Consumption Calculator & the Pump Performance Estimator
Of course, for a clogged piping system using staged or booster pumps, additional installation, pump, motor, piping and maintenance costs would also need to be considered. The total costs can then be compared to keeping the existing pump and repairing or replacing the clogged piping.
The Energy Consumption Calculator and the Pump Performance Estimator programs turned out to be useful for an approximate evaluation of the piping systems: pump-magazine.com/pump_magazine/pump_magazine.htm.
Lee Ruiz
Oceanside, California
Table 1. Energy amounts using the Energy Consumption Calculator & the Pump Performance Estimator