Pumping systems efficiency improvements flow straight to the bottom line Page: 3 of 5
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far outweigh the sum of the savings through component
Generally, it is neither feasible nor prudent to
analyze each pumping system in a facility. However,
the DOE BestPractices program has developed a
guideline for prescreening pumping systems for
potential energy savings. The guideline provides a
methodology that can help to identify and prioritize
candidate systems for optimization. This prescreening
guideline includes sample data collection forms, and
can be downloaded at www.orfl.gov/etd-
Once the prescreening process has identified
pumping systems with potential cost savings
opportunities, the Pumping System Assessment Tool
(PSAT) can be used to further screen systems and
quantify the potential savings. The PSAT software was
developed for DOE as a tool to assist end users (and
others) in assessing the overall effectiveness of
centrifugal pumping systems (Ref. 4). PSAT is
available at no cost through the DOE BestPractices
program web site (www.oit.doe.gov/bestpractices/).
The prescreening guide noted above is included in the
Assessing opportunities for improvement, whether
using PSAT or some other methodology, will require
relatively accurate measures of flow rate, pressures, and
electrical power. These quantitative measurements
must be considered in the context of qualitative data
obtained through interviews and discussions with the
pumping system operators, visual inspections, and
review of operator logs (if available). A more thorough
discussion of measurement guidelines can be found in a
series of articles from the DOE BestPractices' Energy
Matters newsletter (available from the BestPractices
PSAT estimates the existing motor and pump
efficiency using field measurements and nameplate type
motor and pump information. PSAT makes use of a
Hydraulic Institute (HI) standard that provides guidance
on achievable pump efficiencies for numerous pump
types (Ref. 5). It also estimates achievable efficiencies
if the motor and pump were optimally selected to meet
the specified flow and head requirements. The
"existing" and "optimal" results are compared, and
potential power savings are determined. Finally,
potential cost and energy savings are estimated based
on user-specified power cost rates and operating times.
PSAT results are useful in identifying the
approximate energy and cost savings that could be
achieved if the existing pump system was optimized.
PSAT does not identify how the savings can be
achieved; in other words, it is not a solution provider,
but rather an opportunity identifier.
PSAT does not require the user to be a fluid system
or pump application expert, and even users with little
pumping system experience can get useful results from
the program. However, in the hands of a user with a
good working familiarity of pumping systems, PSAT
can be used to perform "what-if' evaluations that can
actually assist in system design.
A PSAT workshop developed for DOE is offered
at various times, by both DOE and its Allied Partners.
The BestPractices web site regularly lists upcoming
TURN OPPORTUNITIES INTO SAVINGS
The results of a systems approach to analysis will
vary from system to system and from facility to facility.
Some of the more common indications of an
opportunity and common modifications are described
Sizing -- A system with highly throttled control
valves or extensive use of bypass lines can be an
indication of an oversized pump. Oversizing is a
common problem, and may be the result of
conservative design, design for anticipated system
capacity increases, or a decrease in the output demand.
Possible improvements are to trim the existing pump
impeller, install a smaller impeller, remove stages of the
pump (if a multi-stage pump), replace with a smaller
pump, or reduce the pump speed.
Replacing the pump with one that is better suited
for the system requirements can provide efficiency and
performance improvements. Opportunities for this
change include events where the pump must be
removed for overhaul or repair. In fact, the cause of a
pump replacement may be largely attributable to
initially poor pump selection. An oversized pump that
operates far off its best efficiency point (BEP) tends to
suffer accelerated wear. Consequently, if the pump
must be replaced due to premature wear, assessing
whether the pump was correctly sized in the first place
is advisable. A petroleum refinery has recently
documented savings of $700,000/year through a
combination of measures on several large, oversized
pumping systems (Ref. 6).
In systems where flow requirements vary, but the
flow rate is either not controlled, or is controlled by
valve throttling or bypass flow control, speed control
devices can provide attractive energy savings. The
pressure drop created by the throttle valve causes an
energy loss and, if the restriction is severe enough, can
create significant flow noise and valve seat wear. Since
bypass lines divert flow, the pumping energy spent to
generate the bypassed flow is essentially wasted.
Speed reduction can be achieved by changing
sheave diameters (in belt drive applications), installing
a slower speed motor, or installing an adjustable speed
drive. In general, such modifications may be feasible if
the pump output is consistently higher than the system
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Tutterow, Vestal; Casada, Don & McKane, Aimee. Pumping systems efficiency improvements flow straight to the bottom line, report, July 8, 2002; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc882487/m1/3/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.