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e nergy design resources

design brief

CENTRIFUGAL PUMP APPLICATION
AND OPTIMIZATION
A pump that is well-sized,
-specified, and -selected, and is
operated in a manner that reflects

Who Should Read This Brief?

the design intent will be more

This brief presents practical pump theory, selection and application principles. The concepts discussed will be of interest to:
Design professionals who want to better understand how pump

theory and design practice apply to day-to-day operating

efficient and often costs less
than a pump that does not fit the
needs of the system it serves.

environments
Commissioning providers who wish to better understand pumps,

pumping systems, and the evolution of design intent for hydronic systems
Facilities engineering professionals who want to better understand

the fundamental design and application principles behind the equipment they operate
Key points for each of these areas of professional practice are emphasized

contents

in checklists at the end of each major topic.

Summary

2

Pump Energy

3

Selecting Pumps

22

Optimizing Performance

37

Specifying Pumps

44

Conclusion

46

References

47

Summary
Centrifugal pumps perform many important functions to control the built environment. The physics and basic mechanics of pumps have not changed substantially in the last century. However, the state of the art in the application of pumps has improved dramatically in recent years. Even so, pumps are still often not well applied, and become common targets in retrocommissioning projects where field assessment and testing can reveal significant energy savings potential from optimizing pump performance. Typically, retrocommissioning finds that pump flow rates do not match their design intent and that reducing flow rates to match load requirements or eliminating unnecessary pressure drops can save energy. As the example below illustrates, decisions made during the design phase have implications throughout the operating life of the building.

Although fully optimizing any design will require some effort after installation, the prevalence and magnitude of the savings that are commonly found in retrocommissioning and ongoing commissioning begs the larger question: How much greater would the savings be if pumps were selected and applied optimally during the design phase?

A Common RCx Problem Reveals Missed Opportunity for Rightsizing The pumping application shown below illustrates a typical less-

The pump selected for the application was rated for 40 feet water

than-optimal design that often translates into a retrocommissioning

column (ft. w.c.) of head at the design flow rate, even though the

opportunity later on.

piping circuit it served was very short with very few fittings. Field testing revealed that only 13 to 14 ft. w.c. of head was actually

Centrifugal
seperator

required. During RCx, the pump was optimized to the requirements

1200 gpm @
40 ft.w.c.;
20 hp motor

of the system via an impeller trim and minor throttling. However, many other opportunities were missed because the system performance was not optimized during the design phase. If it had been, the pump selection would have more closely matched the needs of the system and would:




Be smaller and cost less to purchase and pipe;



Page 2

Operate at its best efficiency point in the as-built system;

Require a 10 hp motor and electrical service instead of 20 hp.

A Field Perspective: Centrifugal Pump Application and Optimization

This brief tries to answer that question by exploring the theory and reality behind the selecting and applying centrifugal pumps in commercial buildings. You will learn that if a pump is carefully specified during the design process and is installed in a manner that reflects the design intent, it will be more efficient and will most likely cost less than a pump that does not fit the...
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