advertisement

Centrifugal Pump Design

Centrifugal pumps are used to control the built environment in a variety of ways.

Pump physics and basic mechanics have not changed significantly over the last century. However, in recent years, the state of the art in pump application has dramatically improved. Nonetheless, pumps are frequently underutilized and are common targets in retro commissioning projects where field assessment and testing can reveal significant energy savings potential from optimizing pump performance. Typically, retro commissioning reveals that pump flow rates do not correspond to their intended design intent, and that lowering flow rates to match load requirements or eliminating unnecessary pressure drops can save energy. As the example below shows, decisions made during the design phase have long-term consequences for the building's operation.

Although fully optimising any design will require some effort after installation, the prevalence and magnitude of the savings 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?

advertisement

Brake Horsepower (BHP): The power required as an input to the pump shaft to deliver the indicated flow and head is referred to as brake horsepower. Brake horsepower considers pump efficiency but not motor efficiency. To account for losses in the motor and drive system, divide the brake horsepower requirement by the motor and drive efficiencies at the specified operating point.

Pump System Power Terminology The power used or generated by a pump is described using several terms:

Motor Power: The amount of power delivered to a driven device by a motor shaft. This is the motor's "size," for example, "1/2 horsepower motor."

Motor power input: The amount of electricity drawn by the motor, as displayed on the electric metre in kW.

advertisement