Centrifugal pumping systems are commonly found at water and wastewater treatment facilities. The performance capabilities of these pumps are often interpreted by analyzing graphs that have two curves—one curve representing the pump’s head capacity and the second the system’s requirements. On these supply-and-demand graphs, the system curve slopes up, and the pump curve slopes down. Due to conservative design or regulatory requirements, pumping systems are often oversized, and thus operate inefficiently. In cases where an imbalance exists, there is often an opportunity to improve the pump’s operation and cost efficiency. To do this, the first step is to identify if there is in fact an imbalance between what the pump supplies and what the distribution system demands.
When looking at a graph measuring a pump’s performance, the system operation occurs at the intersection (I) of the supply (pump) curve (P) and the demand (system) curve (S). This is the point at which the resistance to flow in the system is matched by the fluid power the pump produces.
To reduce a centrifugal pump’s energy consumption, it is necessary to either reduce resistance to flow in the system (which will result in a change to the system curve on the graph), modify how the system operates, maximize the efficiency of the pump producing the flow, or perform some combination of the three. Figures 1-3 show how pumping energy goes down when operating points or system resistance are reduced.
Best practices for reducing energy consumption include:
- clearly define the intended goal of the system
- determine the head and flow rate required to achieve the goal
- supply only what is necessary to achieve the intended goal
What about Efficiency?
While replacing degraded equipment with new equipment can make significant efficiency improvements, it is imperative that any equipment—old or new—be correctly sized. Practice shows that matching supply to demand is often more important than ensuring that individual components operate at peak efficiency.
For municipalities that may not have extensive engineering resources, a pumping system analyst can help identify and quantify opportunities for pumping system optimization. For technical support on optimizing energy consumption at water facilities and other energy-related issues, Technical Assistance is accessible through the Solution Center.
Content for this Blog post courtesy of Daryl Cox, Oak Ridge National Laboratory