As mentioned earlier, proper impeller trim, pump size, and operating point are all important to best operational efficiency. (Note: With fluids other than water the specific gravity of the fluid has an effect on the BHP.)Īs a heating-cooling system may operate at full load for only a small portion of a given day, if the pump speed can be changed, more of an energy savings can be achieved than worrying about a few +/- points on pump efficiency. The electric motor driving the pump also has an efficiency factor, so to determine the operating cost we would factor in the motor by BHPX. This formula can also be used to predict the operating cost. The BHP can be calculated from the formulaBHP= Q X H X Sp Gr. The further you get away from full size diameter, there will be a drop in efficiency, but the reduction in horsepower due to a lower head should offset this efficiency drop. Decreasing the diameter of the impeller from full size does reduce the head, flow and BHP. Replacing the RPMs with the impeller diameter will follow the same rules. You can see from the Brake Horse Power formula that theBHP changes with the cube of ratios of the speeds, which is a big energy savings for a small change in speed. The Affinity Laws are RPM 2 / RPM 1 ) X GPM 1 = GPM 2, ( RPM 2 / RPM 1 ) 2 X H 1 = H 2, ( RPM 2 /RPM 1 ) 3 X BHP 1 = BHP 2 Throttling the pump adds additional resistance to the system to control the pump and is not as efficient as reducing the speed or diameter of the impeller. If a pump has excess performance, a greater energy savings can be achieved by using a variable speed drive or correcting the impeller trim to match the system resistance. These laws can be used to predict the performance of a pump at a reduced speed or smaller diameter impeller. These laws explain the change in performance of a pump when the speed is changed or the impeller diameter is changed. Pumps are variable torque machines that follow the Affinity Laws. Higher flows will increase the NPSH required and erosion due to cavitation could result along with an increase in noise and vibration. Operating a pump at less than or more than the BEP will lower the operational efficiency and placeĪdditional stress on the pump shaft and bearing due to increased thrust and radial load. A pump should be selected so that it will always operate near its BEP. This is called the Best Efficiency Point (BEP). George Taber, a 38-year veteran of Taco, Inc.īy George Taber – Applications Engineer-Technical Services Supervisor, Taco, Inc.Ĭontinuing our discussion on factors affecting pump efficiency, let’s discuss pumps and their BEP or Best Efficiency Point as well as fluids viscosity.Ī centrifugal pump is designed for best performance at a head and flow at a certain speed.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |