Does anyone have any logic examples of a SAMA drawing that represents programming pump curves into the PLC/DCS so that we can operate our multiple pumps at the most efficient points? In other words, when we start running out on a curve for one pump it uses more electricity. Therefore it may be reasonable to cut on another pump before we get to that point. Maybe we could just do it on flow?? Brainstorming here.

 

There are problems in your plan. First, most pumps are designed to operate at either one of two different constant speeds dictated by the frequency of the AC power to the electric motor driving the pump. You will find pump curves plotting pumping volume vs. head for a given rotational speed and impeller size. While they may exist, I have never seen a pump curve for variable speed vs. head or volume. The most energy efficiency for a flow control system can be obtained by physically removing the control valve and all but the most essential valves in the piping network. The pump itself can support a turndown ratio larger than that you can get by using a control valve, however, operation at low flow rates may require such slow pump rotational speed that the electric motor fan cannot sufficiently cool the electric motor. In this case, the pump impeller size may need to be reducedto increase the speed of the motor rotation to get adequate cooling. Using a VFD also causes the drive motor to require additional cooling due to the need to remove the harmonics resulting from the VFD generated simulation of a sine wave using pulse width modulation.

You should also become familiar with the pump affinity laws: see
http://www.engineeringtoolbox.com/affinity-laws-d_408.html

Dick Caro

 

Please explain in detail, the process using multiple pumps.

do you have variable loads?