This study is aimed at evaluating the optimal number of pumps required to operate a pumping plant efficiently to obtain a maximum energy savings. One of the evaluative problems being faced currently by the Ghana Water Company Ltd at Akim Oda water treatment plant is the high-energy consumption as a result of the use of single pump in the operations. Since commencing operations in 2018, the system had comprised of five pumps and VFDs integrated with a PLC and SCADA. In motor life cycle, pump cost is 10% and energy consumption 90%, thus considerable improvement in energy savings is possible by increasing the energy efficiency of the pumping system. The main problem with these induction motors is their high-power consumption. In the present study, modelling, simulation and performance evaluation of a variable frequency drive using Matlab/Simulink model was carried out. The experimental results show that the cost of electrical power consumption in kilowatt hour per month for operating the plant with closed-loop and open-loop speed control using VFD are GH¢23,049,289.72 and GH¢33,853,644.28, respectively. Simulations result also show that closed-loop control is advantageous for applications requiring high accuracy, efficiency, and responsiveness as it uses feedback to monitor and correct speed. Hence, per the experimental and simulation results, it is concluded that increasing the number of pumps with closed-loop for their operations will optimise the plant’s performance by enhancing its efficiency and also save energy.

This study has given the opportunity to assess and evaluate how VFDs can optimise the efficiency, save energy and reduce costs of operation at the Akim Oda water treatment plant. In motor life cycle, pump cost is 10% and energy consumption 90%, also according to green energy savings the amount of work or load on a motor is equal to amount of energy to power the work. VFD is a very cost-effective technology that can lead to better process control, so motor consume less power. The experimental results show that energy consumption per month for operating the plant with closed-loop and open-loop speed control with VFD are 41% and 59%, respectively. To evaluate the plant operation, MATLAB/Simulink was also used to simulate the system to observe the motor speed considering using closed-loop and open-loop speed control. The result shows that for high- precision with significant load variations, closed-loop control offers superior performance. Hence per the experimental and simulation results observation, it can be concluded that increasing the number of pumps for their operations optimise the plants performance by enhancing its efficiency and also save energy.

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