Optimization of the pipeline diameter of the water supply system

This study addresses the main pipeline of a water supply system. The paper reviews existing methods for determining the optimal pipeline diameter with the aim of minimizing both capital investment and operating costs. The aim of the study is to improve the method for calculating the optimal diameter by incorporating the dependence of electric motor power consumption on pump performance. The input data comprise the performance, energy and cost characteristics of centrifugal pumps; the physical and cost characteristics of high-pressure polyethylene (HPPE) pipes; and electricity tariffs. As in the conventional approach, the dependence of the cost and hydraulic losses of HPPE pipes on internal diameter is established. The proposed method introduces three substantive improvements. First, the performance and energy characteristics of pumps are approximated by second-order polynomials. Second, the pipeline inner diameter is determined such that the required flow rate is achieved at the operating point for each pump installed. Third, the hypothesis of constant efficiency is no longer required: power consumption is calculated directly from the corresponding dependence provided in the technical documentation. It is shown that efficiency changes significantly as the design flow rate or pipeline length increases. Under the conditions considered, efficiency decreases from 0.793 to 0.648 as the water flow rate rises from 60 to 80 m³/h. The influence of various factors on the optimal diameter of the main pipeline is examined. The optimal diameter decreases from 0.175 to 0.166 m as the pipeline length increases from 1000 to 9000 m. It increases with a longer project lifecycle and decreases with a higher interest rate.