Life-Cycle Energy Analysis of a Water Distribution System

The paper presents a life-cycle energy analysis (LCEA) to quantify energy expenditures in the fabrication, use, and end-of-life stages of the pipes of a water distribution system. The methodology incorporates the capabilities of environmental input-output life-cycle analysis to quantify the energy required to fabricate pipes. The EPANET2 hydraulic model is applied in conjunction with a pipe-aging model to calculate the theoretical energy recovery in the use stage. An exponential pipe-break model is applied to quantify the energy required to repair pipe breaks during the use stage of a system. Simple formulations are developed to estimate the energy required to dispose of and recycle pipes once their service period has expired. The LCEA methodology is then applied to the New York City (NYC) water supply tunnels example to quantify energy expenditures in four planning scenarios with 10-, 20-, 50-, and 100-year pipe replacement frequencies. The results of the NYC example highlight the tension between the energy costs incurred in the fabrication and end-of-life stages of a system and those incurred in the use stage. A pipe-replacement period roughly equal to 50 years yielded the lowest overall energy expenditure in the three life stages. A sensitivity analysis was carried out to assess the influence of uncertain system parameters on energy expenditure estimates.