Box 3.9 The Eff ect of Distribution System Confi guration on Energy

BOX 3.9

The Effect of Distribution System Confi guration on Energy Consumption

The schematic represents a small town with hourly water demand of 450 cubic meters. The demand is split among nodes 2, 3, 4, and 5. The town is served through a fi xed speed pump from a reservoir at an elevation of 10 meters. For illustrative purposes, two scenarios have been considered. In scenario 1, link 1–5 does not exist. In scenario 2, link 1–5 has been constructed.

DISTRIBUTION SYSTEM DATA ANALYSIS RESULTS

Node Demand (m3/hr) Elevation (m) Pipe Diameter (mm) Length (m) Node Pressurea (m) Pressureb (m) 1 0 10 1–2 500 1,000 1 58.33 43.75 2 100 30 2–3 400 1,000 2 37.02 23.39 3 50 30 3–4 400 1,000 3 34.58 23.03 4 100 30 4–5 300 1,000 4 27.13 22.47 5 200 25 5–1 400 1,000 5 23.58 27.66

Note: m = meter; m3/hr = cubic meters per hour; mm = millimeter. a. Node pressure, scenario 1. b. Node pressure, scenario 2.

Results:

1. In scenario 2, the pump has been replaced by a smaller one, and the power demand has dropped to 71.5 kilowatts from 95.3 kilowatts (a 25 percent drop). 2. The annual energy savings is 209 megawatt hours, which may be equivalent to a savings of US$20,000 per year. 3. The capital investment to complete the loop and construct link 5–1 is less than US$100,000 and may be paid back in about fi ve years using the gain from energy savings. 4. Additional improvement may be achieved if a full optimization analysis is conducted to target the sizes of the pipes (diameters), while maintaining other hydraulic parameters such as fl ow velocities and node pressures within the recommended hydraulic design parameters.

Note: The hydraulic analysis has been conducted using EP-Net (enhanced prioritized Petri net) modeling software.

ponents of a water supply system. Storage capacity should equal one day of service. This capacity enhances water security in case of treatment plant stoppage, leads to smaller treatment and pumping facilities, reduces capital and operations costs, and enables optimal pump scheduling and intense treatment during periods of low electricity tariff s (usually nights and off -peak hours). Planners must balance potential savings with the capital costs of constructing storage tanks.

Storm water management

Storm water and rainwater harvesting and fl ood management: Storm water collection systems may be combined with sewage collection systems. Though this may reduce capital investment, treatment becomes more diffi cult if wastewater and storm water are reused. For this reason, these systems should normally be separate, complemented by effective and innovative water storage tools. For example, rainwater may be harvested