Figure 1.7 The Load Curve of a District Heating System

from Eco cities (World bank,2010)

Traveling by Car, Bicycle, or Bus Figure 3.58 The Input-Output Framework of a Waste Management System

Peak load management: Managing the demand for services to minimize the requirements for peak capacity Energy, water, and transportation systems all tend to suff er from daily and seasonal peak loads that force utilities to use oversize systems to meet peak demand at a particular time or period. This may be signifi cantly ineffi cient from an economic and resource point of view. Peak loads also force utilities to supplement supply using backup or imported resources and services that are especially costly. Spatial systems likewise suff er because of the highly uneven demand for spaces that are dedicated to uses such as parking, roads, and restaurants.

The eff ort to reduce the need for greater overall system capacity through the management of daily and seasonal peak loads is known as peak load management. The object of peak load management is to even out the demands throughout the system and to distribute demand across time to avoid investment in new permanent capacity. In some cases, peak load management may also help avoid the high cost of topping up capacity if the primary system has reached maximum output.

By delaying or avoiding costly capital investments and costly backup strategies, peak load management may be extremely economical. It may also reduce resource consumption requirements and can make more optimal use of existing capacity. However, recognizing the best locations for intervention at each stage of the system requires a systems perspective.

For instance, in Europe, heat demand varies signifi cantly during the heating season. To deliver all district heating through a combined heat and power plant would require the utility to size a plant in accordance with the maximum heat load, which would mean greater investments. A strategy is therefore sometimes used whereby only the base load is supplied by the combined heat and power plant, while the peak load is supplied by a simple boiler plant (fi gure 1.7).

Peak load management is often applied in public transportation systems and highway systems to reduce overcrowding or congestion during rush hour. In Japan, most commuter railway systems adopt an off -peak-hour tariff (lower tariff ) to induce passengers to take trains during off -peak hours. The Tokyo Metropolitan Highway Authority also uses an off -peakhour tariff for highway tolls. The highway authority adjusts tariff levels across diff erent highway routes to divert traffi c from one route to another to reduce congestion.

Peak load management may also benefi t from a more collaborative approach because demand profi les are infl uenced by many factors that are sometimes diffi cult for cities to control unilaterally: land uses, time-of-day pricing structures, metering technology, control technology, business and school operating hours, daylight savings time, and the determination of the size of distribution and storage facilities at each level. Meanwhile, simple alterations to business and school operating hours may have a signifi cant impact on peak loads in transportation.