Graph‐theoretic reliability index for assessing the impact of capital and operating cost constraints in designing reliable energy hubs

Abstract Component failures in integrated heating and cooling networks impact reliable energy supply. This work studies reliability of heating and cooling systems constrained either by the annualized capital cost (ACC) or by the annualized total cost (ATC). A novel approach for assessing the supply reliability, representing energy networks as stochastic graph networks, is introduced, thereby enabling imposition of operational uncertainties and constraints as well as budgetary limitations as the graph networks' features. The reliability index is defined as the average percentage of the demands that are met. Single or multiple component failures may occur anytime; the reliability evaluation method is not restricted to one failure at a time. Examples of two different energy supply networks, maximizing the reliability under ACC or ATC constraints, are presented to illustrate the methodology. It is shown that, under ATC or ACC constraints, the 100% reliability and maximum consecutive loss of load hours (MCLOLH) equal to zero can be attained via a wide range of equipment sizes provided the thermal storage is sized correctly. Maps representing relative costs of heating, cooling, and storage, for the given system structure, help decision makers to determine equipment sizes if scaling up/down the system, while maintaining a high level of reliability.