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Impact of Heat Supply Delays and Human Safety on the Reliability of Urban Energy Systems

The increasing use of energy conversion units like combined heat and power leads to a higher level of interplays between electricity, gas and heating systems in urban areas. Failure in one system may affect the operation of all other systems. However, differences in dynamic behaviors and service requirements are still not well studied, particularly in district heating systems with flow-dependent dynamic behaviors. This paper develops a quasi-steady state model for urban energy system to incorporate transport delays of pipelines and thermal inertia of buildings. Traditional reliability indices of heat services extracted from comfort temperature zone are extended to take into account nonlinear adverse impacts of low temperature on human safety. The results demonstrate that ignoring thermal dynamics may lead to overconservative reliability evaluation as short-term heat interruption has much less impacts than the outage. Meanwhile, the reliability of urbane energy system would be significantly reduced if indoor temperature remains below the safety value for a long period.