Criticality

Criticality is the measure of risk associated with an asset. To determine which assets are critical, system staff need to know which assets are the most likely to failand the consequences if the failure occurs. Factors impacting the probability of failure (PoF) of an asset can be represented with a numerical rating scale (e.g. 1 to 5) ranging from a very low probability of failure to a very high probability of failure. The determination of consequences of failure (CoF) for a given asset involves the consideration of several tangible and intangible factors and can also be express numerically using a similar rating scale (e.g. 1 to 5). Multiplying PoFProbability of Failure and CoFConsequence of Failure ratings together provides the overall criticality score (risk score) for a given asset, with high scores indicating greater risk. Since energy use can impact an asset’s likelihood of failure and consequences of that failure, it should be considered in an assets PoFProbability of Failure and CoFConsequence of Failure ratings.

There are four modes by which an asset can fail: mortality, financial inefficiency, capacity, and level of service. Energy use can contribute to two modes of failure, financial inefficiency and level of service failure. If energy costs associated with an asset are too high, it can become financially inefficient to keep that asset in service. There may also be a potential for significant energy use reductions related to installing a more energy efficient asset. Similarly, if a system sets a Level of Service (LoS) goal to reduce its overall energy use, the system may replace an asset that uses a large amount of energy with a more energy-efficient asset to meet that LoSLevel of Service goal. Weighing the energy cost and savings of an asset will impact its PoFProbability of Failure score.

Consequences of an asset failure are a value judgement using the criteria of financial, environmental, and social impacts. These impacts can be valued differently by giving more weight to one type of consequence than another. When considering energy use, there may be benefits along with consequences when an asset fails. If a failed asset used a lot of energy, and there are feasible alternatives, the failed asset should be replaced with a more energy efficient asset. Alternatively, if a system has a level of service goal to reduce greenhouse gas emissions and the asset can be replaced by an asset that uses a “green” source of energy, replacement of the asset may be a good idea, even if this option is not the cheapest alternative. Replacing failed assets with green or more energy efficient assets will provide social and environmental benefits but doing so may also cost more. Converting from one source of energy to another (i.e. electricity to natural gas) may significantly impact the capital and operational costs and the cost change, whether positive or negative, should influence the CoFConsequence of Failure rating of an asset. When considering energy use, understanding how its environmental, social and financial impact may be an important part of the overall criticality evaluation.