In such circumstances, different kinds of data (specified operating temperatures, batch duration, charge weights, number of starts and stops, etc.) may need to be recorded and fed into a mathematical model to arrive at a theoretical energy requirement given the pattern of production activity. This is another manifestation of an expected-consumption formula (ECF).
The model used as an ECF need not be complex, although indeed it may be so. The only requirement, from an M&T standpoint, is that the model yields a single number representing expected energy demand. Note that there will be a different model for each energy source feeding a monitored process: one for steam, one for electricity, and so on as the case may be.