On operational planning problem deciding control/operational strategy of energy plant, the energy demand is handled as deterministic parameter. However, the energy demand varies momentarily in real operation. It is important to reveal the impact of forecast accuracy on control result when the operational planning problem is based on forecasted energy demand. This research in this year was done two tasks: one was energy system modelling with high resolution power meter for operational planning problem; the other task revealed the relationship between characteristics of energy system and energy demand. On the first task, I replaced the power meter with high time resolution in order to model the energy system with enough accuracy. The first task concluded that the operational model in 1~60 minutes time scale is able to adopt status transient model for building evaluation. On the second task, I analyzed the relationship between the characteristic of energy system and the forecast accuracy by numerical experiment. The second task suggested that the more efficient operational strategy under uncertainty of energy demand is that the energy system intends to supply more thermal energy than forecasted demand in order to avoid opportunity loss of energy production by cogeneration system.