Levels of modeling

While the number or variety of elements that a model encompasses does not change how a model is stored, it does help in planning both the initial model design and the information needed to complete a model analysis and get meaningful results. When considering the scope of a model, remember that it needs to be small enough for the relationships between properties to be well defined, but large enough to include some redundant data. Redundant data can be calculated from other data in the model.

At different levels of scale, or modeling scope, the consumers of the resulting information will change. For example, an engineer looking at equipment performance of a section of the facility may need more detailed information than a resource planning individual who tracks materials throughout a facility. The planner needs measurements in the model that are different from the measurement needs of the engineer. Elements that are common to both models use the same source elements; this aids in the construction of a variety of models using the same element library.

Three modeling levels, in order of increasing scope, are the following:

• Unit Model

  • This level of modeling typically includes the smallest details of information within a processing unit or area. This scope is useful for monitoring equipment performance and is used primarily by the engineers on that equipment. Auxiliary loops and heating systems that occur at this modeling level might not have influence outside of this area, and therefore would not be included at the next scale.

  • To perform a meaningful analysis on a unit level model, detailed data must be available on the materials and quantities within the unit. If there is only information available on the parameter of the unit (the inputs and the outputs), this is an indication that the data model is at its smallest granularity.

• Multi-Unit Model

  • When considering unit-to-unit type models, detail within the unit is typically summarized by the connections to and from that unit. Material added and sent to storage areas (tanks, stockpiles, etc.) would also be included.

  • At the multi-unit modeling level, measurements within the unit that do not affect the main inputs and output quantities are not included in the model.

• Boundary Model (Facility and Business Unit)

  • It is useful to create an analysis for the materials entering and leaving the "fence line" of the facility, further summarizing the unit-to-unit information to only the transactions to and from the process from material transfer points (shipping docks, weigh scales, tank feeds, pipelines). This level is also useful to analyze transactions between business units within a facility.