The solution method employed by IDEA is iterative and uses the effective relational information. The algorithm proceeds stepwise through the system, balancing the imbalanced subjects and adjusting the related objects. The imbalanced objects become subjects in the following step. The first set of subjects are those affected by the boundary demands. The iteration terminates when there are no imbalanced subjects left to be adjusted.
The inventory model (IDEA) is currently capable of solving static systems only. It cannot be used for solving any balances other than simple substitutions. For example, the availability of waste paper cannot be taken into account, since all the profiles of alternative production technologies must be given as constants. Therefore, the framework of the inventory for each recycling scenario with collection rates and so on has been created separately with a worksheet program. In this section the main principles and procedures of the worksheet model are briefly discussed.
The principle of the worksheet model is based on the paper-fiber balance of Western Europe. The model computes the waste streams, available reuse fiber potentials and demands, and waste paper exchange between two regions of production and consumption. In this case the regions are Scandinavia, represented by Sweden and Finland, and Central Europe, represented by Germany, France, Italy, the Netherlands, the UK, and Austria. The method of computation makes use of the profiles for product characteristics, waste paper collection, and other factors given to it as parameters. The basic solution procedure, which is the same for both regions, begins at the paper supply. The steps involved are:
- Paper supply.
- Conversion (paper product manufacture).
- Consumption.
- Consumer disposal.
- Waste paper collection.
- Paper and board production.
- Waste paper raw material balance.
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