scope:

The aim of this guideline, which follows on from the definitions and examples provided in VDI 4608 Part 1, is to evaluate the efficiency of the combined generation or conversion of different target energies and to present different allocation methods, in conjunction with a recommendation for a scientifically based procedure.

In practice total costs have until now frequently been apportioned to the target products by the remainder value method. The present guideline proposes a differentiated procedure for this: It is recommended that the exergy loss method [1 to 3] be applied for allocating the primary energy, emissions and variable costs to the target energies. As regards allocation of fixed costs, it is recommended, in the event that a straightforward assignment is not possible, that apportionment be based on the ratio of plant costs at the time of investment in the reference plants and supplying heat and power.

In order to make the practical implementation of this guideline easier it includes a CD-ROM with a spreadsheet program which contains the following calculation sheets:

Fuel saving: Calculation of savings in primary energy for an efficiency assessment of a cogeneration plant for a defined supply task

Example 1 and Example 2: As an aid to understanding the examples in Annex B

Allocation: For calculations based on the allocation methods described here

Costs: For allocating variable and fixed costs and also total costs

Exergy: For calculating the specific exergies, enthalpies and entropies according to VDI 4670 for moist air and combustion gases in the application of the allocation methods