Annuity

This is an implementation of the calculation of economic efficiency using the annuity method defined in the German VDI 2067.

VDI 2067, Part 1

Economic efficiency of building installations

Fundamentals and economic calculation

September 2012 (ICS 91.140.01)

Copyright:

Verein Deutscher Ingenieure e.V.

VDI Standards Department

VDI-Platz 1, 40468 Duesseldorf, Germany

Reproduced with the permission of the Verein Deutscher Ingenieure e.V., for non-commercial use only.

Notes

The basic usage consists of two main steps:

Define an energy system sys with its components (called parts here)
Call sys.calc_annuities() to receive the annuities. Afterwards, you may also call sys.pprint_parts() and sys.pprint_annuities(), which are convenient pretty-print functions to view the results.

There are two main ways for adding parts to an energy system:

Manually input each part with its purchase price, service life and factors for effort for maintenance, etc. Please refer to the main method main_VDI_example() for this approach, which implements the example provided in the VDI 2067 Annex B and serves as a test
Select the parts from a database that contains all the properties. Here the only required inputs are name and size of a part (e.g. installed kW or kWh), all other information are derived from the database.

Deviations from the official calculations in VDI 2067:

If the service life of a part is T_N = 0, the number of replacements is set to n = 0. This applies to e.g. 'planning'. This approach leads to the correct results in the VDI 2067 example, but is not precisely documented.
VDI 2067 demands an observation period T > 0, for which the annuity factor is calculated. In addition to that, this implementation supports a 'simplified' calculation with T = 0, where the annuity factor for each part is calculated with its service life T_N.
This implementation includes the concept of funding, which is not part of VDI 2067. For each added part, the optional parameter fund can be given. The investment amout of the first year is reduced by that factor (fund=0 equals no funding, fund=1 equals 100% funding). Investment for all following replacements are not affected, they have to be paid in full. This does also not affect the operation-related costs. They are always calculated with the original investment amount A_0.