Starting from the final energy consumption data the Display® calculation instrument uses conversion factors to calculate the equivalent primary energy consumption.
For this conversion it applies the cumulative energy use factors. These factors describe the overall primary energy consumption which is linked with the creation or use of a product or a service, including all preproduction chains (extraction + transport + transformation) but without primary energy that is used as materials such as wood for the construction of a building or petrol for synthetic material. Furthermore, the energy utilised for the disposal (i.e. passive energy contained in the materials) is not taken into account. Since there is no widely used abbreviation for this factor in English so far we use the German abbreviation KEV in this users’ guide.
Contrary to the cumulative energy use factors the cumulative energy demand (CED) factors that are defined in the German guideline VDI 4600 include the amount of primary energy that is used as materials and that is reflected in the lower heating value of the product. They also take into account the energy input for the disposal.

The German Institute for Applied Ecology (Öko-Institut) has developed the life-cycle analysis program and database GEMIS. This program is capable of calculating the cumulative energy (KEV) use factors for a variety of different energy sources and processes.
On the basis of the processes linked to a service or a product the program also generates the greenhouse gas emissions related to the production or consumption of a product, given in kg of CO2 equivalents per kWh of energy. Since the respective conversion factor takes into account the sum of all greenhouse gas emissions on the chain of energy transformation it is cumulative, too. As already mentioned in chapter 2 the term CO2 emissions is used for means of simplification to express these greenhouse gas emissions.
The Display® calculation instrument uses conversion factors based on the GEMIS program, but produced by different sources:
The conversion factors for the energy sources gas, fuel, and coal result from a GEMIS version 4.14 calculations made by the Institute for Housing and Environment (IWU) Darmstadt, Germany. They are also used for the certificate of residential buildings developed by the German Energy Agency (dena).
The factors for wood, the production of hot water by a solar thermal collector, and for the production of photovoltaic electricity in the building are taken from the ProBas database which is run by the Umweltbundesamt. This data source is also used to provide most of the factors for the national electricity mixes.
The conversion factors that are used for district heat by default are also taken from a GEMIS version 4.14 calculation made by the IWU. Currently, the calculation instrument distinguishes only between one value for district heating networks with and one without cogeneration plants. It is intended to provide more precise conversion factors for the specified type of plant in the future. However, it is already possible to enter individual factors which are more adapted to the local situation by specifying the distribution of the energy sources consumed in the different heating production plants. This distribution is necessary in order to calculate the correct distribution of the different energy sources (Fossil, Nuclear, and Renewable).

There are different system boundaries for conversion factors that are used.
For gas, fuel oil, and coal the system boundary is the transfer point of the building, including the heat generator. The conversion factors for wood do not include transport and the heat generator.
Concerning all different utilisations of electricity, the conversion factors only include the generation of electricity. They do not take into account the transport of electricity or transformation processes in the building of the consumer.
For the use of a solar thermal collector, the conversion factor takes into account the energy input up to the transfer point of heat at the outlet of the device.
Further devices that are necessary to run the heating system are not included. The system boundaries are valid for energy conversion factors as well as for the CO2 emission factors.
In order to calculate the contribution of different energy sources (Fossil, Nuclear, Renewable) to the overall energy mix used in the building it is necessary to know the composition of the national energy mix for the production of electricity. For this purpose the Monthly Electricity Survey in its version from October 2003 that is published by the International Energy Agency (IEA) is used.