The main requirement of the current German Energy Saving Regulation (EnEV 2014) is the primary energy demand. The primary energy demand is calculated by an energy-source specific primary energy coefficient (PEF) out of the final energy demand or energy consumption.
The PEF is yet in many cases not an appropriate measure to determinate greenhouse-gas-emissions of a heating system or a final energy source. Therefore it has only a limited steering effect in terms of climate protection. Furthermore low non-renewable primary energy-factors (PEFne) are loosing the steering effect in relation to energy-efficient buildings and neglect other important aspects like resource availability of energy carrier.
The syndicate of the ITG, the ifeu and the Wuppertal Institute have created an overview-paper of possible further development for primary energy factors by taking into consideration of greenhouse-gas emissions. They show major deficits of the previous solution which are described and have worked out several suggestions for further development in consideration of CO2-equivalent emissions.
In conclusion, one suggestion for short-term implementation will be favoured, in which the previous indicator "primary energy" is supplemented with the indicator "climate protection". In the longer term the aim will be to take into account further sustainability indicators in the life cycle assessment of upstream chains of energy sources, heating systems and buildings. For this purpose more research is required.