The costs of space heating and domestic water heating account for the major portion of the energy costs of a private household. Nevertheless, many owners and tenants buying or renting a property do not know much about its energy consumption.

This undesirable situation has changed with the implementation of the EU Directive on the energy performance of buildings and the introduction of the energy performance certificate. Starting 2006, real estate owners will be obliged to present a certificate showing the energy values of their buildings. This disclosure obligations applies to both residential buildings and commercial properties that are constructed, sold or rented out.

The energy performance certificate shows several reference values that provide reliable and easily understandable information on the energy efficiency of the building. Under the EU Directive, national legislators can choose whether the energy performance is to be stated on the basis of the building ’s energy demand or its energy consumption. In the former case, each building is assessed according to a standardised procedure, so that the key values of the buildings can be compared. In the latter case, the building’s actual consumption is taken as the yardstick, e.g. on the basis of the heating cost statement. However, the energy consumption is dependent on the number of people living in the building and their consumption behaviour, so that this approach provides only limited information on the building’s actual energy quality. Apart from the overall energy efficiency, the energy performance certificate is to show additional key figures on the quality of the building’s insulation and its heating system.

The certificate may also indicate the CO2 emissions. According to the Directive, the certificate must also provide information on possible modernisation measures. Once issued, an energy performance certificate should be valid for a maximum of ten years.

The primary energy demand as a measure of energy performance

The annual primary energy demand Qp shows how many kilowatt hours of energy must be gained from a source of energy to heat a building and supply it with hot water. Qp is indicated per square metre and year.

Qh =annual thermal heat demand

This is the energy that the system must supply per year to heat the building. To calculate Qh, you add the heat losses in the building (ventilation and transmission losses) and deduct the heat gains (usable internal and solar gains).

Qw =demand for domestic water heating

Qw indicates the amount of energy needed per year to heat the domestic water.

ep =System efficiency ratio

Indicates the efficiency of the technology. The smaller ep, the greater the efficiency of the heating and domestic water heating system.

The Directive of the European Union, which had to be transposed into national law as of January 6, 2006, leaves the actual form of the energy performance certificate up to the individual member states. Germany plans to introduce an energy consumption label for buildings - similar to the energy efficiency classification of household appliances. The annual primary energy demand per square metre of useful space will serve as the yardstick. It is filled in an easily understandable colour scale, which allows the building to be compared with other properties at a single glance.

Under the German Energy Savings Directive (EnEV), the primary energy demand was introduced as the measure of a building’s energy performance in Germany already back in 2002.

Contrary to what was originally planned, the introduction of the energy performance certificate in Germany will be postponed by a few months. The federal government will probably permit both types of certificate during an initial period. The consumption-based certificate will temporarily be used for larger residential buildings.