According to the EU directive 2010/31/EU by 31 December 2020, all new buildings have to be nearly zero-energy buildings. But what exactly is a nearly-zero energy building?

The directive gives a purely qualitative definition: “A “nearly zero energy building” is a building that has a very high energy performance. The nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby.”

To find an answer for a qualitative definition for a nearly zero energy building the results of the USE Efficiency training course in the winter term 2010/11 have been analysed.
The students proposed measures for insulation and air tightness of the facades and high standard windows for all four buildings of the HCU campus. In a next step they calculated the primary energy demand after implementing a mechanical ventilation system with a heat recovery system. There is no need to cool the buildings. Furthermore an efficient heating system was proposed, also PV collectors on the roofs to produce electricity. In a last step the artificial lighting was changed to LED´s.

The primary energy demand of the refurbished buildings was now calculated with 80-90 kWh/m²a.

The students also made a design for the fifth building which has never been build, to complete the university campus (see figure 1). With the same measures they introduced for the existing buildings the primary energy demand for the new ones ranges between 65 and 75 kWh/m²a.

According to the German law it is compulsory to use renewable energy for a part of the thermal energy demand. Currently this has to be15%, but with a much lower energy demand of the buildings it could by increased up to 40% without increasing the absolute amount.

This ends up with a primary energy demand for a nearly zero energy building of 40 kWh/m²a. For the refurbishment of an existing building the benchmark would be 50 kWh/m² a