Professor Karsten Voss works at the school of architecture at the University of Wuppertal in Germany. His expertise is used in the International Energy Agency, where he and European colleagues develop international agreements about net zero energy building definitions
There is no international agreement about one net zero energy building definition. What results have you reached so far?
The energy codes of the different countries in Europe are still so different that it doesn’t make sense to set up a one and only definition. Instead we have agreed on a definition framework. The basic idea is that you have to agree on a kind of metric, for example, if you use primary energy or CO2 emissions to be the metric of the balance. You also have to agree on balance boundaries, for example, if you will include household appliances in the building energy balance or if you will include the embodied energy. The third point is the balance period. Will you do the balance over a year or over the life cycle of a building?
When do you anticipate that this definition work will be finished?
The major work started in 2009 and the definition work is now almost finished. The whole task goes until 2013. We have recently published a book on net zero energy buildings in German and it will come out in English in October. We will also publish a new article in the Energy and Buildings journal describing this framework. It comes into review next month, which probably will mean that the article will be published next year. This is a very important background for the different national legislative people to set up their definitions in their countries.
How many different definitions will there be?
There will basically be three to four types and it has to do with the metric, if you use emissions or primary energy and if you include or exclude household appliances and embodied energy. If you have a very energy efficient building, more than half of the emissions or the primary energy consumption comes from appliances.
If you compare Norway and Germany, what are the biggest differences that make it difficult to agree on a definition?
The biggest differences are that Norway will move forward with the wording net zero emission building and not net zero energy as Germany is doing and Norway is focusing more on a whole life cycle, including embodied energy, which is currently not the case in Germany.