Near zero, zero and plus energy buildings: revised definitions

Here a survey of current definitions is the starting point to underline inconsistencies and critical issues, and to identify weak points. From these, distinguishing between energy and primary energy, with all its attributes, and between energy sources and energy carriers, a proposal of revised definitions of near zero, zero and plus energy buildings is formulated. This analysis is based on the use of the classic energy balance, but taking into consideration that a building is always a net energy consumer (it always produce entropy or destroy exergy). Special attention is then paid in clearly defining primary energy factors for energy carriers produced from renewable energy sources on site, nearby or far. Although the primary energy factors values have been fixed sometime by political reasons, a clear scientific definition is limiting them to a reasonable range these values, which at least do not violate the basic principles of thermodynamics. Finally, to clarify that a “plus” building cannot create energy but can just contribute to the local or regional electrical energy production by feeding the grid, a complementary energy index is then proposed beyond than required by the EPBD. This can overcome the questioning on the “negative” primary energy index that can be achieved by such building using some of current net ZEB definition. In this way is possible to spit the main function (and its quality) of a building from the secondary function (and quality) of being a distributed electric generator for the grid without losing any values and complying with the nearly Zero Energy Building definition of EPBD.