Nearly Zero-Energy Building’s (nZEB) Definitions and Assessment Boundaries

Abstract

How to define nearly zero-energy buildings? This is one major question for member states when implementing EPBD directive. The directive requires that energy performance of buildings, as well as the definition of nearly zero-energy buildings, should be expressed with a numerical indicator of primary energy in kWh/m² per year. Therefore, if a national energy frame (energy calculation methodology and minimum requirements) is not based on primary energy, first a new energy frame/methodology has to be developed and implemented in a building code in order to be able to implement the directive. This could be a major effort in countries where minimum energy performance requirements have been based on the requirements of building components or on energy need or on delivered energy. In this chapter, energy flows needed for the primary energy indicator calculation are described based on REHVA and CEN definitions, Kurnitski REHVA Report No 4, (2013), prEN 15603 (2013). A specific issue of nZEB buildings is accounting the positive effect of on-site and nearby renewable energy production, which needs to be included in the energy frame. Energy frame is described with system boundaries for each energy calculation step, starting from the energy need to the final system boundary of the delivered and exported energy, which allows us to calculate primary energy indicator and renewable energy contribution with national primary energy factors. Because of complicated definitions and system boundaries, calculation examples for all main cases are provided.