REHVA nZEB technical definition and system boundaries for nearly zero energy buildings. REHVA Technical Report n. 4

This REHVA Task Force, in cooperation with CEN, prepared technical definitions and energy calculation principles for nearly zero energy buildings required in the implementation of the Energy performance of buildings directive recast. This 2013 revision replaces 2011 version. In order to prepare general technical definitions, it was needed to clarify how onsite and nearby renewable energy production is included in the assessment and how primary energy factors are to be used. For the uniform methodology, general system boundary definitions were established with the inclusion of on-site and nearby renewable energy sources. Proposed methodology refers to the use of standard energy calculation input data and energy calculation rules in order to compare objectively the energy performance of different buildings for compliance assessment purposes within the building types listed in the directive. These technical definitions and specifications were prepared in the level of detail to be suitable for the implementation in national building codes. The intention of the Task Force is to help the experts in the Member States to define the nearly zero energy buildings in a uniform way in national regulation. The directive requires nearly zero energy buildings, but since it does not give any harmonized requirements as well as details of energy performance calculation framework, it will be up to the Member States to define them. The directive formulates nearly zero energy building as a building that has a very high energy performance and requires the calculation of primary energy indicator. 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. Based on the directive’s formulation, a zero energy building was defined as a building using 0 kWh/(m² a) nonrenewable primary energy. Following the current understanding that nearly zero energy buildings are not cost efficient yet, led to the prepared definition based on technically achievable energy performance. Nearly zero energy building was defined as technically and reasonably achievable national energy use of > 0 kWh/(m² a) but no more than a national limit value of non-renewable primary energy achieved with a combination of best practice energy efficiency measures and renewable energy technologies which may or may not be cost optimal. This definition allows to take into account local conditions, but to use the uniform methodology in all Member States. With these definitions and energy calculation framework specifications, primary energy indicator and renewable energy ratio can be calculated as required by the directive. Calculation principles are explained with worked examples in order to assure transparent understanding of the definitions.