Net- and nearly-zero energy buildings: A review of teh definitions and case studies

Nowadays, we can come across different concepts related to Zero-Energy Buildings. Despite having common perspectives for reducing the environmental impacts, the methods and specific targets are different in different concepts. This paper reviews the terminology and calculation methods used in the two concepts of Net-Zero Energy Buildings (NZEB) and Nearly-Zero Energy Buildings (nZEB). It is concluded that despite sounding similar, different solutions will be reached by the two concepts due to different definitions, approaches, and set-targets. The NZEB aims at achieving the balance between the imported and exported energy in terms of a defined metric, while the nZEB will be reached when the best combinations of the available energy-related technologies assigned to a building are used and a minimum primary energy import is resulted. However, it does not necessarily mean that a nZEB will come very close to the zero balance. In the nZEB, a first step in the implementation is finding the cost-optimal solution, which relates the primary energy consumption with the life-cycle cost of the parameters of energy-conservations measures in the buildings envelope and the on-site energy generation. The paper presents the implementation of the two concepts in two case studies.