Comprehensive parameters for the definition of nearly zero energy and cost optimal levels considering the life cycle energy and thermal comfort of school buildings

[Display omitted] •The share of Embodied Energy in total consumption of cost-optimal range is lower than 15%•The share of Embodied Energy in total consumption of nZEB range is higher than 80%•Various parameters are crucial to determine an applicable scenario.•In a hot-humid climate, the envelope improvement can lead to worsening comfort condition.•Being in the most cost-effective range does not necessarily make an action reasonable. There has been an increasing interest in studying energy efficiency in buildings in the recent years, as they account for a significant portion of energy consumption and greenhouse gas emissions worldwide. While most of the studies focus on the buildings' operational phase, a substantial part of buildings' energy consumption is disguised as embodied energy. It is impossible to have a zero energy building, as it is necessary to use materials to build the building, and those materials need to produce and transport energy. Life cycle analysis is the utmost efficient method to assess how a building affects the environment. Notably, the impact of buildings on the environment across their lifespans are determined by some factors, which comprise materials, design, construction, use and demolition. The study aims to present the implementation of a life cycle approach and occupant thermal comfort during the school building's energy efficiency design. The study's principal objective focuses on the energy use and environmental impact linked to various alternatives of building envelopes in different climates. Within this context, a reference building located in three different climatic regions of Turkey is investigated. Two ranges of efficiency comprise the focal points of the study. Cost-optimal and nearly zero energy levels are defined for each city. In the hot climate, the cost-optimal scenario cannot improve the comfort conditions, whereas the nZEB scenario improves slightly in such a context. In temperate and cold climates, both strategies can improve comfort conditions. The share of embodied energy and carbon in the nZEB level can reach higher than 80 percent, whereas it is lower than 15 percent in the cost-optimal level.